The individual: A 78-year-old man in the United Kingdom

The discovery: The man donated his body after death. While dissecting the cadaver, medical students made a "serendipitous discovery" in the pelvis, according to a report of the case.

Inside the skin of the scrotal sac and adjacent to a primary external penis were two smaller penile structures. Only the primary penis was externally visible, but all three penises included a bulbous structure called a glans and a chamber of spongy tissue that would fill with blood to create an erection, known as the corpus cavernosum.

What happened next: Doctors measured the three penises, finding that the external penis measured about 3 inches (7.7 centimeters) long and was 0.9 inches (2.4 cm) wide. The second penis measured 1.49 inches (3.8 cm) long and was 0.51 inches (1.3 cm) wide, while the third penis was 1.45 inches (3.7 cm) long with a width of 0.47 inches (1.2 cm).

Upon closer examination, doctors saw that there was only one urethra — the tube that transports urine from the bladder — which followed a "meandering course" through the secondary penis and then into the primary penis, terminating in the external penis' urethral orifice. There were no branches in the tunnel, and no additional urethral tubes were found in the third and smallest penis.

The diagnosis: During fetal development, a structure called the genital tubercle arises and eventually develops into external genitalia, forming either a clitoris or a penis. "In this case, there may have been triplication of the genital tubercle," resulting in three penises, according to the report. Possessing three penises is called triphallia. (The more common variant of this anomaly is diphallia, referring to two penises.)

The urethra originated in the secondary penis, but changed course and redirected into the primary penis when the secondary one failed to fully develop, the authors suggested.

The analysis: Instructors and students at the medical school did not know the man's identity, nor did they have access to his records or medical history. As a result, they were unsure if the man knew about his condition. Nevertheless, they expressed doubts in the report that his triphallia went entirely unnoticed.

Had the man required a urinary catheter insertion, the procedure would have been extremely challenging due to "the tortuous nature of the urethra" winding around and through his second penis, doctors explained in the report. They also noted signs of scarring in the man's groin from an inguinal hernia, in which abdominal tissue oozes through an opening in the abdominal wall called the inguinal canal.

Internal pressure or friction from the presence of two additional penises may have weakened the man's lower abdominal wall and contributed to the hernia, the authors theorized. Medical attention for the damage could have led other doctors to discover the supernumerary penises, they added.

What makes the case unique: The development of more than one penis is extremely rare, appearing in approximately 1 in 5 to 6 million live births, according to a 2010 review of published case reports; these cases are predominantly diphallia. The man's case was the first discovery of a triple penis in a cadaver, and the second known example of triphallia documented in scientific literature, in general.

In most cases, extra penises are associated with medical issues such as sexual dysfunction, fertility problems and urinary tract infections. When supernumerary penises cause physical discomfort or medical complications, a common solution is to surgically remove them. Or, if they are externally visible, the patient may choose to remove them for cosmetic reasons, according to the report.

Perhaps in this case, the authors speculated, the man knew about his triphallia but opted to forgo surgery "due to the apparent lack of symptoms" and the "benign nature" of his condition.

This article is for informational purposes only and is not meant to offer medical advice.

Can you guess the diagnosis in these strange medical cases? Find out with our diagnostic dilemma quiz!

New research offers a closer look at one of the least-studied organs in the human body: the clitoris, the structure responsible for female sexual pleasure.

Once described by a 16th-century anatomist as the "shameful member," the clitoris has historically been ignored in research in part due to taboo. Additionally, dissecting clitoral nerve tissue is challenging due to its position in relation to the surrounding pelvic organs.

In recent decades, MRI studies have characterized the overall structure of the clitoris. But only now have researchers captured clitoral nerves in three dimensions and at micron-scale resolution, thanks to an X-ray that uses an extremely bright light source called a synchrotron.

"Our research was able to show different parts of the clitoris," lead study author Dr. Ju Young Lee, a postdoctoral researcher at Amsterdam University Medical Centers, told Live Science in an email. She and her collaborators imaged two pelvises that had been donated postmortem to the university. The project was part of the Human Organ Atlas initiative, which aims to render whole organs in fine detail.

Their findings, which have not yet been peer-reviewed, were published March 20 on the preprint server bioRxiv.

Using CT images, the researchers traced the dorsal nerve of the clitoris (DNC) — the organ's main sensory nerve — from its origin point in a larger pelvic nerve structure. While prior studies reported that the DNC tapers off as it nears the clitoral glans, the external portion of the clitoris, the new imaging instead reveals that the DNC extends a robust array of branches into the glans. The DNC also splits off toward the mons pubis (the fatty tissue over the pubic joint) and the clitoral hood.

This work could be used to improve reconstructive procedures to restore the clitoris and clitoral function in patients who have experienced female genital mutilation, the study authors wrote. These procedures, which involve partial or total removal of the external female genitalia, are carried out mostly on young girls between infancy and age 15, can cause serious medical complications, and are considered a human rights violation, the World Health Organization states.

The new study may also help surgeons avoid damaging clitoral nerves during other operations on or near the vulva, the authors added.

Dodging nerve damage is key, since there is typically little overlap between surgeons trained to operate on genitals and those who treat peripheral nerves, said Dr. Blair Peters, an associate professor of surgery in the Oregon Health and Science University School of Medicine. Peters, who specializes in genital nerve procedures, and his colleagues published a tally of all 10,000 nerves in the human clitoris in 2022.

Although Peters was not involved with the new study, he told Live Science that the results align with his own observations.

"I have the privilege of actually seeing these things with my own eye," Peters said. Until now, "that hasn't been quantified in any meaningful way in the medical literature."

Peters added that medical recognition of the importance of genital nerves is on the rise, informed in part by insights from gender-affirming surgeries. However, more progress is needed.

"We have peripheral nerve treatments for everything else from head to toe, but the genital region is like a black box that's been unexplored," Peters said. "This anatomic work is super important to better treat a lot of medical conditions that for the most part have very limited options."

Lee said she hopes to expand her research to a larger sample size that covers a broader age range. Both of the imaged pelvises featured in the new work came from postmenopausal organ donors.

"I see this work as the beginning of a long journey for a new clitoris science," she said.

At first glance, teeth look a lot like bones: Both are hard, white and rich in calcium. So why aren't teeth considered part of the skeletal system? Even though teeth and bones share a few basic similarities, they're actually quite different.

The major resemblance between teeth and bones is what they're made of: hard tissue composed of minerals, such as calcium, phosphorus, fluoride and magnesium. On a molecular level, these minerals form a solid crystal structure, which is what makes both teeth and bones so much harder than everything else in the body.

"They're mineralized tissue," said Dr. Edmond Hewlett, a professor emeritus at the UCLA School of Dentistry. "But there, frankly, the similarity ends."

Functions of teeth and bones

One reason teeth aren't considered part of the skeletal system is that teeth serve an entirely different function than bones do, Hewlett said. The primary job of teeth is to break down food as it enters the digestive tract, though they're also important for producing speech. Due to their main job, your pearly whites are considered part of the digestive system.

Bones have different jobs. They provide structure and support to the body, creating attachment points for our muscular system. They also protect vital organs, housing key body parts such as the heart and lungs. And bones serve as production factories for both red and white blood cells, which carry oxygen around the body and play a key role in the immune system, respectively.

There is some small overlap in the functions of teeth and bones, though. The bones in the jaw do help to support the teeth and are important for chewing, for example.

"They work together but are separate," Hewlett said.

Structure of teeth and bones

Because bones and teeth do different jobs, they're also built differently. The outer structure of teeth is called enamel, a thin layer of mineralized tissue. Enamel is the hardest substance in the body — a property it gets from jam-packed crystals made from a compound of calcium and phosphate.

Underneath the enamel lies dentin, a type of mineralized tissue that's slightly softer than enamel but still hard. Dentin makes up the majority of a tooth's structure, and it contains tiny tubes that hold blood vessels and nerve endings. The core of the tooth is made of a jelly-like substance called pulp, which houses more blood vessels that provide nutrients to the tooth and to the nerves that control feeling in the tooth.

The structure of bones, on the other hand, looks completely different to that of teeth.

Bones are covered in a very thin, tough outer layer called the periosteum, which houses both blood vessels and nerves essential for growth and healing in the tissue. The next layer is composed of durable compact bone tissue. The inside of a bone contains cancellous tissue, a sponge-like substance with tiny holes that house bone marrow, where new blood cells are made.

Living vs. dead tissue

You might have noticed that, unlike teeth, bones are infused with nerves and blood vessels on both the inside and the outside. That's because bones are living tissue, whereas teeth are not — and that's one of the most important differences between the two.

Teeth form during fetal development and early childhood from specialized cells called ameloblasts and odontoblasts, which create layers of enamel and dentin that harden over time. Once that process is complete, the enamel-forming cells die off — meaning if a tooth is chipped or broken, that lost tissue won't grow back. While the pulp on the interior of the tooth is composed of living tissue, it can't help regenerate these outer layers of dentin or enamel.

Bones, by contrast, are dynamic structures that constantly remodel themselves. They contain a network of blood vessels, nerves and living cells called osteoblasts and osteoclasts that build new bone and break down old tissue, respectively. This constant turnover enables bones to heal after a fracture and to adapt to bodily changes, such as shifts in an individual's stress or activity levels. In fact, most of the adult skeleton is completely renewed about every 10 years.

"Bone is more of a living part of the body," Hewlett said. "But take care of your teeth — they won't grow back."

The human skeleton — our internal framework that includes bones and cartilage — evolved over millions of years. It comprises an axial skeleton, which consists of the skull and the spine, as well as an appendicular skeleton, which includes the shoulders, hips, arms and legs.

One of the main functions of the skeleton is to protect our squishy internal organs, but another important function is to help us move; bones act as levers with the assistance of muscles, tendons and ligaments.

Our jaws and teeth are also part of our skeleton, helping us eat and talk. From the top of our parietal bones to the bottom of our tiniest toe phalanges, our skeletons are a key part of our everyday lives.

How much do you know about your skeleton? Start our spine-tingling quiz below to find out.

Remember to log in to put your name on the leaderboard; hints are available if you click the yellow button!

No guts, no glory!

More science quizzes

—Conspiracy theory quiz: Test your knowledge of unfounded beliefs, from flat Earth to lizard people

—Brain quiz: Test your knowledge of the most complex organ in the body

—Heart quiz: What do you know about the body's hardest-working muscle?

Around 12,000 years ago, a man was shot by an arrow with an exotic stone tip in what is now Vietnam. He survived the initial injury but likely succumbed to infection, a new analysis of his remains suggests.

The man's well-preserved skeleton may be the earliest evidence of violence in Southeast Asia, the study authors claim, although some researchers say more evidence is needed to make that conclusion.

In a study published Wednesday (Aug. 27) in the journal Proceedings of the Royal Society B: Biological Sciences, the researchers detailed their analysis of the man's skeleton, dubbed TBH1. The man was about 35 years old when he died at least 12,000 years ago, during the late Pleistocene epoch (126,000 to 11,700 years ago).

The skeleton was originally excavated in 2018 from Thung Binh 1, a cave in the Tràng An Landscape Complex in north Vietnam. He had been buried in the fetal position, with his face resting on his hands.

Although the skull of TBH1 had been crushed, researchers were able to reconstruct his cranium and jaws. A first look suggested that, other than having a minor ankle injury, the man was in good health when he died.

But a more thorough analysis of the man's skeleton revealed an anatomical anomaly: an additional rib. Whereas most people have 24 ribs, between 0.2% and 1% of people have an extra one, called a supernumerary rib, the researchers wrote in the study. This man's extra rib was near his neck. Notably, TBH1's "bonus" rib was fractured, and it showed signs of infection; specifically, a gap in the bone where pus would have drained.

"TBH1 lived for several months after the injury occurred," the researchers wrote in the study. "Without effective treatment" of the fracture, though, "this is likely to have led to bacterial and other forms of infection," they wrote, leading to death from infection within weeks or months after his injury.

Related: Ancient jawbone dredged off Taiwan seafloor belongs to mysterious Denisovan, study finds

Near the infected extra rib, the researchers discovered a small, triangular quartz flake they described as a "micropoint." The point, which measured around 0.72 inches (18 millimeters) long, had evidence of notching. This suggests the point was used as a barb on a projectile, such as a dart or an arrow, study co-author Christopher Stimpson, a zooarchaeologist at the Natural History Museum in London, told Live Science in an email.

"The point is especially intriguing," study co-author Benjamin Utting, an archaeologist at the Smithsonian National Museum of Natural History, said in the statement. "It doesn't match any other stone tools from Thung Bunh 1 or nearby sites, raising questions about who made it and where it came from."

The combination of the micropoint near TBH1's neck, the man's infected rib, and the exotic nature of the quartz suggests the man may have been a victim of interpersonal violence, the researchers wrote. This would extend the evidence of violence between hunter-gatherer groups in east Asia back several millennia.

"This is an exciting new report from a time and place in which we have very few well-preserved skeletons to study," Michael Rivera, a bioarchaeologist at the University of Hong Kong who was not involved in the study, told Live Science in an email. "This quartz projectile could have been the culprit leading to an infected rib, but whether or not this was an act of violence or an accidental injury is difficult to assess, in my opinion."

TBH1 was likely cared for by his community, Rivera said, since the man survived his initial injury and was buried carefully in the cave.

Although TBH1 is a unique burial, Stimpson said, "the hill and its caves do seem to have had a longstanding role as a place of burial, as evidenced by the later archaeology" at the site.

Stone Age quiz: What do you know about the Paleolithic, Mesolithic and Neolithic?

An unsung appendage in the female body, which has long been considered useless, may actually be essential for ovary development and fertility, a new mouse study finds.

This structure, called the rete ovarii, was first discovered in humans over a century ago, but until now, it was considered a so-called vestigial structure — not crucial in adult female anatomy, but a leftover from fetal development. Vestigial anatomical structures, or "vestiges," are generally thought to have once had a crucial function that was later lost in the course of human evolution.

But according to a new study, published March 19 in the journal eLife, the rete ovarii (RO) may actually play an important role in ovarian function, and therefore, fertility. The work also showed that the structure has three distinct regions and may respond to hormonal signals.

"The female reproductive tract is often thought to consist of the vulva, vagina, cervix, uterus, oviduct, and ovaries," the researchers wrote in their paper. "We suggest that the RO be added to this list and investigated as an additional component of female reproductive function."

Although their study is based in mice, the researchers think it likely applies to people because the structure is also present in a number of other mammal species, including cows, cats, sheep, pigs, dogs and monkeys. Additionally, humans and mice share similar early sex-organ development pathways, so the scientists assume that the structure and its developmental cues might be similar in humans.

Related: 10 body parts that are useless in humans (or maybe not)

The RO is a horseshoe-shaped network of tubes nestled beneath the ovary, at the site where blood vessels and nerves enter the organ. However, despite the structure being highly conserved among mammals, when it was first found in humans in 1870, scientists deemed it to have no use.

"When this structure was first discovered in the late 1800s it was assumed that it had no purpose because scientists couldn't see its function within the body," Adam Taylor, a professor of anatomy at Lancaster University who was not involved with the recent study, told Live Science in an email.

At the time, "scientists also didn't have the same imaging, microscopic and molecular techniques available today," Taylor added. "These enable us to detect changes in blood flow, size changes of internal structures during life or ability to detect the proteins produced by the rete ovarii and compare these to similar ones produced elsewhere in the body where the function is known."

Now, in the new paper, researchers have applied modern methods to grant new insight into the RO. Some of their experiments used living mice, so that the researchers could study how the RO develops in the womb. Other tissues analyzed in the study were collected from euthanized animals after death.

The study found that the RO contains three distinct regions that mature during fetal development and then are maintained in adulthood. These regions include the intraovarian rete (IOR), located within the ovary itself; the extraovarian rete (EOR), made of convoluted tubules that join up into a bulb at one end; and the connecting rete (CR), a transitional zone between the IOR and EOR.

Using mass spectrometry — a technique used to identify and quantify molecules — the researchers discovered that, at birth, the EOR contains thousands of proteins within its tubes that its own cells appear to produce. One protein was insulin-like growth factor-binding protein 2 (IGFBP2), may be involved in ovary function. The protein may modulate the availability and activity of insulin-like growth factors (IGFs), which are structurally similar to insulin and important for the development of the follicles that carry immature eggs and hormones in the ovary.

In other experiments, the researchers watched fluorescent dye move through the EOR, revealing that fluid within the EOR is propelled toward the ovary. This further suggests that the RO has a role in ovarian function.

In another analysis, they found that the cells of the RO expressed, or switched on, genes that code for a variety of hormone receptors, including receptors for the sex hormones estrogen and progesterone. These hormones play important roles in female reproduction and health, helping to orchestrate the menstrual cycle, among other jobs.

"It appears that the rete ovarii may have a role in ovarian homeostasis - maintaining the ovaries and their environment," Taylor suggested. "Similarly they appear to be able to detect fluid movement in and around the ovaries and their microenvironment. Finally and most interestingly is the potential endocrine [hormonal] role that the rete ovarii may have."

The researchers behind the study suggest that the EOR may "act as an antenna" to receive signals from the rest of the body, both via hormones and nerves, and then send that information on to the ovary via the proteins it secretes and transports.

"There's still so much we can't even begin to comprehend about female anatomy," study lead author Dilara Anbarci, a developmental biologist at the University of Michigan, told Science News. "I hope this encourages more investigation in reevaluating what we don't already know about the ovary."

The researchers hope to further investigate the function and component structures of the rete ovarii, looking into how the EOR actually responds to hormones and whether the proteins it secretes change in response to changes in the body.

This research challenges the traditional view of the RO being considered redundant, proposing instead that it has a secret wealth of functions. Figuring out how the rete ovarii works could one day help scientists better understand and treat conditions of the female reproductive system.

"The endocrine system plays a key role in gynaecological health," Taylor said. "A greater understanding of any structures in this region has the potential to open up new therapeutic avenues and opportunities in treating various conditions."

Tomorrow (March 29), viewers in parts of the Northern Hemisphere, including in 13 states in the northeastern U.S., will get the opportunity to witness a partial solar eclipse.

This phenomenon occurs when the moon passes between the sun and Earth and partially blocks the sun, making it look like a bite has been taken out of our nearest star.

But staring directly at the sun without certified eclipse glasses can lead to an eye condition known as solar retinopathy, which can cause permanent vision loss.

So what is solar retinopathy and how can you protect yourself against it?

Related: How to watch tomorrow's sunrise 'devil horn' solar eclipse online for free

What is solar retinopathy?

Solar retinopathy occurs when intense light causes damage to the light-sensitive tissue in the retina.

The retina detects light and converts it into signals that the brain translates into the images that you see. Despite its name, solar retinopathy can be caused by any intense light source, including the sun, a laser pointer or the bright light from a welding torch. Solar retinopathy can occur within seconds of exposure to intense light in one, or more often, both eyes.

Anyone who stares at the sun, even on a regular day, can get solar retinopathy, Dr. Julie Rosenthal, a clinical assistant professor of ophthalmology and visual sciences at the University of Michigan, told Live Science. However, the eclipse is a time that those of us who don't weld or use lasers can easily get exposed to this kind of damage, she said.

People may be particularly vulnerable to solar retinopathy during a partial eclipse because the dark conditions caused by the sun being partly covered prevent the protective reflexes in the eye from properly kicking in, Live Science previously reported.

When it's light outside, for instance, people tend to squint their eyes while their pupils — which control how much light enters the eye — constrict to protect the retina, Dr. Sandra Montezuma, a professor of ophthalmology at the University of Minnesota, told Live Science. However, when it's dark, the pupils dilate, allowing more light to enter the eye and potentially damage the retina, she said.

Typically, people will not feel the damage happening as they stare at the sun as there are no pain receptors in the retina.

What are the symptoms of solar retinopathy?

A common symptom of solar retinopathy is blurred vision, often with a big blurred spot in the middle of your field of vision. Patients may also have distorted vision, for example seeing straight lines as being curved or perceiving objects as smaller than they actually are.

Other symptoms include headaches and changes in color vision when color-sending cells are damaged. Solar retinopathy can also cause a blind spot in a patients' line of sight. People may also complain that their eyes feel watery or sore.

The longer and more directly you look at the sun, as well as the more often you do it, the greater the damage. Symptoms of solar retinopathy may take hours or days to emerge after injury.

An eye doctor can image the retina to diagnose solar retinopathy, and to determine how much damage has been done to your retina.

Is solar retinopathy treatable?

There is no treatment for solar retinopathy, however, the condition will improve for many people during the first six months after damage occurs, Dr. Rosenthal said. Nevertheless, even if a patients' symptoms and vision problems get better over time, many may still have a permanent dark spot or see some wavy lines in their vision, she added.

In some cases, the retina may be so severely damaged that it does not repair itself. This can leave patients with permanent vision loss.

How can you prevent solar retinopathy?

The best way to avoid solar retinopathy is to not look directly at the sun, Dr. Montezuma said.

However, if people still want to view the partial solar eclipse on March 29, then they should ensure that they are either wearing solar eclipse glasses that comply with the ISO 12312-2 international standard, or using solar filters on skywatching equipment, she added. Solar filters are specialized filters that are added to equipment such as telescopes, binoculars or cameras that block sunlight.

If you don't have access to any of these things then another safe option is to just watch the partial eclipse online, Dr. Montezuma said.

"It's really a great time to be a part of science and to enjoy this cool phenomenon, but just make sure you're doing it safely," Dr. Rosenthal said.

This article is for informational purposes only and is not meant to offer medical advice.

Scientists have identified never-before-seen cells in the human eye that could potentially help reverse vision loss caused by common diseases, such as macular degeneration.

The researchers discovered the cells in the retina, a light-sensitive structure at the back of the eye that is vital for vision. The cells were found in donated samples of fetal tissue.

The scientists also identified the same cells in lab-grown models of the human retina — and when they tried transplanting those models into mice with a common eye disorder, it restored the rodents' vision.

"This research not only deepens our understanding of retinal biology but also holds immense potential for advancing therapeutic interventions in RD [retinal degeneration] diseases," the researchers wrote in a paper describing the findings, which was published March 26 in the journal Science Translational Medicine.

Related: Scientists restore monkey's vision with a patch made from human stem cells

The retina detects light and converts it into signals that the brain can then interpret to determine what we're seeing. Deterioration of the retina is a leading cause of blindness worldwide. It can be triggered by many things, including aging, diabetes and physical injury, and the degeneration can lead to common eye diseases, such as macular degeneration and retinitis pigmentosa.

Current treatments for these conditions focus mainly on reducing the rate at which retinal cells deteriorate, and protecting those that are still healthy. However, there are currently no effective therapies that promote repair of the retina, which would effectively reverse the deterioration.

A potential solution is to replace deteriorated cells with stem cells — cells that can mature to become any type of cell in the body under the right conditions. Yet, until now, scientists haven't found suitable stem cells in the human retina to achieve this, the authors of the new study wrote.

In the new research, the team analyzed the activity of cells in the fetal retinal samples in the lab. The scientists discovered two types of retinal stem cells with promising regenerative properties: human neural retinal stem-like cells (hNRSCs) and retinal pigment epithelium (RPE) stem-like cells.

The researchers found that both types of cells, which were located in the outer edge of the retina, could clone themselves. However, only hNRSCs could turn into other types of retinal cells under the right conditions.

In a separate experiment, the researchers grew miniature replicas of the human retina in petri dishes. These 3D tissue models, known as organoids, better mimic the unique complexities of human organs than traditional animal models do.

An analysis of the cells within these organoids revealed that they contained hNRSCs similar to those found in the fetal tissue samples. The team also identified specific molecular chains of events that turned the stem cells into other retinal cells and regulated the repair process.

When transplanted into the retina of mice with a disease similar to retinitis pigmentosa, the stem cells from the organoids turned into the retinal cells needed to detect and process light signals. These new retinal cells ultimately improved the vision of the mice, compared with rodents that didn't receive any transplanted cells. This effect was seen for the duration of the experiment, up to 24 weeks.

Taken together, these early findings suggest that hNRSCs could be used to develop new treatments for retinal eye disorders in humans. But more research will be needed to confirm the potential of these cells for restoring the vision of human beings.

Scientists have spotted unique subtypes of fat cells in the human body, and by unraveling their functions, they found that the cells may play a role in obesity.

The research, published Jan. 24 in the journal Nature Genetics, could theoretically open up avenues for new therapies to mitigate downstream effects of obesity, such as inflammation or insulin resistance, the scientists said.

"Finding these [fat] subtypes is something very surprising," study co-author Esti Yeger-Lotem,a professor of computational biology at Ben-Gurion University of the Negev, told Live Science. "This opens up all kinds of potential future work."

The findings suggest fat cells "are more diverse and complex than we previously thought," Daniel Berry, a professor of nutritional sciences at Cornell University who wasn't involved in the study, told Live Science in an email.

Related: Fat cells have a 'memory' of obesity, study finds

Over the past few decades, research has shown that fat tissue does a lot more than simply store excess energy in the body. For example, fat cells, also called adipocytes, and immune cells work in concert to communicate with the brain, muscles and liver. This, in turn, helps to regulate appetite, metabolism and body weight, and it's also involved in related diseases.

"If something is wrong there," within the fat tissue, "it affects other places in the body," Yeger-Lotem said.

Not all fat is created equal

Scientists have also long known that carrying excess fat is linked with a risk of health conditions. However, one of the many aspects of obesity that have left scientists puzzled is that not all fat is created equal.

Visceral fat — fat cells that reside in the abdomen close to the internal organs — is linked to a greater risk of various health problems than fat under the skin, known as subcutaneous fat. For example, excess visceral fat comes with a heightened risk of heart attack, stroke, diabetes, insulin resistance and liver disease. Studies also suggest visceral fat is more "proinflammatory" than subcutaneous fat, which could potentially contribute to the ill health linked to obesity.

To better understand what might be happening inside fat tissues, Yeger-Lotem and her colleagues charted a "cell atlas" of adipocytes as part of the Human Cell Atlas, a global project that aims to map all the cells in the human body.

The researchers built this map using single-nucleus RNA sequencing (snRNA seq), which measures which genes are active and to what degree by looking at RNA, a molecular cousin of DNA. RNA molecules act as blueprints for proteins, shuttling instructions from the DNA in the cell's nucleus out to its protein-construction sites. By measuring RNA in the nuclei of cells extracted from fat tissue, the team gathered clues as to what each cell does inside the tissue.

Yeger-Lotem and colleagues examined samples of subcutaneous and visceral fat collected from 15 people during elective abdominal surgeries. Most adipocytes were fairly "classical" — meaning storing excess energy was their main purpose. But a small proportion of the fat cells were "non-classical," as their RNA suggested they carried out functions not typically associated with fat cells.

Among these cells were "angiogenic adipocytes," which carried proteins usually used to promote blood vessel formation; "immune-related adipocytes," which make proteins related to immune cell functions; and "extracellular matrix adipocytes," which are related to scaffold proteins that help support cells' structures. These cell subtypes, found in both visceral and subcutaneous fat, were also confirmed under the microscope.

This "state-of-the-art application" of snRNA seq suggests these cells may play a role in "remodeling" fat tissues, Niklas Mejhert, a professor of endocrinology at the Karolinska Institute in Sweden who wasn't involved in the study, told Live Science in an email. Remodeling here refers to the way fat tissues change in response to weight fluctuations or metabolic changes. "Healthy" remodeling would help maintain metabolic balance, but if dysregulated, it could spur inflammation and other drivers of poor health in obesity, Mejhert said.

Related: In a 1st, scientists reversed type 1 diabetes by reprogramming a person's own fat cells

The study also spotted differences in the newly described cell types depending on which tissue they were taken from. Unconventional adipocytes from visceral fat seemed more likely to communicate with the immune system than those found in skin fat, Yeger-Lotem said. This link to immune cells suggests the cell subtypes might play a role in triggering visceral fat's proinflammatory nature, which could help explain why belly fat is worse for health.

The data also hinted that the fat-tissue donors with higher insulin resistance tended to have a higher concentration of these unconventional cells in visceral fat than did people with lower insulin resistance. However, Mejhert noted that the authors did not prove causation, so it's not clear whether the cells might drive the insulin resistance in any way. It's too early to know.

If these fat subtypes can be linked to human disease, understanding how they work could "help us fight inflammatory processes," Yeger-Lotem said. That could potentially help doctors predict the risk of insulin resistance in people with obesity, assuming all the dots connect, she added.

Berry cautioned that the study used a relatively small sample size and that, at this stage, it only suggests rather than definitively demonstrates that the fat cells have these unusual functions. Still, "these insights highlight the importance of understanding fat depots' unique behaviors to develop targeted treatments for obesity and related diseases," he said.

This article is for informational purposes only and is not meant to offer medical advice.

The little muscles that enable people to wiggle their ears unconsciously flex when we're trying to pick one sound out of a din of noise, a new study finds.

Think about how cats, dogs and certain monkeys twitch their ears in response to new sounds. This instinctive movement isn't just for show; it helps funnel sound toward the animals' eardrums, thereby sharpening their ability to pinpoint and process noise.

Recent research conducted at Saarland University in Germany revealed that humans also move their ears in response to sound — at least to some degree. When we strain to catch what someone is saying in a noisy room, for example, small muscles in our outer ears, called the superior auricular muscles, kick into action, likely in an attempt to sharpen our hearing ability. Because the muscle is small, though, it probably has little effect on our hearing ability.

Now, building on their previous research, the Saarland University scientists have conducted a new study, published Jan. 31 in the journal Frontiers in Neuroscience, to zoom in more closely on how the superior auricular muscle responds when people strain to hear. They think the research could have practical applications for improving hearing-aid technology in the future.

Related: 10 body parts that are useless in humans (or maybe not)

A remnant of our ancestors

Although the auricular muscles of modern humans are small and weak, in our distant ancestors, these muscles likely moved the ears back and forth, thus improving hearing by capturing sound more effectively. Some people can still wiggle their ears voluntarily, but nonetheless, these muscles are considered "vestigial" — evolutionary remnants with little practical use today.

That said, the researchers behind the new study wonder if the muscles could be useful for hearing-aid technology someday. One potential application is the integration of artificial intelligence that can sense and decode muscular movements.

"If the superior auricular muscles, the ones that perk the ears up, are activated, the hearing aid would know that the user is expending a lot of effort to hear and understand something," study co-author Steven Hackley, a researcher at the University of Missouri, told Live Science in an email. "The hearing aid would then boost the sound level for sounds coming from that direction," Hackley suggested.

To learn more about these small ear muscles, Hackley and colleagues recruited 20 participants with normal hearing and attached electrodes to their scalp to track electrical activity in their superior and posterior auricular muscles, which are found above and behind the ears respectively.

While seated in a soundproof room with their heads secured in a chin rest to prevent movement, the participants listened to an audiobook while a distracting podcast played at the same time. These sounds came from speakers positioned either in front of or behind the participants.

The participants completed 12 five-minute trials of this experiment, each at one of three difficulty levels: low, medium or high. At the easiest level, the audiobook stood out from the podcast with a decent volume and distinct sound, making it much easier to focus on. However, as the difficulty increased, the podcasts were made louder and took on a similar pitch to the audiobook. This shift made it more challenging, though not impossible, for participants to focus on the audiobook.

Based on the electrode recordings, the researchers noted that when sounds came from behind the participants, their posterior auricular muscles fired up more than when the sounds were played directly in front of them. This reflex may be a now-vestigial trait that once helped our ancestors detect sounds from outside their field of view, the researchers hypothesized.

By comparison, the activity of the superior auricular muscles wasn't affected by the direction of the sound. But as the listening challenge grew more difficult, these muscles became much more active. The study authors suggested that the activity of the superior auricular muscles correlates to listening effort, meaning how hard someone is consciously working to hear. However, other experts expressed caution in interpreting the results.

"I am not totally comfortable drawing that conclusion," Matthew Winn, a researcher at the University of Minnesota who was not involved in the study, told Live Science in an email. "The response might instead reflect arousal or noise frustration, which is a thing that "happens to you," as opposed to listening effort, which is a thing that you decide to bring to a situation," he suggested. "Arousal," in this context, refers to a state of heightened state of alertness, or responsiveness to sound.

Does this increased muscle activity help modern humans hear better? Probably not.

"The ear movements that we have been studying are probably too tiny to have any effect on hearing," Hackley said. "We call them "micro-movements" because they usually are less than a millimeter or two [less than one-tenth of an inch]."

Nonetheless, Hackley hopes these findings will translate into practical applications in the future, perhaps to augment hearing aids.

While some organs, like the brain, work continuously, other body tissues, like muscle and fat, can enter an inactive state. Muscles are typically inactive except during exercise, and a special type of fat — called brown fat — activates only in the cold to help warm us up.

When on standby, these two tissues burn very few calories and thus have a negligible impact on weight loss. But there's a notion that, if you build your muscles through exercise, those bigger muscles will burn more calories throughout the day. It follows that a person with a higher muscle-to-fat ratio would burn many more calories while at rest than someone with a lower ratio.

But does that extra bit of muscle really make a difference? And how does fat factor in?

How muscle burns calories

Calories are units of energy from food that power every bodily process, and the body stores an excess of them as fat. Most calories are broken down by continuously active organs, like the brain, heart, kidneys and liver, each of which burns 20 times as many calories as relaxed skeletal muscle.

Meanwhile, inactive muscle and brown fat use little energy: One pound (0.45 kilogram) of relaxed muscle burns 6 calories and the same amount of fat burns 2 calories in a day. But because muscle is one of the most abundant tissues in the body, it can burn a substantial number of calories when put to work.

Related: Why is it harder for some people to build muscle than others?

One study found that men who performed resistance training with hydraulic systems burned more than 12.6 calories per minute, and men who ran on a treadmill burned nearly 9.5 calories per minute — and that adds up quickly. By comparison, one pound of resting muscle burns only 0.004 calories per minute.

(Studies suggest that, when you adjust for body mass, there isn't a significant difference in calorie-burning during exercise between the sexes.)

"The best way to burn calories in any given [workout] session would absolutely be cardio," said Edward Merritt, a kinesiologist at Southwestern University in Texas. However, most people can't find the energy to do intense cardio several times a week, so he argued that resistance training — which grows muscles by placing them under tension — is a more sustainable approach.

However, Merritt cautioned against the misconception that muscles getting larger increases the tissue's calorie-burning metabolism, even at rest. According to myth, larger muscles burn more calories to maintain themselves, and each pound of muscle gained burns 50 calories per day while at rest.

"If you just lift weights and then sit on the couch, those muscles aren't necessarily burning that many more calories," said Gregory Steinberg, a metabolism researcher at McMaster University in Canada. However, "if you have more muscle, you will also be moving more weight around, and you'll burn more calories because you're doing more work."

Growing muscles through resistance training can help people burn more calories when they exercise, Merritt told Live Science. That's partly because big muscles tend to have more calorie-hungry fast-twitch fibers, specialized for lifting weights, rather than slow-twitch fibers built for endurance.

How fat burns calories

Most of our fat is "white fat," which is not helpful for burning calories; it mostly stores calories, insulates organs and releases hormones that regulate hunger. But humans also have "brown fat," which burns calories to regulate body temperature in the cold. This has led some to jump on the "ice bath" trend, which involves immersing yourself in frigid water in pursuit of various benefits, including calorie-burning.

But when you compare how efficiently brown fat and muscle burn calories, the results aren't impressive: Brown fat burns only 2 calories per day when inactive, and it would burn 20 additional calories during 90 minutes of cold exposure. The same number of calories can be burned with two minutes of muscle-activating exercise.

People probably don't have enough brown fat to leverage it for weight loss, Steinberg added. Most studies of brown fat's response to cold are conducted on rodents. Compared with people, he said, rodents have more brown fat to compensate for their small bodies that lose heat easily.

Ice baths may burn extra calories by inducing shivering, rather than activating brown fat, Steinberg suggested. Rather than taking ice baths, some people exercise at cold temperatures, but Merritt cautioned the practice. "If it gets too cold, you limit your blood flow to areas that might need it and it limits your ability to perform the exercise," he said.

One factor that's not fully understood is that people who do vigorous exercise tend to have more brown fat than people who exercise less. Future research could explore how exercise affects brown-fat abundance and how that impacts metabolism.

Editor's note: In this article, the colloquial term "calorie" refers to one kilocalorie (kcal), which is equivalent to 1,000 calories, in scientific terms.

This article is for informational purposes only and is not meant to offer medical advice.

Scientists say they've identified a new type of cartilage — one that was actually discovered in the 19th century, forgotten, rediscovered and then forgotten again.

Medical textbooks describe three types of cartilage: hyaline, elastic and fibrocartilage. Hyaline cartilage helps bones slide smoothly over each other at the joints; elastic cartilage is very flexible and found in the external ear, voice box, and tube between the ear and throat; and fibrocartilage is tough and absorbs impacts at the joints and in the spine. The cells within these tissues are surrounded by lots of collagen and elastic fibers, the proportions of which give each type of cartilage its distinct characteristics.

Now, however, scientists say there's a fourth type of cartilage that looks very different from the other kinds.

The tissue, which they call "lipocartilage," superficially looks a lot like adipose tissue — better known as fat. It contains bulbous, balloon-like cells filled with oils, and the cells are surrounded by a thin matrix of fibers, rather than a thick matrix common to other cartilage. The cells are also highly uniform and can pack close together like bricks. Together, the cells form a springy, squishy tissue that has a bit of give but still resists deformation and tearing; this tissue is found in structures like the external ear and nose.

Related: New part of the body found hiding in the lungs

Some experts were impressed with the new analysis of lipocartilage. For instance, Viviana Hermosilla Aguayo and Dr. Licia Selleri of the University of California, San Francisco wrote in a commentary that this "long-ignored cartilage type" may "warrant updates to histology and anatomy textbooks."

Others said that the researchers provided strong evidence of the tissue's existence but that they aren't sure lipocartilage merits its own classification.

"The authors provided evidence that this lipid-containing cartilage tissue exists in multiple mammals, including humans," Shouan Zhu, director of the Osteoarthritis Research Laboratory at Ohio University, who was not involved in the study, told Live Science in an email. But "what I am not sure [of] is if it should be considered as a separate new type of tissue or just a new feature of an existing tissue," namely, elastic cartilage.

What's old is new again

"This was a serendipitous discovery," study senior author Maksim Plikus, a professor in the Department of Developmental and Cell Biology at the University of California, Irvine, told Live Science in an email. The team was studying the skin of mouse ears when they stumbled upon the fat-stuffed cartilage cells, which Plikus compares to "Bubble Wrap."

But when they dug deeper, the team learned their discovery wasn't entirely novel. It turns out that other scientists had spotted this unique tissue before, Plikus noted.

In the 1850s, histologist Franz von Leydig wrote about his observations of rats' ear cartilage under the microscope. "At first sight it looks like adipose tissue," but it still has a distinct matrix, like cartilage, he noted. Leydig's observations would fall into obscurity for more than a century. Then, in the 1960s, scattered reports described similar fatty tissues in rodent ears. In 1976, a pair of scientists coined the term "lipochondrocyte" for the cells found in lipocartilage. But again, these discoveries were soon forgotten.

Now, with their study published Thursday (Jan. 9) in the journal Science, Plikus and colleagues offer a very close analysis of lipocartilage, revealing its stages of development, genetic traits and molecular characteristics. The study highlights how the tissue differs from its look-alike — fat — and how it's similar to other types of cartilage.

In mice, the team showed that the structures that hold the fat within lipocartilage are "superstable." Unlike fat cells, which get larger or smaller depending on food intake, lipocartilage cells don't shrink in times of starvation or swell in response to surplus. This stability partly stems from the tissue's lack of enzymes for breaking down fats, as well as from a lack of transporters that bring fats from food into the tissue, the team found.

"This characteristic may offer an evolutionary advantage for the ear pinna" — the outer ear — "by enhancing its ability to gather and focus acoustic waves," Zhu said. Sound waves ripple through fat very efficiently, so perhaps maintaining this high-fat cartilage in the external ear is useful for hearing, the authors also suggested.

Since the lipocartilage in the ear isn't going to swell or shrink depending on calorie intake, the acoustics it supports should also stay steady over time.

Where is lipocartilage found?

The study authors initially identified lipocartilage in the external ears, noses and throats of mice. "It is in the nasal cartilage at the very tip of the nose," Plikus said. "It forms the entire ear cartilage," as well as the vast majority of larynx, or voice box, he said.

"In all these places, a high degree of elasticity is required and unlike the body's other cartilages, such as joint cartilage, these structures are not weight-bearing," he added. For example, a structure in the throat called the epiglottis flexibly flaps back and forth during swallowing to stop food from getting into the respiratory tract.

After studying mice, the researchers also identified lipocartilage in human fetal tissues, namely from the ear, nose, epiglottis and thyroid cartilage, which sits above the thyroid gland. They also found that lipocartilage emerged in models of human cartilage that they grew from stem cells in the lab.

To see how prevalent lipocartilage is across the animal kingdom, the team examined museum specimens of dozens of species. They spotted the tissue in several mammals — such as the Cairo spiny mouse (Acomys cahirinus), squirrel glider (Petaurus norfolcensis) and Pallas's long-tongued bat (Glossophaga soricina) — but didn't find it in any nonmammals, such as frogs, birds or alligators.

The authors say questions remain about when lipocartilage first emerged and what evolutionary advantages it might offer to the animals it's found in. The team hopes to study the tissue's evolution, as well as investigate its ability to regenerate after injury and probe whether lipocartilage contains different subtypes of cells. They also want to better understand how the cells manage such high fat content, "which can be toxic for many other cell types," Plikus said.

"We believe these findings of a new cell type and new tissue type are fundamental and paradigm-shifting," he said of the work so far.

Editor's note: This article is part of a special package written for the 50th anniversary of the discovery of a 3.2 million-year-old A. afarensis fossil (AL 288-1), nicknamed "Lucy."

About 3.2 million years ago, our ancestor "Lucy" roamed what is now Ethiopia.

The discovery of her fossil skeleton 50 years ago transformed our understanding of human evolution. But it turns out her species, Australopithecus afarensis, wasn't alone.

In fact, as many as four other kinds of proto-humans roamed the continent during Lucy's time. But who were Lucy's neighbors, and did they ever interact with her kind?

For almost a million years, A. afarensis lived throughout East Africa, and paleoanthropologists have found numerous fossils of this species ranging from north central Ethiopia to northern Tanzania — a span of 1,460 miles (2,350 kilometers), or roughly the distance from Boston to Miami.

"It was a highly successful species that was comfortable in lots of different habitats," Donald Johanson, a paleoanthropologist at Arizona State University who, along with his graduate student Tom Gray, discovered Lucy's fossils in 1974, told Live Science.

For decades after Lucy's discovery, paleoanthropologists assumed A. afarensis was the only hominin that lived in this region during the middle Pliocene epoch (3 million to 4 million years ago). But the discovery of a fragmentary jawbone in the Bahr el Ghazal region of Chad in 1995 dramatically changed the picture of hominin diversity.

At 3.5 million years old, this fossil of a species that would be named Australopithecus bahrelghazali was the first indication that other hominins lived around Lucy's time, Yohannes Haile-Selassie, director of Arizona State University's Institute of Human Origins, and colleagues wrote in a study published in the journal PNAS in 2016.

Lucy's kind may not have interacted with these australopithecines, who were more than 1,500 miles (more than 2,400 km) away. But at the site of Woranso-Mille, just 30 miles (48 km) north of where Lucy was found at the site of Hadar in Ethiopia, Haile-Selassie and colleagues found A. afarensis fossils along with other, anatomically distinct fossils from the same time period.

These fossils belonged to a new australopithecine species: Australopithecus deyiremeda, which was dated to between 3.5 million and 3.3 million years ago. A. deyiremeda had markedly different teeth than Lucy's species, suggesting they had different diets, but paleoanthropologists do not currently agree on whether it is a different species from Lucy.

Woranso-Mille also yielded a partial foot dated to between 3.4 million and 3.3 million years ago, and its opposable big toe suggests this individual was better adapted for climbing than A. afarensis, a species that habitually walked on two legs. Although this individual was clearly not a member of A. afarensis, the "Burtele foot" has not yet been assigned to a species.

And at the Lomekwi site on the bank of Lake Turkana in Kenya, Meave Leakey, director of Plio-Pleistocene research at the Turkana Basin Institute in Kenya, and colleagues discovered another middle Pliocene hominin. The researchers named it Kenyanthropus platyops, Greek for "flat face". Dated to between 3.3 million and 3.2 million years ago, K. platyops overlapped in time with Lucy but lived over 620 miles (1,000 km) away.

K. platyops' brain was similar in size to that of A. afarensis, and the species lived in a grassy, lake-edge environment, much like Lucy did. While some researchers think K. platyops might be a Kenya-specific version of A. afarensis, others, including Haile-Selassie, think its upper teeth are different enough to call it a separate genus and species.

"A closer look at the currently available fossil evidence from Ethiopia, Kenya, and Chad indicates that Australopithecus afarensis was not the only hominin species during the middle Pliocene, and that there were other species clearly distinguishable from it by their locomotor adaptation and diet," Haile-Selassie and colleagues wrote.

This growing collection of fossils from different hominin species raises an important question that paleoanthropologists are trying to answer: Did these different species meet, or even mate with each other?

Almost all primates are social creatures, living in groups and cooperating to forage for food. And some nonhuman primates, such as tamarins, marmosets and howler monkeys, mate across species.

A. afarensis was as social as other primates, and Lucy may have lived in a group of 15 to 20 males and females. A preserved trail of footprints from three australopithecines walking together at the site of Laetoli in Tanzania is further evidence that Lucy and her kind were social creatures.

But there is currently little hard evidence that australopithecines mated across species, Rebecca Ackermann, a biological anthropologist at the University of Cape Town in South Africa, told Live Science in an email.

That said, "there is morphological evidence consistent with hybridisation in A. afarensis," particularly in the variation in their teeth," Ackermann noted. But these differences cannot be conclusively tied to interbreeding by current DNA techniques because australopithecine fossils are too old to harbor usable DNA.

Instead, we may be able to infer whether they ever interbred by looking at ancient proteins, which are coded for by DNA, she said. By looking at proteins in tooth enamel, Ackermann and colleagues clarified how individuals from the hominin species Paranthropus robustus, which lived in South Africa 2 million years ago, were related.

Despite the vast number of A. afarensis fossils discovered over the past half century, paleoanthropologists still have a lot of work ahead of them to fully understand the world Lucy inhabited.

"How these hominins were related to one another, how they interacted, how they filled niches on the landscape, and the degree of interbreeding that may have happened are open and important questions," Jeremy DeSilva, a biological anthropologist at Dartmouth College, told Live Science.

Lucy and her fellow australopithecines may have created and used tools more than 3 million years ago, a new study of hand muscles suggests. The finding provides further evidence that tool use started long before the Homo genus emerged.

"While we can't definitively say that these early humans crafted stone tools, our findings demonstrate that their hands were frequently used in ways that closely align with the actions necessary for human tool manipulation," study co-author Fotios Alexandros Karakostis, a paleoanthropologist at the University of Tübingen in Germany, told Live Science in an email.

In a study published in the November issue of the Journal of Human Evolution, researchers examined muscle attachment sites on the hand bones of three australopithecine species and compared them with ape and human hands to try to understand when our ancestors gained the dexterity that modern humans have. Since australopithecines represent the chronological mid-point in the evolution of humans from ancient apes, the researchers suspected that australopithecine hand bones may also have traits of both apes and humans.

The researchers focused on hand entheses, which are places where tendons attach muscles to bones. When muscles and joints are used frequently, these attachment sites adapt, resulting in a pattern of bony changes that suggest specific habitual activities.

"By studying these muscle attachment sites, we can reconstruct how muscles and ligaments were actively engaged throughout life, giving us a clearer picture of early hominin behavior," Karakostis said.

Related: Our mixed-up human family: 8 human relatives that went extinct (and 1 that didn't)

Muscle attachment sites on the hands of three australopithecine species revealed that they were all likely able to manipulate objects. But the comparatively recent hominin Australopithecus sediba (1.95 million to 1.78 million years ago) had a more humanlike hand than did the more ancient A. africanus (3.7 million to 3.4 million years ago) and A. afarensis (3.7 million to 3 million years ago), which both had a mosaic of humanlike and apelike traits.

Although apes can grasp and manipulate objects, their dexterity in these tasks is limited by their hand anatomy. Homo sapiens, meanwhile, have two key anatomical features that are essential to the ability to precisely grasp, grip and pinch objects, the researchers found.

The first dorsal interosseus muscle is located in the palm between the thumb and index finger and lets us precisely pinch things. "This unique functionality provided early hominins with the dexterity needed to manipulate objects — including tools — effectively, paving the way for both technological and cultural progress," study first author Jana Kunze, a paleoanthropologist at the University of Tübingen, said.

The pinky finger also plays a crucial role in humanlike grasping, the researchers noted. Early hominins like A. afarensis and A. sediba probably relied on pinky muscles for essential daily tasks such as handling tools and preparing food.

"More broadly speaking, the co-evolution of the thumb and pinky were decisive for hominin biocultural evolution, setting the stage for the advanced humanlike dexterity we see in humans today," Kunze said.

The question of how dexterous australopithecines' hands were is directly tied to the question of which species first made and used tools. When Homo habilis was discovered in the 1960s, scientists named it "handyman" because it was found with very old stone tools dating back 2.3 million years. For many years, researchers assumed australopithecines did not have the mental or physical capacity to make tools. But the 2015 discovery of 3.3 million-year-old tools at a site called Lomekwi in Kenya raised the controversial possibility that A. afarensis made them.

"Our study indicates that Australopithecus afarensis — the species Lucy belonged to — frequently performed humanlike grasping patterns, using their hands in ways that suggest regular, skilled manipulation of objects within the hand," Karakostis said. However, "these findings don't directly show that A. afarensis or A. sediba made or used stone tools in particular."

Tracy Kivell, director of Human Origins at the Max Planck Institute for Evolutionary Anthropology who was not involved in the study, told Live Science in an email that this muscle attachment research is novel and interesting, showing that each species interacted with its environment in different ways, including their manipulative abilities.

"It is likely that each of these australopiths were using tools and climbing," Kivell said, and the muscle attachment sites "provide exciting information about how these particular australopith individuals were using their hands during life."

Miniature livers will fly aboard the International Space Station in an upcoming study on whether microgravity can encourage the growth of healthy tissue with an ample blood supply.

It's an effort that could potentially lead to personalized, space-grown tissues and organs for use in transplant surgeries, scientists say. In two upcoming experiments, researchers plan to test how well the liver tissue grows in microgravity, as well as trial new technology designed to keep this tissue alive but super-cooled for its journey back to Earth.

"My ultimate goal for these tissues, if they are doing what we imagine and hope they are able to become with the help of microgravity, is to use these tissues for therapy," said Dr. Tammy Chang, a professor of surgery at the University of California, San Francisco. Tissue could be transplanted to treat a variety of liver-function diseases and disorders, Chang told Live Science.

Growing tissues in laboratory dishes on Earth can be challenging, in part because gravity pulls cells into contact with the bottom of a plate or dish. Gravity also puts cells under shear stress because, to keep the cells suspended as they grow, their dish needs to be agitated. In nature, after all, organs emerge in a developing embryo as it floats in amniotic fluid in the womb, or in the fluid cushion provided by an egg.

These everpresent challenges with gravity have led researchers to develop rotating bioreactors that simulate a low-gravity environment by spinning very quickly. This allows tissues and miniature organs, or "organoids" to grow in artificial conditions, but these rotating vessels also put stresses on tissues, especially as the cell clusters within them get larger.

Related: Scientists discover new type of cell in the liver

Chang and colleagues think organoids might grow better in a sustained, high-quality microgravity environment like that found on the International Space Station.

"These organoids that are typically the size of 200 microns in diameter, which is 0.2 millimeters [0.008 inches], will be able to further organize and interact with each other to develop larger tissues and, in particular, tissues that are vascularized," said Chang, who presented her research at the American College of Surgeons Clinical Congress 2024 in San Francisco on Tuesday (Oct. 22). Vascularized tissues are imbued with many blood vessels.

To grow their space-age liver organoids, Chang and her team use "induced pluripotent stem cells," which are adult cells reprogrammed to be stem cells that can give rise to different kinds of tissue. The researchers then coax these engineered stem cells to transform into liver cells and grow the cells in a special spherical bioreactor, called Tissue Orb. This globular reactor has a central conduit mimicking a blood vessel at its center. Nurturing organoids with this kind of circulatory system is key to growing larger pieces of tissue.

"Our concept is that these organoids in the main chamber can coalesce and interact with the central conduit and develop a more complex and larger vascularized tissue," Chang said.

The upcoming liver-tissue experiment will fly to the ISS in early 2025. The tissues will grow aboard the station for two weeks and then be fixed — set in a preservative solution — for analysis back on Earth. A second experiment, likely to take place later in 2025 or in early 2026, will test a supercooling system for bringing back live tissues Earthside.

These miniature livers aren't the first organoids grown aboard the ISS. Researchers are using space-grown organoids to investigate questions ranging from how the brain ages to how cancer develops and responds to drugs.

Flying an experiment aboard the space station is the culmination of many years of work, Chang said: "It is very exciting to have an experiment going aboard the ISS."

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Striking new psychedelic videos give a glimpse into what living organisms look like during their earliest moments — and it took scientists years to capture.

The videos are part of a new atlas of embryos called Zebrahub, which shows where cells are located and what they're doing at different stages of development. The atlas combines high-resolution timelapse videos of developing embryos with data revealing which genes are switched on at each developmental stage.

The atlas covers the embryos of zebrafish (Danio rerio), a type of minnow often used in biological research. The majority of the small fishes' genes have close analogs in humans, and the major components of cells are common across the vertebrate branch of the tree of life.

"At these early stages of life, all embryos are very similar," said Loïc Royer, one of the developers of Zebrahub, leader of the Organismal Architecture group and director of imaging AI at the Chan Zuckerberg Biohub San Francisco. "The shapes, the genes, the molecular machines that are responsible for doing that work of building an organism — it's all very similar."

Related: Early development is inherently 'chaotic,' new atlas of mammal embryos reveals

Royer is the senior author of a new paper describing Zebrahub, published Thursday (Oct. 24) in the journal Cell. He said that it's difficult to predict what kind of discoveries the new tool might enable, but studying the embryos of other lifeforms could address questions about how birth defects and other congenital disorders arise in humans. In addition, the new atlas may hold clues to why animals like zebrafish can regenerate their body parts following an injury, but we cannot, he suggested. And it could reveal key differences between youthful and aging tissues, which could help explain why we grow old.

At its core, Zebrahub focuses on one central question. "It's essentially the question of how we are built," Royer told Live Science. "If we don't know how we're built, how do we hope to 'repair' ourselves?"

Zebrahub is free to access and offers tools to help biologists view and use the trove of data. To collect the data in the first place, though, Royer and colleagues needed to develop new methods of studying zebrafish embryos.

Historically, studies have focused on either where cells are located within a developing embryo or which genes are active at a given moment. To track cells' locations, scientists take many snapshots of the embryos under a microscope. Zebrahub's developers created a new microscope that sweeps a thin sheet of light across the whole embryo, generating pictures as it goes. This technique avoids exposing the embryos to harsh lasers that could harm them.

The team used their microscope to capture timelapses of embryos from the time of fertilization through about 24 hours of growth. (Zebrafish hatch about three to four days after fertilization, so by Day 1, organs already start to form.) The researchers then analyzed these timelapses using a new software designed to track the movements of each individual cell in 3D space.

Historically, to track which genes in the embryo are switched on, researchers had to "melt" the embryos down, turning them into a "soup" that can then be analyzed by a machine, Royer explained. The problem is that you need 30 to 60 embryos, because turning them to soup inevitably damages some of their genetic material, limiting what's left to analyze.

Related: 'First complete models' of a human embryo made in the lab

The Zebrahub developers found ways of handling embryos very gently, preserving them well enough to analyze just one embryo at a time. They looked at more than 120,400 cells from 40 zebrafish embryos and larvae that ranged from 10 hours to 10 days old. They sequenced all the cells' RNA — a molecule that enables cells to make proteins from DNA's blueprints. The identity of a given cell can then be discerned from its gene activity.

At this level of resolution, the scientists spotted types of cells that tend to be missed through other methods, Royer said. For instance, they identified special stem cells — called neuro-mesodermal progenitors — and showed that they transformed into both nerve cells and muscle cells over time. It had been thought that the cells only gave rise to nerves.

Currently, the data in Zebrahub is based on two sets of embryos: one for the timelapses and one for the RNA. Nonetheless, these datasets can be compared to give scientists an idea of what an embryo looks like as certain genes are switched on. Looking forward, Royer and colleagues are working on collecting the same kinds of information from a single set of embryos, to better marry the data.

In the meantime, other groups of scientists are already using Zebrahub as a starting point to study human conditions. For example, one group combined Zebrahub with their own cell data to probe which proteins might drive cataracts to form in the eyes. They were able to see when various genes switch on and off as the lens of the eye first develops.

"We study fish because we cannot study human embryos, for obvious reasons," Royer said. "What we learn from the embryos, we learn about ourselves — so I study fish because I want to study myself."

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

A common food dye can turn the skin of living mice transparent, enabling researchers to peer inside the body without surgery.

This is the first time scientists have used the technique to visualize the tissues of living mice under the microscope. They used a food-safe dye, which can likely be found in snacks in your pantry, and several fundamental physics principles to render the mice see-through.

Biological tissue is chock full of stuff, from proteins to fats and liquids, and each substance differs in its ability to bend, or refract, light that hits it. This property is referred to as a material's refractive index.

If light particles hit a boundary between two materials with different refractive indices, those particles are forced to change direction, or scatter. While light can easily pass straight through transparent materials — like a glass of water — opaque materials get in the light's way, sending it bouncing in many directions. That light then bounces to your eyeballs when you look at the material, and thus, the brain interprets that scattered light as coming from an opaque object. That's why you normally can't see through someone's body.

Related: Scientists breed most human-like mice yet

But now, scientists have discovered a simple trick to change the skin's transparency: They took a concentrated food dye that is great at absorbing light, dissolved it in water and then applied the solution to the skin, which balanced out the refractive indices of substances within that tissue, making it temporarily translucent.

The researchers described this approach in a new study, published Thursday (Sept. 5) in the journal Science. They tested the technique on rodents using a U.S. Food and Drug Administration-certified color additive called tartrazine, also known as FD&C Yellow No. 5. This yellow-orange dye is often added to foods such as desserts and candy, as well as various drinks, drugs and cosmetics.

After initial experiments showed that tartrazine could turn slices of chicken breast transparent, the team turned to lab mice. They rubbed a tartrazine solution onto the rodents' scalps and then observed the animals under a microscope.

"It takes a few minutes for the transparency to appear," study lead author Zihao Ou, an assistant professor of physics at the University of Texas at Dallas, said in a statement. "It's similar to the way a facial cream or mask works: The time needed depends on how fast the molecules diffuse into the skin."

Once the solution set in, the researchers were able to see blood vessels streaming across the surface of the mice's skulls at a micrometer-level (0.001 millimeters) resolution. In a separate experiment, they applied the tartrazine solution to the mice's abdomens. Within minutes, they could clearly identify organs such as the liver, small intestine and bladder. They could even see muscles within the gut contracting, as well as subtle motions of the abdomen caused by breathing and the heart beating.

The transparency could be reversed by rinsing the mice's skin with water, ridding them of the food-dye solution. Any excess tartrazine that was absorbed into the body was excreted in the rodents' urine within 48 hours of application.

The treatment induced "minimal inflammation" in the short term, the researchers wrote in the study, but it didn't appear to have any long-term effects on the animals' health, as measured by changes in their body weight and blood-test results.

"This approach offers a new means of visualizing the structure and activity of deep tissues and organs in vivo [in the living body] in a safe, temporary, and noninvasive manner," Christopher Rowlands and Jon Gorecki at Imperial College London, wrote in a commentary of the new study. Neither Rowlands, a bioengineer, nor Gorecki, a physicist, was involved in the new work.

The new technique hasn't been tested in humans yet. Our skin is about four times thicker than that of mice, which would make it harder for tartrazine to be absorbed into its deepest layer. But if future studies show that the dye works in humans and it is safe, it could become a useful medical tool, the research team says.

"Looking forward, this technology could make veins more visible for the drawing of blood, make laser-based tattoo removal more straightforward, or assist in the early detection and treatment of cancers," study co-author Guosong Hong, an assistant professor of materials science and engineering at Stanford University, said in a statement.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Scars come in all shapes, sizes and colors and are the result of the skin's natural healing process after damage, whether it's caused by surgery, infection, injury or rapid body growth.

Scars serve an important role: They enable the body to replace lost or disfigured tissue. But what are scars made of? And why are they permanent?

To answer these questions, first it's necessary to clarify what a scar is.

The skin is made of three main layers. The outermost layer of skin, known as the epidermis, is the thinnest layer. It's composed of layers of flattened cells, called epithelial cells, which collectively act as armor, protecting the body from the outside world.

Related: Self-healing 'living skin' can make robots more humanlike — and it looks just as creepy as you'd expect

Underneath the epidermis is the dermis, the thickest layer of skin that contains nerves, blood vessels, hair follicles and sweat and oil glands. Within the dermis, there is also a large, fibrous network of proteins called collagen and elastin that, respectively, support the structure and elasticity of the skin. Finally, the hypodermis is the deepest layer of the skin. It contains fatty tissue for insulating the body, cushioning internal organs and shielding tissues from injury.

If you damage only the epidermis — such as in most cases of sunburn — this outer layer of skin will just peel off, leaving the deeper layers of skin intact. But if an injury penetrates deep into the dermis, the body then has to repair this damaged tissue. A scab forms to seal the wound, and then inflammation initiates healing. Then, the skin begins to remodel the tissue within that wound, and the haphazard way it does this is what causes a scar to form.

In normal skin, the dermis's network of collagen fibers is like a piece of fabric that is carefully woven in a nice, smooth pattern, Dr. Damon Cooney, an associate professor of plastic and reconstructive surgery at Johns Hopkins Medicine, told Live Science. If an injury tears this fabric, the body makes new collagen fibers to fill in any gaps.

However, instead of nicely weaving the new fibers back together across the wound, the body dumps them all together in a jumbled pile, Cooney said. This disorganized buildup of collagen makes up most scar tissue, making it look different from — and move less flexibly than — normal skin.

Scar tissue also differs from unscarred skin in that it doesn't contain any hair follicles or sweat glands. In people with lighter skin, a scar may first appear pink or red, but over time, this color will fade and the scar will become slightly lighter or darker than their normal skin color. The scars of people with darker skin will often look like dark spots.

Sometimes, the body continues to lay down collagen within scar tissue for longer than it normally would, causing what's known as a keloid or a hypertrophic scar to form. These are thick, raised scars that can be red, pink or purple, or just subtly darker than a person's normal skin tone. Keloid scars are larger than the original wound, while hypertrophic scars are the same size.

Adolescents and pregnant women are more likely to develop hypertrophic scars than other groups, possibly because of hormonal changes that boost inflammation in the body. Keloid scars are more common in people with darker skin tones, likely due to genetic risk factors.

Related: Why do wrinkles form?

Scars can fade over time as the jumbled collagen fibers within them begin to flatten and smooth out, Cooney said. This process can take around six to 18 months. How much a scar fades depends on its size, location and type. However, scars never fully disappear, because the jumbled tissue remains fundamentally different from the skin around it.

In theory, there could be a way to trigger scar-free healing in humans. Some animals, like salamanders, can completely regenerate wounded skin, leaving no scars behind. Humans can also do this, but only as fetuses, during the first two trimesters of pregnancy. Beyond that point, we lose the ability to regenerate wound tissue, and scientists don't really know why.

Animal studies have shown that skin transplanted from an adult to a fetus will still scar. This suggests adult skin cells are programmed in a way that causes them to scar, rather than regenerate, after injury. Differences in the number and location of stem cells within skin may also explain why only fetal wounds regenerate. However, this research is still in its infancy.

The "pie in the sky" goal would be to develop a therapy that allows the body to switch from scarring to regeneration, Cooney said.

In the meantime, some treatments can reduce the appearance of scars. For instance, laser therapy can change the color and height of a scar, while massaging a scar, especially with silicone gel sheets, can help smooth and flatten it, Cooney said.

Other treatment options include scar revision, whereby doctors surgically remove a scar and create a new one that is more uniform in appearance. Steroid injections can also reduce the size of hypertrophic and keloid scars. These injections help disband the collagen fibers in these scars and reduce the inflammation that can cause the tissue within it to swell.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

How did your heart form? What triggered your first heartbeat? To this day, the mechanisms of human heart development remain elusive.

Researchers know the heart is the first organ to fully function in the growing human embryo. It begins as a simple tube that starts to pump blood by the fourth week of gestation. By the ninth week, the heart is fully formed. The heart is critical to early development because it provides essential nutrients throughout the developing fetus.

But due to its early formation, the heart is exposed for a long duration to substances a pregnant person might come into contact with, such as medications or pollutants. This may be a main reason why congenital heart disease is the most common type of birth defect in people, occurring in over 1 in 100 births worldwide.

Traditionally, scientists have used animal and cell models to study heart development and disease. However, researchers haven't been able to produce a cure for congenital heart disease in part because these models are unable to capture the complexity of the human heart. Due to ethical limitations, using human embryos for these studies is out of the question.

To help researchers study heart development and complications in pregnancy, our team of biomedical engineers and cardiovascular scientists have spent the past several years trying to create the next best thing: mini human hearts in the lab.

Human heart organoids

Organoids are complex 3D cellular structures that replicate significant aspects of the structure and function of a specific organ in your body. While organoids are not completely synthetic, functioning organs (yet), they still possess immense power to mimic key aspects of physiology and disease in the lab.

We created our heart organoids using a type of cell called a pluripotent stem cell. Although using these cells in research used to be controversial because they were originally derived from human embryos, this is no longer a concern, as they can be produced from any adult. Pluripotent stem cells have the potential to become any type of cell in the body. This means that cells from nearly any part of your body — typically blood or skin cells — can be turned into your own stem cells to grow your own mini heart.

By manipulating the ability of pluripotent stem cells to become any type of cell in the body, we guided these cells to become heart cells. The cells were able to self-assemble, replicating the main stages of human heart development during pregnancy. Our heart organoids have blood vessels and all the cell types found in the human heart, such as cardiomyocytes and pacemaker cells, which give them an edge over 2D cellular models. Furthermore, the electrophysiology and bioenergetics of these heart organoids are very similar to human embryonic hearts in ways that animal models aren't.

Our heart organoids beat like a tiny baby's heart, all while smaller than a grain of rice.

Pregnancy and the fetal heart

One area we're exploring with our heart organoids is maternal and fetal cardiac health. Maternal factors such as diabetes, hypertension or even depression can increase the risk of heart disease in newborns. Studying conditions that increase the risk of congenital heart disease can prevent and reduce the incidence of cardiovascular diseases worldwide.

We can mimic these maternal environments and simulate how they influence fetal heart development with heart organoids. For example, we used heart organoids to show that diabetes, a very common condition, increases the risk of heart disease in embryos. Compared to heart organoids created in healthy conditions, mini hearts exposed to diabetic conditions developed heart abnormalities like those of human fetuses and newborns with diabetic cardiomyopathy.

Our study found that diabetes-related developmental abnormalities of the heart are likely caused by an imbalance of omega-3 fatty acids, the building blocks of cell membranes and signaling molecules. However, dietary supplementation of omega-3 fatty acids could partially restore this imbalance and prevent diabetes-induced congenital heart defects.

Drug safety during pregnancy

The drugs pregnant people take can have significant health effects on both the parent and the fetus. Medications approved for use during pregnancy are not always safe, since adequate testing is complicated. Ethical concerns limit working with biological material from people, so researchers are left with animal models that aren't able to replicate human physiology closely enough.

Testing medications on human heart organoids allows researchers to better explore and predict potential harmful effects during pregnancy. One example is ondansetron (Zofran), a drug commonly prescribed to prevent nausea and vomiting during pregnancy. Although it has been linked with an increased risk of congenital heart disease, whether it causes the disease hasn't been confirmed.

We showed that heart organoids exposed to ondansetron had disturbed development of ventricular cells and impaired function, similar to what's seen in newborns exposed to ondansetron. Our findings provide data that may help update clinical guidelines on the use of the drug.

Another example concerns the use of antidepressants during pregnancy, which is associated with an increased risk of congenital heart defects. Selective serotonin reuptake inhibitors, or SSRIs, the most prescribed antidepressants in pregnant people, work by increasing the availability of serotonin in the body. Serotonin is an important molecule in cardiac development. Maternal serotonin, along with antidepressants, readily pass to the embryo and alter serotonin levels in the developing heart.

In the future, we plan to expose heart organoids to antidepressants and study their effects on the incidence of congenital heart defects. The results of such research on human heart organoids may also inform recommendations for drug replacement or repurposing.

Heart organoids have the potential to help scientists more precisely study how the human heart forms and how it develops disease. In the realm of medical innovation, we believe human heart organoids grown from stem cells are the beating promise of a healthier future.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists have discovered a new type of cell in the liver that plays a critical role in repairing damage. 

These "leader cells" are responsible for dragging healthy tissue into wounds as they heal after injury, essentially filling the gap and allowing cellular regeneration to occur. 

This newfound knowledge could be used to create novel treatments for liver disease, researchers say. They described their findings in a paper published May 1 in the journal Nature. 

"Cutting-edge technologies have allowed us to study human liver regeneration in high definition for the first time, facilitating the identification of a cell type that is critical for liver repair," Dr. Neil Henderson, co-senior study author and a professor at the Centre for Inflammation Research at the University of Edinburgh in Scotland, said in a statement. "We hope that our findings will accelerate the discovery of much-needed new treatments for patients with liver disease."

Related: Dozens of unexplained cases of liver disease seen in UK children

The liver helps remove toxins from our blood, produces bile to remove waste products of digestion and metabolizes drugs. The liver also has the remarkable ability to repair itself after damage, for instance due to viral infections such as hepatitis, drug-induced injury and alcoholic liver disease. 

However, sometimes the liver is so damaged that it can't heal quickly enough, leading to acute liver failure, which affects more than 2,000 Americans a year. The condition can happen within 48 hours, potentially causing symptoms such as yellowing of the skin, excessive bleeding, brain swelling and multi-organ dysfunction. 

Depending on the cause, some cases of acute liver failure, for example those induced by poisoning, can be reversed with drugs. However, in severe cases, the only cure is an emergency liver transplant. There is, therefore, an urgent need for new therapies that enhance the liver's own natural ability to heal itself, say the authors of the new paper. 

To better characterize this healing process, Henderson and colleagues studied liver tissue from patients with acute liver failure who'd gone on to receive transplants. Although many liver cells from these patients could multiply, their livers still showed signs of significant damage. The team therefore wondered whether repairing the liver required more than simply making new cells to replace the damaged ones. 

So the team sequenced the genes of every liver cell, comparing those from patients with acute liver failure to ones from healthy individuals. This allowed them to generate an "atlas" of liver regeneration, showcasing which cells were active and when during the repair process, including the freshly-found leader cells.  

The team also viewed these cells in mice as they helped repair the liver after acetaminophen-induced injury. They noticed that during wound healing, leader cells emerge first, to rapidly close the wound, before cell proliferation helps further seal the gap. This suggests that the liver prioritizes wound closure before new tissue is made to prevent bacteria entering the organ from the gut and causing widespread infection, the authors wrote in the paper. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Scientists created realistic, miniature versions of a colon in the lab and gave them tumors, allowing the team to study colorectal cancer in exquisite new detail. 

These "minicolons"' are so-called organoids, which are 3D structures grown from stem cells such that they resemble full-size organs. In this case, the organoids were grown from mouse cells and driven to mature in a lab dish with the help of growth-inducing chemicals. 

Organoid development has become increasingly popular of late, namely because these miniature structures can more accurately mimic the unique intricacies of organs than traditional models made from cells can. This makes organoids great platforms for studying how diseases develop and progress, as well as for potentially identifying new drugs to treat those illnesses. 

So far, scientists have grown myriad tiny organs from both mouse and human cells. These range from minibrains to tiny replicas of testicles, and scientists are even conducting organoid research in space. 

In this latest installment, scientists have created colon organoids using mouse stem cells, which they say are much more complex than previous models. That's because the new minicolons contain a diverse mix of cells that are carefully arranged to reflect the true organization of the colon. 

Related: Lab-grown 'minibrains' help reveal why traumatic brain injury raises dementia risk

The team first developed this technology in 2020 as a way to model healthy intestines. But now, in a new study published Wednesday (April 24) in the journal Nature, they have demonstrated that it's possible to trigger colorectal cancer in these organoids by switching on cancer-driving genes in their tissue. 

In the experiments, colorectal tumors formed in the organoids in exactly the same way they do in mice, the researchers reported. The tumors could be grown in a lab dish for several weeks, allowing the team to watch how they change over time. 

A major advantage of this new model is that scientists can study colorectal cancer in much more detail, zooming in on specific groups of cells, Matthias Lütolf, co-senior study author and a professor of bioengineering at the Swiss Federal Institute of Technology in Lausanne, told Live Science. 

Because the new organoid is more complex than previous models, scientists can study not only which cells give rise to colorectal cancer but also how the individual cells within those tumors differ from each other — a phenomenon known as intratumor heterogeneity. Subtle differences in cells within a tumor can affect how the cancer responds to treatment, research suggests.

The new minicolons can also be used to study how conditions in the colon could potentially affect tumor formation. This includes the influence of a person's diet or the specific by-products of metabolism, or metabolites, that are made by resident microbes. Such experiments could reflect the true conditions in the body better than existing models that haven't considered these factors, Lütolf said.

Lütolf and colleagues also used the minicolons to identify molecules that may play an important role in why cancer develops in the first place. This suggests that these organoids could, in due course, become a valuable tool for identifying and testing new drugs to treat colorectal cancer. 

As a proof of concept, the team found that they could block the development of colorectal cancer in the minicolons by subduing an enzyme called glutathione peroxidase. This enzyme is normally used by tumors to help protect them from being attacked by the immune system. This finding hints that the gene that produces this enzyme could be a potential new drug target for the disease.   

Going forward, the team wants to grow these minicolons from cells that are derived from patients with colorectal cancer, so the researchers can develop an equivalent organoid for humans. There are key differences between mouse tumors and human tumors, so this step will make the work more relevant for cancer patients, Lütolf said. 

If these minicolons can be made using human cells, the organoids could become an "extremely powerful" tool for quickly testing different types of drugs against colorectal cancer, he added. They could also help answer questions about the role of other nearby cells, such as immune cells, in tumor development, he said. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

You take a sip of water but suddenly burst into uncontrollable coughing — your drink has "gone down the wrong pipe." It turns out that this familiar, protective response is instigated by rare, tiny cells in your airways, scientists discovered in a new study in mice. 

This finding could help pave the way to new methods for treating respiratory disorders, Ziai Zhu and Xin Sun of the University of California, San Diego, wrote in a commentary of the study. The researchers behind the work suggest it could be useful for treating chronic coughs, for instance, or preventing pneumonia.

When liquid enters the windpipe that leads to the lungs, rather than being swallowed down the esophagus to the stomach, the body automatically initiates safeguarding mechanisms. These include the cough reflex, which flings the liquid out of the windpipe, and the swallowing reflex, which gulps it down into the stomach. 

These reflexes help expel any inhaled fluid from the airways as soon as possible, to protect the delicate tissues in the lungs that allow us to breathe. If these protective mechanisms fail, bacteria within inhaled fluid can potentially trigger infection and inflammation in the lungs, known as pneumonia. Acid reflux triggers a similar set of reflexes when the contents of the stomach inadvertently travel back up the esophagus. 

Related: New cause of asthma lung damage revealed

These reflexes kick in thanks to nerves in the airways that relay danger signals to the brain. But these nerves don't do it alone — now, scientists have shown that the nerves get a helping hand from special cells in the lining, or epithelium, of the voice box and windpipe. These cells are known as neuroendocrine cells, and they're considered rare because they make up less than 0.5% of the airway epithelium. 

In the new mouse study, published Thursday (April 18) in the journal Science, the researchers revealed that these cells sense both water and acid in the upper airways. In response, they release a chemical called ATP that then activates nerves that shoot signals to the brain. 

These neuroendocrine cells were already known to be in the upper airways, because in rare cases, the cells can give rise to tumors in the voice box. However, the cells hadn't really been studied in terms of what they may be able to sense, Laura Seeholzer, co-senior study author and a postdoctoral scholar in physiology at the University of California, San Francisco, told Live Science. 

"Going into this study, I generally assumed that most of this [coughing] reflex was driven by sensory neurons," Seeholzer said. "So when I found that these rare epithelial cells were also detecting these stimuli, and that they were communicating with the nervous system, it kind of clicked that 'Oh, these cells could also be really important.'"

To take another look at the cells, Seeholzer and colleagues extracted them from the lungs, voice box and upper and lower airways of mice. They examined the cells in the lab to see which of their genes were active and what stimuli caused them to release chemical signals. 

They found that the neuroendocrine cells from the voice box and windpipe responded to water and acid, whereas the cells from the lungs responded to pressure, as has been shown in previous studies. When activated, these cells release ATP that, at least in mouse tissue in lab dishes, switches on sensory neurons that initiate swallowing and coughing reflexes. 

In separate experiments in living mice, the team found that activating these specific neuroendocrine cells in the voicebox and windpipe made the rodents swallow and cough. On the other hand, mice genetically modified to lack these cells were less likely to swallow water that ended up in their airways than mice who had their neuroendocrine cells intact. 

Since these cells seem key to triggering these protective reflexes, it's likely that their dysfunction could partly explain why some people struggle to swallow or often inhale water into their airways, Seeholzer said. Aging, for example, can make people more likely to accidentally breathe in food or water because the cough reflex can become dysfunctional. 

Recent research has shown that small molecules that block ATP from plugging into a specific receptor can reduce coughing in people with chronic cough. The activation of this receptor, called P2X, had previously been found to trigger swallowing reflexes in mice, backing the idea that it's key to both reflexes. 

P2X is also the receptor that neuroendocrine cells in the new study interact with. Therefore, the new findings could help uncover new treatments for chronic coughing conditions, Seeholzer said. 

But, given the new research was solely in mice, the team now plans to study these neuroendocrine cells in humans. In people, they hope to address the questions of whether these cells change as we age or as a result of chronic smoking, Seeholzer said. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website! 

Lampreys are the stuff of nightmares, complete with long, slimy bodies; circular mouths filled with teeth; and parasitic tendencies. But lampreys are also vertebrates, which means they have backbones and share a common ancestor with humans — and new research is revealing that we have more in common with these slippery bloodsuckers than scientists previously thought.

Lampreys belong to an ancient vertebrate lineage known as Agnatha, or jawless fish. Previous research suggests that lampreys and their relatives represent the most primitive group of vertebrates still in existence, having evolved an estimated 360 million years ago. These living fossils can give us a window into how some of our distant ancestors likely evolved.

For the last 150 years, scientists assumed that lampreys lacked a jaw because they were missing a structure known as the neural crest. This group of stem cells is unique to vertebrates, and in the womb or the egg, it develops into a wide array of structures. These structures include both jaws and the sympathetic nervous system, which controls our involuntary fight-or-flight response that kicks on in dangerous or stressful situations.

But a new study, published Wednesday (April 17) in the journal Nature, reveals that lampreys have sympathetic nerve cells after all — suggesting that the vertebrate flight-or-flight response is more ancient than scientists expected.

Related: Can you 'catch' stress from other people?

"Studies like this help teach us how we were built over evolutionary time," Jeramiah Smith, a computational biologist at the University of Kentucky who was not involved in the research, told Live Science.

The new study did not begin as a search for sympathetic nerve cells.

"One of the things I love about science is that you often make discoveries by accident," Marianne Bronner, a developmental biologist at Caltech and co-author of the study, told Live Science. Instead, the work started as a search for similar cells that were precursors to the more complex neural crest seen in jawed vertebrates. They thought they might find such cells in lampreys because they are the closest thing we have to ancient jawless vertebrates that first emerged around 500 million years ago.

But when the researchers started dissecting lamprey larvae, they noticed the immature fish had structures that looked a lot like neurons running in a chain down the length of their bodies. This string of nerve cells is characteristic of a sympathetic nervous system — a system lampreys weren't supposed to have.

When the scientists looked closer, they confirmed that these structures were indeed nerves using RNA sequencing; RNA is a cousin of DNA that helps cells make proteins, in addition to serving other functions. The team also found that the cells make a precursor enzyme for noradrenaline, a key chemical messenger that helps control the fight-or-flight response.

"Now it looks like the only thing that lampreys don't have is a jaw," Bronner said.

Lampreys were previously assumed to react to danger by relying solely on pheromones given off by other lampreys. (Ecologists still sometimes use these pheromones to control the critters' movements in the lab.) The discovery that these jawless fish have a fight-or-flight response places the evolutionary origin of this system about 50 million years earlier than scientists expected.

Bronner thinks that past researchers probably missed the sympathetic nerve cells in lampreys for a couple reasons. One is that the fish have a long developmental cycle; after a young lamprey hatches, it can spend years developing in a larval stage before maturing into an adult. The sympathetic neurons may be too small to notice until late in this developmental phase, and most prior research was done on newly hatched lampreys. The new work uncovered the cells in older larvae.

Another issue is that jawless fish are far less studied in evolutionary biology than "model organisms" like fruit flies and zebrafish, which serve as a model for biological systems also found in humans. Such species are great for lab work, especially as scientists know their genomes so well. But Bronner sees huge scientific benefits in studying creatures like lampreys, too.

"Sometimes you have to go outside of your comfort zone and work on these weird animals," Bronner said — nightmare fuel and all. So the next time your adrenaline spikes when you're watching a horror movie or you've heard a twig snap in the woods, consider thanking a lamprey.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Sitting in the grass of a Tennessee state park, Tracy Gregg felt the air grow cold as the late afternoon light she'd been bathing in suddenly faded. It was August 21, 2017, the date of a total solar eclipse that swept across much of the U.S., and she was directly in its path. Overhead, the moon was sliding into place over the sun, engulfing all below in shadow. In the brief darkness of totality, as lunar gloom consumed the land, Gregg tore her gaze momentarily from the sky to see the verdant meadow around her surprisingly transformed, now saturated in striking hues of violet and lavender.

Gregg, like most other people privileged to witness this rare celestial event, had experienced what is called the Purkinje effect, or a natural shift in color perception caused by fluctuating light levels. In bright light, colors such as red and orange are rich and vibrant to the human eye, compared with blue and green. But in dim light, red and orange become dark and muted, while purple, blue and green brighten. Sunlight's rapid, dramatic dimming during a total solar eclipse can heighten this phenomenon, making such events all the more surreal.

On April 8 the moon will once again pass fleetingly in front of the sun as seen from a continent-spanning swath of North America, giving those lucky enough to be in the path of totality an opportunity to watch the Purkinje effect in action. "I just remember the overall color being this deep purple that lasted for only about seven or eight minutes," says Gregg, a planetary scientist and self-proclaimed eclipse enthusiast, who chairs the department of geology at the University at Buffalo. "I admit being a little nervous to take off my eclipse glasses, but when I did, I saw that the whole sky was just lavender.... It was the whole sensory package."

Our perception of this color transformation arises from the specific anatomy of our eyes. Working within the retina — a light-reactive layer of tissue at the back of the human eye — are two types of cells called cones and rods. Cone cells provide photopic vision, or the ability to see clearly and perceive colors in well-lit spaces, whereas rod cells give scotopic vision, or the ability to see in dim light but with much less color. Murky conditions such as twilight or a solar eclipse's totality prompt our eyes to enter mesopic vision, in which the retina's rods and cones work together.

But simultaneously active rods and cones don't give humans super clear and colorful vision in medium-lit conditions as one might hope, says Jay Neitz, a professor of ophthalmology at the University of Washington. Instead the result is a sort of hybrid vision in which the eyes can perceive only some colors. "Rods and cones don't have separate signal pathways to the brain," Neitz says. "So information from both of them converges on the very same set of fibers that are linked to our brains..., and we end up with competing signals in the mesopic period."

Human retinas have three types of color-sensing cones: red, green and blue. Combinations of these cones allow us to see all the colors of the rainbow in broad daylight. But in the mesopic period, signals from red cones (which sense longer, ruddier wavelengths of light) are lost, whereas those for the shorter wavelengths sensed by green and blue cones persist. This is why greens and blues are so noticeably vibrant during twilight and a solar eclipse, Neitz says. "At the very peak of our rods' sensitivity is a wavelength that looks like cyan or the color of the ocean," he adds. "That's the color that really penetrates and is probably most beautiful during [a solar eclipse]."

For other animals, an eclipse-induced Purkinje effect may be even more intense, says Freya Mowat, an assistant professor of ophthalmology at the University of Wisconsin–Madison School of Veterinary Medicine. Birds have a fourth cone that lets them see ultraviolet light. It's difficult to say exactly how the sudden light change during a solar eclipse would affect avian vision, Mowat, says but it's possible that the shades of purple would be extra vivid and disorienting.

Dogs, however, probably miss out on any mind-blowing visual shifts because their retinas contain only two types of cones: blue and yellow. What dogs likely see instead, Mowat says, is a muddy and pale reddish brown, and they may not care much for the solar spectacle.

Humans, though, should have some fun and toy with colors during April's eclipse, Neitz says. It's a rare occasion in which the sun's light dims and brightens so quickly that the Purkinje effect becomes clear. "Every day it goes from being bright outside to dark at night over a period of a couple hours," he says. "But we're usually busy when that happens, and it's so gradual that our rods have already begun to adjust, so we hardly even notice there's something kind of amazing going on. During a [total solar eclipse], you actually get to witness this fantastic transition that goes from photopic to mesopic to scotopic and back again."

Solar Eyeglasses, a company that sells eye-protecting eclipse shades, recommends that spectators gathering in groups wear reds and greens to elicit the greatest visual contrast. Neitz suggests watchers include a bag of colorful Skittles candy in their eclipse starter pack to see how hard it is to guess which flavors they're about to eat as the sun fades.

Gregg will view this year's total solar eclipse from her hometown of Buffalo, N.Y. — a prime location in the path of totality. Her essential eclipse item is an old-fashioned camera. "Maybe it sounds mundane, but I'm going to pull out my old camera with settings that can be manually adjusted," she says. "Our smartphone cameras adapt to every setting. But I don't want a modified photo. I want a representative photo that captures light and colors and all."

This article was first published at Scientific American. © ScientificAmerican.com. All rights reserved. Follow on TikTok and Instagram, X and Facebook.

Out in space right now, scientists are growing tiny, three-dimensional models of human organs. What may feel like a scene pulled from the beginning of a sci-fi film is actually a relatively new application of a type of research that's already breaking boundaries of discovery back on Earth. 

From tiny, beating hearts to "mini-brains," so-called organoids are usually grown from human stem cells that, with the help of a cocktail of growth chemicals, can be pushed to self-organize into 3D structures that resemble tissues in the human body. Unlike traditional animal models, such as mice or monkeys, organoids allow scientists to more accurately recreate the unique intricacies of human organs. Therefore, these tiny organs could help accelerate drug development by helping to reveal which compounds will really work in humans and which ones won't.  

Organoid research can be described as out of this world — in some cases, literally so.

Since 2019, tiny models of organs — including the brain, heart and breast — have been grown on the International Space Station (ISS). But this research raises a question: Why are scientists crafting miniature organs in space?

Related: Tiny lab-grown testicles look remarkably like the real thing under the microscope

Aging organoids in microgravity

One reason is that the harsh environment of space could help scientists study aging and related disorders that affect humans back on Earth.  

Alysson Muotri, a professor of pediatrics at the University of California, San Diego (UCSD), has been sending human stem cells to the ISS for years, with the goal of growing brain organoids that model various diseases. Disorders such as Alzheimer's disease can take decades to develop in a person, but studies suggest that the low gravity in space can accelerate aging in cells. So, by studying brain organoids in microgravity, scientists could pinpoint how age-related changes happen and help devise treatments to prevent them.  

Many approaches to modeling the aging brain have involved stressing neurons in lab dishes, by adding certain chemicals, for example. However, these experiments don't capture what really happens as the body ages, Muotri told Live Science. "You don't receive like a cascade of molecules in your brain that makes you age overnight," he said.

The team's organoid research was inspired by the NASA twins study, during which astronaut Scott Kelly went to space for a year while his identical twin brother, Mark, stayed on Earth. When Scott came back, he showed signs of enhanced cognitive decline compared with his brother; he found it harder to learn and memorize things, for instance.

It's unknown why these effects were seen, Muotri said. One theory is that it could be because microgravity reduces the activity of an enzyme called telomerase, which helps reverse the natural process whereby sections of DNA at the end of our chromosomes shorten as we age, he said. These aglets at the ends of our DNA are called telomeres, and because shrinking telomeres are linked to aging, some scientists think lengthening telomeres could fight aging and extend the human life span. 

In an upcoming paper, Muotri's team will fully describe how the brain organoids are behaving on the ISS — but from what they can tell so far, the organoids that have already returned to Earth are showing signs of accelerated aging, Muotri said. The brain organoids show features of neurological diseases, such as degeneration and cellular stress, commonly seen in several conditions. This has allowed the researchers to test new drug candidates for the diseases, with promising early findings. 

"The first paper will report the first drug that was discovered in space for a brain disease," Muotri said. However, the exact publication date has yet to be confirmed.

Related: In a 1st, 'minibrains' grown from fetal brain tissue

Tiny tumors in space

The NASA twin study also inspired another UCSD research team to grow organoids in space — but rather than minibrains, they're tiny tumors. The team is led by Dr. Catriona Jamieson, a professor of medicine. 

After returning to Earth, Scott Kelly was found to have signs of shortened telomeres, DNA damage and signaling molecules in his blood that are known to activate certain genes that allow cancer to grow and spread. This suggests that the stressful conditions in space could somehow stimulate cancer growth and could therefore be a good model for studying how the disease develops, Jamieson told Live Science. 

The team started by sending blood stem cells to space, and after just one month, the cells showed signs of cancer-related genetic mutations being switched on. These changes were tied to abnormal growth and division in the cells. 

The researchers then sent a bunch of tumor organoid models of leukemia, colon cancer and breast cancer into space with the private Axiom Mission 1. They found that the models also grew "dramatically" while on board. The cells within the organoids also switched on a gene called ADAR1, which codes for an enzyme thought to allow cancer to multiply. In a separate experiment, the team were able to show that two drugs which inhibit ADAR1 — fedratinib and rebecsinib — could slow the growth of the miniature tumors. 

Now, as part of their latest launch to the ISS in January 2024, the team is testing the cancer-busting potential of these drugs in more breast cancer organoids.  

"We're very pleased to work with NASA on trying to accelerate the development of the world's first ADAR inhibitors, a small molecule that would be given intravenously," Jamieson said. 

Related: Scientists develop 'crying' model of human eye tissue

The future of organoids in space

This research is as much about protecting people on Earth as it is for helping astronauts in space. One day, for instance, Jamieson envisions that people taking part in commercial space flights could be given a pill before they go, to protect the stem cells in their blood from turning cancerous. Back Earthside, using their discoveries in space, the researchers are planning to start a clinical trial of rebecsinib later this year to target myelofibrosis, a blood cancer that scars the bone marrow. 

Other researchers have taken advantage of the potential dual benefits of this kind of extraterrestrial research. They include Catherine Yeung, an associate professor in the School of Pharmacy at the University of Washington, whose team has been studying how the accelerated aging environment in space affects the kidneys. 

Rather than organoids, Yeung's team is using a different model of human tissue known as an "organ-on-a-chip" device. This technology mimics human tissues on credit-card-sized devices and are seen as complementary to organoids.

Related: Scientists invent 1st 'vagina-on-a-chip' 

"If we can learn things from space that can help us treat conditions on Earth, I think that's the overarching goal — I don't know that we need to choose one or the other," Yeung told Live Science. 

Growing organoids on the ISS is very different from doing so on Earth, Muotri said. For example, you're limited by the amount of lab equipment you can have and there's always a risk that the rocket launch will be canceled at the last minute, he said. Returning the organoids to Earth can also be quite "perilous," Jamieson said, as the load carried by the spacecraft often lands in the ocean. 

Nevertheless, the experts hope to use these organoids to surpass new frontiers of discovery. 

"I'm excited about working in space," Jamieson said. "I think this is a literal cancer moonshot, and we've found a cancer kill switch." 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Extremely realistic-looking prosthetic eyes can now be 3D-printed in a fraction of the time it would normally take to produce the eyes by hand, scientists demonstrate in a new study.

This 3D-printing technology could be used to help create realistic prosthetic eyes for the 8 million people worldwide who need at least one, either due to a birth defect that causes an eye to be small or missing or because they've lost an eye.

The new technology can create a prosthetic eye in just 90 minutes, compared with the eight hours it would normally take a skilled technician, or ocularist, to produce one by hand. The 3D-printed eyes require five times less labor to make than traditional methods, the scientists behind the technology wrote in a new paper published Tuesday (Feb. 27) in the journal Nature Communications. 

The 3D-printed eyes also look more natural than traditional prostheses; this could help improve a patient's self-confidence in using the devices. 

"Patients are very conscious about wearing a prosthesis, and they don't want others to notice," Johann Reinhard, lead study author and a researcher at the Fraunhofer Institute for Computer Graphics Research in Germany, told Live Science. "With these more realistic eyes, it might help them to participate more in society," he said.  

Related: Scientists develop 'crying' model of human eye tissue

So far, this approach has been used to create prosthetic eyes for more than 200 adult patients at the Moorfields Eye Hospital (MEH) in London, including 10 people who were described in detail in the new study, Reinhard said. 

Normally, to craft a prosthetic eye, an ocularist makes a mold of the patient's eye socket by temporarily filling the cavity with a soft molding material. That material is then removed and used as a template to make a wax impression that can fit in the person's eye socket. The wax is smoothed, tested and reshaped until it fits comfortably and is then used to make a plastic version. The final, plastic eye is hand-painted to match the patient's healthy eye. 

Such artificial eyes usually have to be replaced every five to 10 years, in part due to wear and tear to the plastic that they're made of. However, because this is a manual process, there's always a chance that subsequent eyes produced for the same person could differ in their appearance and shape. 

Instead, the new printing approach involves taking a specialized image of a patient's empty eye socket and of their healthy eye. These images are then processed and used to draft blueprints that can be sent to be 3D-printed in the lab. This printing process usually takes around 90 minutes, but it can be sped up if multiple eyes are printed at once — for instance, it would take just 10 hours to print 100 prosthetic eyes, Reinhard said.  

These 3D-printed eyes closely replicate the color, size and structure of the patient's healthy eye and are particularly good at capturing the colored part of the eye, known as the iris, and the white part of the eye, called the sclera. Once finished, the eyes take 15 to 30 minutes to be installed by an ocularist, Reinhard said. 

About 80% of adults in need of prosthetic eyes could theoretically have one made this way, the team said. However, this wouldn't be possible for all patients, such as those who have a very complex eye socket, as the software wouldn't be able to find a matching shape for the prosthetic eye, Reinhard said. 

More data are needed to see if this technique could also be used to make prosthetic eyes for children, which would require more regulation, Reinhard said. 

For now, though, the team intends to test the approach in more clinics. Sometime this year, they hope to publish the results of a clinical trial that explored the long-term performance of these 3D-printed eyes in 40 patients at MEH, compared with the performance of manually made prostheses. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

For the first time, scientists enabled an amputee to feel temperature via his prosthetic hand, crossing what the researchers say is one of the final hurdles in being able to imbue prosthetics with the full spectrum of senses available in a human limb. 

The team achieved this feat by implanting a small device in the patient's prosthetic hand. This included a temperature sensor that was placed at the tip of the index finger and was linked to an apparatus, or thermode, connected to what remained of the patient's arm. This created a feedback loop in which temperature changes detected by the sensor were relayed to the patient's central nervous system; the brain then interpreted the temperature changes as being "felt" in the missing hand. 

Fabrizio, a 57-year-old man from Italy whose last name has not been disclosed for privacy reasons, had his right arm amputated below his elbow when he was 20 years old and was the first person to receive the new device. Over more than a year, he participated in lab experiments that ultimately demonstrated the temperature-sensing abilities of his modified prosthetic limb.

In one experiment, for instance, Fabrizio successfully distinguished between visually identical bottles of water that ranged from 104 degrees Fahrenheit (40 degrees Celsius) to 68 F (20 C). He correctly distinguished the temperatures every time he used the new device, compared with 33% of the time when it was switched off. 

In another test, he sorted metal cubes of different temperatures much more quickly with the device than without it. Another time, while blindfolded, Fabrizio differentiated between a human arm and a prosthetic arm just by poking them — in 80% of tests with the device, compared with 60% without the device. 

Related: Oldest medical amputation on record was performed on a Stone Age child in Borneo 31,000 years ago 

The researchers behind the new device described their findings in a paper published Friday (Feb. 9) in the journal Med. They say the invention both serves a helpful function and could make amputees' lives more enjoyable. 

"We tend to underestimate the importance of the hand as a way of interacting effectively with other people," Silvestro Micera, co-senior study author and a professor of translational neuroengineering at the Swiss Federal Institute of Technology Lausanne, told Live Science. 

"What was really cool to see was that Fabrizio once, by chance, was touched by the arm of one of the students [in the lab] and he said, 'Wow, this is human,'" Micera said. "So the cool thing is that you can get the feeling that you are touching another human being."

Over the years, advances in technology have improved the touch-sensing ability of prosthetic limbs. However, temperature perception has been challenging to replicate artificially.

In 2023, Micera and colleagues discovered that people who had parts of their arms removed could still detect different temperatures applied to the skin on their residual limbs. It's also well known that amputees often continue to sense their lost limb as if it were still there — a phenomenon called a "phantom limb." 

The team developed a way to tap into that remaining sensation and then embedded this technology into a commercial prosthetic limb. That's why they tested the device with Fabrizio, who already had a prosthetic and had also participated in the original 2023 study. 

The "beauty" of the device, Micera said, is that you don't need to change an amputee's prosthetic limb. Theoretically, it could be integrated into any commercial prosthesis without requiring surgery to install it. The device is also battery-powered so it doesn't need to be plugged in, making it more readily wearable.

"Devices that create more natural ways for patients to interact with the environment are needed," Jeroen Bergmann, an associate professor of engineering science at the University of Oxford in the U.K., who was not involved in the research, told Live Science in an email. "This work shows a promising approach to address this need, but more work is needed to truly make this suitable for real world application," he said. 

Warren Grill, a professor of biomedical engineering at Duke University in North Carolina who was also not involved in the research, echoed Bergmann's comments. He said to Live Science in an email that the findings were an "exciting advance in the development of a sensorized prosthesis" but that more research is needed in an everyday setting. 

Such assessment will provide more insight into the benefits that the device may offer patients, Leen Jabban, a lecturer in electronic and electrical engineering at the University of Bath in the U.K, who was also not involved in the research, told Live Science in a separate email. 

The team is now refining the device — for instance, they want to see how its performance might be affected by factors such as air temperature and humidity. Soon, they hope to develop a prosthesis that restores all of the sensation that can be felt in the human hand and that can be used at home. They aim to initially test the device in two volunteers. 

"Hopefully, in say, three years from now, there will be two people getting these prostheses at home for good, with the possibility of getting all the sensation we normally have day by day from our natural hand," Micera said. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

In a rare case, a girl's stomach folded over on itself, leaving her in crippling pain for two days and in need of emergency medical treatment.

The 12-year-old girl in Ethiopia had developed a rare and potentially life-threatening condition called gastric volvulus, in which all or part of the stomach rotates by more than 180 degrees. This caused her abdomen to become tender and swollen and stopped her from being able to pass stools or breathe properly.

Gastric volvulus kills between 30% and 50% of the patients it affects. It can cause the stomach to become completely obstructed, blocking the movement of food through the organ as well as the flow of blood and oxygen to the stomach and back to the heart, which can result in tissue death. Holes can also form in the folded stomach, causing blood and other fluids to leak out. This makes it even harder for the heart to pump blood around the body and can also lead to blood poisoning.

In the recent case, the girl survived the painful condition thanks to prompt diagnosis and surgical treatment, according to a report of her case, published Jan. 13 in the International Journal of Surgery Case Reports.

Related: 'Complete' twist of fallopian tube sent girl to hospital with sudden belly pain

First described in 1886, gastric volvulus is most often diagnosed in people over the age of 50 or in children under age 1. Although researchers aren't sure exactly how many people experience the condition, it is believed to be extremely rare, with the total number of reported cases running in the hundreds worldwide.

The condition is most commonly caused by a paraesophageal hernia, in which part of the stomach pushes into the chest cavity through an opening in the diaphragm — the dome-shaped muscle that supports the expansion and contraction of the chest during breathing. These hernias, which can be caused by structural abnormalities during development or by traumatic injuries to the diaphragm, can make the stomach vulnerable to twisting.

In the girl's case, her gastric volvulus resulted from the stomach folding over on itself like a clam shell shutting, which occurs in about one-third of patients with gastric volvulus. Such cases are more likely to be seen in young children and are caused by looseness in the ligaments that normally anchor the stomach in the abdomen, the authors wrote in the case report. Specifically, the ligaments that attached the girl's stomach to the horizontal, middle portion of her large intestine were unstable, they wrote.

Gastric volvulus is normally diagnosed using imaging techniques, such as computed tomography (CT) scans or X-rays. However, in the girl's case, the CT scanner in the hospital wasn't working, the case report authors noted. After initial examinations of her abdomen, doctors rushed the girl straight to the operating theater without doing any imaging and diagnosed her in the course of surgery.

Once diagnosed, gastric volvulus is usually treated by surgically untwisting the stomach and securing it to the abdominal wall to prevent any future folding. In high-risk cases, doctors may also relieve the pressure in a patient's stomach using a tube inserted through their nose, as was the case with the girl in this report.

Six days after her surgery, she was able to leave the hospital.

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Scientists have created the first 3D model of the human conjunctiva — the clear, protective outer membrane of the eye — in the lab, and it even produces its own tears.

The researchers say the new model could be used to study diseases that affect millions of people, such as conjunctivitis, better known as "pink eye." 

The replica conjunctiva is an "organoid" — a lab-grown mass of cells made to resemble 3D, miniature versions of full-size tissues in the body. Organoids are typically grown from stem cells and enable scientists to recreate the structure and function of human organs. Because of this, the models are emerging as promising alternatives to using animals for drug testing. 

Until now, there have been no realistic lab models of the human conjunctiva, which has limited research in the field, the scientists behind the new organoid noted. The team reported their findings in a study published Jan. 11 in the journal Cell Stem Cell. 

Related: In a 1st, 'minibrains' grown from fetal brain tissue

To make the new model, the study authors collected stem cells from conjunctival tissue provided by organ donors and patients who were undergoing eye surgery. Using chemicals called growth factors, the scientists coaxed the cells into 3D structures that mimicked the human conjunctiva. 

These organoids contained all the cells normally found in the conjunctiva, including mucus-producing cells, such as goblet cells and keratinocytes, which enable the tissue to make mucus-rich tears that protect and lubricate the surface of the eye. However, the study authors found that the latter cells also secreted antimicrobial proteins.

"We discovered that the conjunctiva makes antimicrobial components and therefore contributes to tear production in more ways than by simply making mucus," study first author Marie Bannier-Hélaouët, a postdoctoral researcher in developmental biology and stem cell research at the Hubrecht Institute in the Netherlands, said in a statement.

The new model mimicked all the major features of the human conjunctiva, including its ability to produce mucus-rich tears. In addition to revealing these antimicrobial properties of keratinocytes, the model helped the scientists identify tuft cells, a type of cell not previously known to be in the conjunctiva. These are epithelial cells found in tissues that cover different surfaces of the body and have previously been linked to allergies. 

"Similar cells have been discovered in other tissues, but not in the human conjunctiva," Bannier-Hélaouët said.

The authors experimented with the new organoids by applying inflammatory chemicals called interleukins to the models to imitate what would happen during an allergic reaction.

"The organoids started to produce completely different tears: there was more mucus but there were also more antimicrobial components," Bannier-Hélaouët said. The newly discovered tuft cells also became more abundant within the organoid, suggesting they may influence how our eyes respond to allergies, according to the statement.

The authors intend the model to be used to test new drugs to treat diseases of the conjunctiva, including dry eye, which is caused by a poor quantity or quality of tears, and pink eye, or inflammation triggered by an infection, allergies or irritants. 

In the study, the researchers infected the organoids with various viruses that are known to cause viral conjunctivitis and then treated the infections with drugs. For example, infection with herpes simplex virus 1, which is mainly responsible for oral and genital herpes but can also cause conjunctivitis, was reversed using antiviral medications. 

More research is needed, but the authors hope to one day use this approach to make replacement conjunctivae for people with eye burns, cancer or genetic disorders, according to the statement. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website! 

Wrinkles are a telltale sign of aging, but not everyone develops them at the same rate. Some people get their first wrinkles in their early 20s, while others may boast a smooth-faced, youthful look well into old age.

So why do wrinkles form, exactly?

There is no single answer to this question, because human skin is a complex organ and many factors can affect its appearance, Dr. Debra Jaliman, a board-certified dermatologist based in New York and a member of the American Academy of Dermatology, told Live Science.

The skin is composed of multiple sheets of tissue divided into three layers: the epidermis on top, the dermis in the middle, and the hypodermis at the bottom. The dermis is much thicker than the epidermis and the hypodermis, as it contains nerves, blood vessels, sweat glands, hair follicles and proteins that support the skin's overall structure. Specifically, it's mostly made up of the fibrous proteins collagen and elastin, which are suspended in a gooey matrix.

Related: Why does hair turn gray?

Wrinkles start to appear as these structural components of the dermis start to degrade, a process broadly known as skin aging. However, exactly when the age-related creases develop depends on a combination of factors, including a person's genetics and lifestyle, Jaliman said.

In general, as we get older, the number of cells in the skin that produce collagen and elastin, known as fibroblasts, begins to decrease and the remaining fibroblasts become less productive, Dr. Ginni Mansberg, a Sydney-based primary care physician and the medical director of Evidence Skincare, told Live Science by email.

In addition, with age, existing structural proteins in the skin are broken down by enzymes at a higher rate than they were in the past. Aging also causes the top layer of the skin's epidermis, called the stratum corneum, to become thinner. This structural shift makes it more difficult for the skin to retain moisture, and dry skin makes any wrinkles more visible, Mansberg said.

Another aspect of aging that may drive wrinkle formation is cellular senescence — a zombie-like state damaged cells enter when they don't die off when they normally would. Instead of being removed or repaired, more of these zombie cells accumulate in the skin with age, releasing chemicals that can fuel the degradation of skin's structural components.

The overall number of senescent cells in the body increases with age, but that's not the only factor that can lead to this shift. Senescence can be triggered by inflammation and DNA damage, for example, according to a 2021 review published in the journal Ageing Research Reviews.

The rate at which aging drives wrinkle formation depends on additional factors, such as our genetic makeup.

"For example, people with lighter skin tones will find that their skin ages faster than people with darker skin," Jaliman said. That's because the same genes involved in skin color can also influence the skin aging process. This is partly due to genes related to the protective skin pigment melanin, but also genes that contribute to wrinkles through melanin-independent pathways that are not yet fully understood, according to a 2022 review in the journal Scientific Reports.

Unlike genetics, some factors that contribute to wrinkle formation are within our control. For example, excessive sun exposure can accelerate skin aging, because the sun's ultraviolet rays cause inflammation and DNA damage in skin cells, Mansberg said. This can drive not only wrinkle formation but also skin cancer, which is why sunscreen is so important.

Being exposed to air pollution and smoking cigarettes can also fuel the formation of wrinkles by inducing oxidative stress, a state of imbalance between cells' production and elimination of harmful molecules called free radicals, Jaliman noted.

Free radicals are byproducts of the breakdown of oxygen in the body. If they are not counteracted by antioxidants, either produced in the body or ingested, these highly reactive particles can damage the skin's structural components. Therefore, a diet rich in foods that contain high levels of antioxidants, such as fruit and vegetables, may somewhat help to slow the formation of wrinkles, Jaliman said.

However, you are bound to get wrinkles eventually, regardless of what you eat or what cosmetics you use to slow down the aging process.

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

You get ready to leave the cozy warmth of your house and brace for the winter's harsh weather — and, of course, you can't step foot outside without pocketing your trusted lip balm.

But have you ever wondered why your lips get dry in the winter?

The answer lies in lips' unique anatomy, Dr. Luke Powles, a London-based physician and associate clinical director for Bupa Health Clinics, told Live Science in an email. "The skin on your lips has a thinner protective barrier compared to the rest of the skin on your face, which makes it more susceptible to dehydration," he said.

Starting at the "vermillion border" — the often-sharp line that demarcates lip tissue from the rest of the face — the tissue resembles the mucous membrane that lines the inside of the mouth. It consists of only three to five layers of tissue and does not contain any of the hair follicles or sweat glands found elsewhere on the face, according to the medical resource StatPearls.

Related: Can lip balm make your chapped lips worse?

In fact, "the cellular layers of skin on your face are up to six times thicker than found on your lips," Powles said. "Your lips also have fewer oil glands compared to other parts of the body."

This comes into play during the winter, when the air outside gets colder and less humid and people switch on the heat in their homes and businesses. This continuous exposure to dry air dehydrates the delicate skin of the lips, causing it to crack, peel and bleed — a condition scientifically known as common cheilitis, Powles said.

While it's tempting to try to ease the discomfort of common cheilitis by licking your lips — and we sometimes do this without thinking — this may actually aggravate the problem. That's because saliva contains digestive enzymes, such as amylase, which breaks down starches into sugars, and lipase, which aids the digestion of fats.

"When you lick your lips, the dried saliva removes the natural oily protective layer that helps keep your lips healthy," Powles said. Over time, these enzymes can damage the lip skin itself and contribute to dehydration.

Having a stuffy nose — a hallmark of the winter cold and flu season — can also expose the lips to excess saliva by forcing a person to breathe through their mouth, according to a 2020 review in the International Journal of Women's Dermatology.

Dry lips are not only an aesthetic issue but also a medical one. For example, chapping can leave lip skin more prone to infections that penetrate the skin barrier, Nina Prisk, an aesthetics nurse prescriber at Update Aesthetics clinic in London, told Live Science by email. Microbes such as the bacterium Staphylococcus aureus or yeast Candida albicans can fuel inflammation in the lips and thus aggravate the symptoms of cheilitis, according to a 2018 review published in the journal Acta Clinica Croatica.

If your chapped lips don't improve when you use lip balms, ointments or a humidifier, it may be worth speaking with a medical provider about more advanced treatments, Cleveland Clinic advises.

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

A strange dolphin in the Gulf of Corinth has developed intriguing, hook-shaped "thumbs" carved out of its flippers, photographs show.

Researchers with the Pelagos Cetacean Research Institute spotted the dolphin on two occasions this summer during boat surveys off the coast of Greece. Despite the unusual appearance of its flippers, the animal kept pace with the rest of its pod and was seen "swimming, leaping, bow-riding, playing" with other dolphins, said Alexandros Frantzis, the scientific coordinator and president of the Pelagos Cetacean Research Institute.

"It was the very first time we saw this surprising flipper morphology in 30 years of surveys in the open sea and also in studies while monitoring all the stranded dolphins along the coasts of Greece for 30 years," Frantzis, who took the pictures of the thumbed dolphin, told Live Science in an email.

The Gulf of Corinth is a semi-enclosed pocket of the Ionian Sea, sandwiched between the Greek mainland and the Peloponnese peninsula. It is home to a unique mixed-species society of dolphins that includes common dolphins (Delphinus delphis), Risso's dolphins (Grampus griseus) and striped dolphins (Stenella coeruleoalba). The thumbed specimen was a striped dolphin, Frantzis said.

Related: Watch a huge megapod of acrobatic spinner dolphins in incredible, rare video

Around 1,300 striped dolphins live in the Gulf of Corinth, where they are isolated from the rest of the Mediterranean population. The unusual flipper "does not look like illness at all," Frantzis said. Instead, it may be "the expression of some rare and 'irregular' genes" that cropped up due to constant interbreeding, he said.

Lisa Noelle Cooper, an associate professor of mammalian anatomy and neurobiology at the Northeast Ohio Medical University, agreed that the dolphin's defect is likely rooted in its genes. "I've never seen a flipper of a cetacean that had this shape," Cooper told Live Science in an email. "Given that the defect is in both the left and right flippers, it is probably the result of an altered genetic program that sculpts the flipper during development as a calf." 

Cetaceans — a group of marine mammals that includes whales, dolphins and porpoises — have evolved distinct forelimbs with more phalanges, or finger bones, compared with other mammals. These bones are arranged into human-like "hands" encased in a soft-tissue flipper, said Bruna Farina, a doctoral student specializing in paleobiology and macroevolution at the University of Fribourg in Switzerland.

This means dolphins have thumbs, although they aren't as prominent as ours and are concealed by their flippers, Farina told Live Science in an email.

Unlike in humans, whose fingers are fused into paddle-shaped hands in the womb with cells that die off before we are born, cells accumulate around dolphins' forelimb bones to form flippers, Cooper said. "Normally, dolphins develop their fingers within the flipper and no cells between the fingers die off," she said.

But the dolphin photographed in the Gulf of Corinth appears to be missing fingers and some of the tissue that would usually encase them. "It looks to me like the cells that normally would have formed the equivalent of our index and middle fingers died off in a strange event when the flipper was forming while the calf was still in the womb," Cooper said.

The dolphin's thumb and fourth digit, however, remained. "The hook-shaped 'thumb' may have some bone inside of it, but it certainly isn't mobile," Cooper said, adding that "no cetaceans have mobile thumbs." 

"It is lovely to see that this animal is thriving," Cooper added.

Your skeletal muscles are attached to your bones by tendons, and they enable you to move around and maintain an upright posture. Some muscles, such as those that help you smile or flex your fingers, are only a few inches long, while others, like those in your thighs, are big and bulky.

But have you ever wondered which muscle is the largest and which is the smallest?

The answers depend on whether the muscles are measured by mass or by surface area.

The gluteus maximus is the largest muscle in the body by mass, D. Ceri Davies, former president of the Anatomical Society in the U.K., told Live Science by email. The best known of the glute muscles, the gluteus maximus runs diagonally from the top center of the pelvis to the femur, or thigh bone. It accounts for about 12% to 13% of the total weight of all the leg muscles, according to a study of adult cadavers.

"The gluteus maximus extends the thigh at the hip joint," Davies said. "We use it when we get up from a chair, walking up steps or uphill. It needs to be powerful to move the weight of the entire upper body."

Related: Why is it harder for some people to build muscle than others?

Of course, training in sports that require ample glute power — like sprinting — can increase the size of the gluteus maximus. One small study found that the absolute volume of elite sprinters' glutei maximi was about 45% greater than that of sub-elite sprinters.

And interestingly, the human gluteus maximus muscle is bigger than that of apes and monkeys, at least relative to overall body size. Some scientists propose that its great size may be an evolutionary adaptation to certain demands posed by being bipedal, meaning upright on two legs. For example, the gluteus maximus is critical to humans' ability to climb stairs and run while upright.

The latissimus dorsi, commonly called the "lats," are the largest muscles in the human body in terms of surface area, Davies said.

There are two triangle-shaped latissimi dorsi — one on each side of the spine. These broad, flat muscles sit on top of the other muscles of the mid- and lower back. According to a 2022 study in the International Journal of Morphology, an average adult latissimus dorsi measures about 7 inches (18 centimeters) in width and 14 inches (36 cm) in length. That said, it's only about half an inch (1.3 cm) thick.

On the opposite side of the muscle-size spectrum is the stapedius, a tiny muscle inside the ear. Measuring roughly 0.2 inch (5 millimeters) in length, it is the smallest skeletal muscle in the human body.

"The stapedius attaches to the stapes, one of the small bones in the middle ear that carry sound vibrations from the eardrum to the auditory nerve," Davies said. "Contraction of [the] stapedius dampens the movement of the stapes, preventing nerve damage resulting from loud noise."

In other words, the teensy muscle stabilizes the stapes to keep it from vibrating too violently. The muscle involuntarily contracts in response to sounds of a particular volume — but if it only responds to extremely loud sounds or it doesn't contract at all, that can be a sign of hearing loss. So even though the stapedius is puny, it performs an important job.

This article is for informational purposes only and is not meant to offer medical advice.

Cells are the building blocks that form all the tissues and organs of the body — and now, scientists have an estimate of just how many individual cells the human body contains.

According to a new analysis of more than 1,500 papers, the average adult male human has around 36 trillion cells — that's 36 followed by 12 zeros — while adult females have 28 trillion and 10-year-old children have about 17 trillion. To arrive at these estimates, the authors of the new study, which was published Monday (Sept. 18) in the journal PNAS, considered the size and number of 400 types of cells in the body across 60 tissues, including muscle, nerve and immune cells. 

Although scientists have estimated a similar number of cells — between 30 and 37 trillion — in adult male humans before, until now, the relationship between cell size and number hadn't been studied across the whole body, according to the authors. 

"We were surprised to see a fairly regular inverse relation between the size and count of cells across the whole human body," Ian Hatton, lead study author from the Max Planck Institute for Mathematics in the Sciences in Leipzig, Germany told Live Science in an email. In other words, there is a "trade-off" between cell size and number, so the larger the cell, the lower their overall number relative to smaller cells. That means, if cells are grouped by size, each group contributes the same amount to the overall mass of the body. 

Related: Does the human body replace itself every 7 years?

"This pattern spans seven orders of magnitude in cell size, from the tiny red blood cells to the largest muscle cells, comparable to the mass ratio of a shrew to a blue whale," Hatton said. 

The authors acknowledged several limitations of the study. For example, they focused on "average" adults' and children's bodies. Their benchmark adult male weighs 154 pounds (70 kilograms), the adult female weighs 132 pounds (60 kg) and the child weighs 70 pounds (32 kg), based on reference figures from the International Commission on Radiological Protection. This notably doesn't reflect the huge variation in size and weight that exists between humans. 

"There is of course large variation between different anatomical models," Hatton said. "But other than the variation in fat and muscle content in the adipocytes [fat cells] and myocytes [muscle cells], much of the variation is probably not significant relative to the other sources of error that is associated with trying to put bounds on the many trillions of cells in the human body," he said. 

Indeed, the study authors explained that there may be a lot of uncertainty in their figures. In many cases, they had to rely on inferences about the dimensions of cells made using microscopy and other indirect measurements, rather than direct measurements of the mass of different cell types. They also estimated total cell numbers for adult females and children using papers that mainly considered adult males, study author Eric Galbraith, a professor and group leader at McGill University in Canada, told New Scientist. 

"There's unfortunately still more information for reference males than females or children," he told New Scientist.

Further research is needed to fill these gaps, but for now, Hatton told Live Science that the study highlighted several discrepancies in cell counts proposed in prior work, which could have potential health implications.

"Possibly most critical is our estimate of the total number of human lymphocytes, which are vital for our immune function," he said. "We estimate 2 trillion lymphocytes in the human body which is four times higher than prior estimates and could prove important in lymphocyte-related health and disease, such as HIV or leukemia." HIV and AIDS weaken the immune system by destroying certain lymphocytes, while leukemia is a cancer that affects the immune cells.

Data from the new study can be freely accessed online.

Humans have ape ancestors to thank for their flexible shoulders and elbows, which may have evolved as a natural braking mechanism for tree-scaling.

Scientists made the discovery while watching numerous videos of chimpanzees (Pan troglodytes) and sooty mangabey (Cercocebus atys) monkeys, which are much more distantly related to both chimps and humans, climb up and down trees in the wild. 

In the new study, the researchers noticed that although both animals ascended trees similarly with their shoulders and elbows closely bent toward their bodies as they swiftly reached from one branch to the next, they differed in their techniques for descending.

The findings suggest that chimps and humans may have flexible shoulder and elbow joints as a way to "counteract" the effects of gravity on their heavier lower bodies. The result was a finely calibrated braking system that decreased their risk of falling while they descended downward high in the treetops, according to the study, published Sept. 6 in the journal Royal Society Open Science.

While mangabeys were less flexible, the chimps extended their arms above their heads while descending — similar to the way a person goes down a ladder. This maneuver was a way for the primates to slow their descents as gravity pulled them downward, the team said in a statement. 

"[We] noticed that while both chimpanzees and mangabeys climbed trees in a clipped motion where they didn't fully extend their joints, in downclimbing the mangabeys continued this clipped motion, while the chimps did not," co-author Mary Joy, a biological anthropology major who graduated from Dartmouth University in 2021 and made this her undergraduate thesis, told Live Science. "The two had very different ranges of motions."

Related: Wild chimps and gorillas can form social bonds that last for decades

Human and chimpanzee ancestors diverged approximately 6 million to 7 million years ago, while the mangabey's monkey ancestor diverged from apes around 30 million years ago.

But the study suggests that flexible appendages had evolved by the time of the last common ancestor between chimps and humans, but after apes and monkeys diverged. This flexibility would have proven beneficial for things that involved specific movements like gathering food, hunting and defending themselves, according to the study.

This marks the first time researchers have extensively studied how great apes descended trees; previously, most studies were focused on them climbing.

"We knew generally that chimps had an increased range of motion in their shoulders and elbows, while mangabeys did not," Joy said.

This is because mangabeys and other monkeys are built similarly to quadrupedal mammals like cats and dogs, which walk on all fours and have "deep, pear-shaped shoulder sockets," the team said in the statement. The inner crook of their elbows also protrudes, making the joint resemble the letter "L," according to the statement. These joints may offer stability, but they lack a good range of motion.

Upon analyzing the joints in existing chimp skeletons that were part of museum collections, researchers noticed that the angle of the apes' shoulders was 14 degrees greater when they were descending versus when they were climbing. Their arms also extended outward at the elbow 34 degrees more when the chimps were going down trees, according to the study.

This change in motion not only helped the chimps slow the pull of gravity but also allowed them to decelerate safely.

"Chimps can get out of trees and climb downward without having to keep their shoulder and elbow muscles under tension, which results in the exertion of a lot of energy," Joy said. "As humans, the introduction of this increased range of motion had a lot of benefits, like letting us raise our arms above our heads or throwing a ball. This motion is a legacy of evolutionary pressure on our ancestors, which gave us the ability to do a lot of things."

Eyes are among the most unique organs in the body. They enable us to see the world around us, to convey our emotions and even be recognized by biometrics. But what are eyes actually made of?

To explain, let's begin by looking at the key structures of the eye.

"The similarities [in terms of structure] are more like a camera," Dr. Parwez Hossain, a professor of ophthalmology at the University of Southampton in the U.K., told Live Science. "You have the frontal optical system which consists of the cornea and the lens, and the photosensitive area, which is called the retina."

The cornea is the smooth front surface of the eye that covers the lens and focuses most of the light that hits the eye onto the retina at the back of the eye, he said. The cornea is predominantly made up of a protein called collagen, which is arranged in a very regular pattern that helps light pass through the eye. Collagen also strengthens the eye, which is important because this region is very exposed and therefore vulnerable to damage. 

Related: How do screens damage your eyes?

Behind the cornea is the lens that focuses the rest of the light that enters the eye onto the retina. The lens is made up of proteins that maintain its transparency and make it flexible so that it can change shape and thus enable us to see objects that are either near or far away.

According to Hossain, the retina can be likened to photographic film. It is composed of 10 distinct layers of nerve cells, or neurons, including rod and cone photoreceptor cells that react to light. When illuminated, these cells generate electrical impulses. These then travel down the optic nerve, which is behind the eye, and pass into the brain, where they are interpreted as vision. 

Many other structures in the eye also support vision, Hossain said. These include the conjunctiva, which is a clear, thin protective outer membrane that lines the inside of the eyelids and covers the white part of the eye called the sclera — another protective region which helps maintain the shape of the eye. 

There is also the colored part of the eye known as the iris, which is made up of muscle that controls the size of the pupil, the black spot within the iris that enables light to pass through to the lens. The color of the iris depends on how much of a pigment called melanin it contains. Fluids, such as the vitreous humor and the aqueous humor, maintain the round shape of the eye and nourish it, respectively. 

Related: What are tears made of? 

As we age, the composition and structure of the eyes change. One of the main areas where this happens is in the lens. 

"As we get older, the lens stiffens and loses its ability to change shape during focusing and by middle age this loss of focusing ability means that we need reading glasses for near focus," John Lawrenson, a professor of clinical visual science at City, University of London, told Live Science in an email.

The lens also becomes less transparent and can develop "cloudy" areas called cataracts, Lawrenson said. More than half of Americans over the age of 80 have had cataracts at some point. Although most cataracts are linked to aging, other risk factors include having diabetes and smoking. 

Another common age-related eye disease is age-related macular degeneration (AMD), Lawrenson said, which occurs in the central area of the retina called the macula.

"Because lens cells and retinal cells do not renew themselves, the lens and retina are most susceptible to damage with age," Lawrenson said. "Exposure to UV light and high oxygen levels in the eye create conditions that can lead to cellular damage." 

This article is for informational purposes only and is not meant to offer medical advice.

They rise up in our eyes when we're mourning the loss of a loved one, getting the "feels" from a touching scene in a rom-com or simply chopping onions for dinner: Tears, whether you shed them often or hardly at all, are a ubiquitous part of the human experience. 

You may think of tears as just water — after all, as Justin Timberlake demonstrated in his hit song "Cry Me a River," these droplets of sadness are often likened to bodies of water, raindrops or even storms. 

But what are tears actually made of?

It turns out that there are three distinct types of tears, which vary in their composition, Daniela Oehring, an associate professor of optometry at the University of Plymouth in the U.K., told Live Science.

Related: Vlad the Impaler may have cried tears of blood, chemical analysis of his letters finds 

You're probably most familiar with the emotional tears that people shed in sadness after a breakup or in joy when seeing a friend after years spent apart. But humans produce two other types of tears: basal tears, which cushion the eye, supply the tissue with nutrients and remove debris; and reflex tears, which are produced in response to irritants, such as smoke or the chemicals released when you chop an onion.

Basal tears have lots of salt ions and other electrolytes, as well as proteins with antimicrobial properties, Oehring said. These proteins include lipocalin, which binds and disrupts certain compounds in microbes, and lysozyme, an enzyme that kills bacteria by breaking down their cell walls, she said. 

Reflex and emotional tears, on the other hand, have a higher water content, and a lower concentration of fats and proteins, than basal tears do. Some scientists have reported that, compared with reflex tears, emotional tears carry higher concentrations of hormones typically released when the body is under stress.

Upon being made, all these tears are added to a thin film that covers and nourishes the cornea, the transparent tissue over the front of the eye. This tear film has three distinct layers. On the outside is an oily layer produced by the meibomian glands in the eyelids that stops the eyes from drying out. The next layer is watery and lubricates the eye; it's made mostly by the lacrimal gland, which also adds proteins, oxygen and electrolytes. The inner layer, closest to the cornea's surface, contains a slime-like protein called mucin, which helps the tear film stick to the eye's surface.

According to Oehring, people produce about 1 to 4 microliters of tears a minute — or about 1.44 to 5.76 milliliters per day — on average. These are primarily basal tears, which shed constantly, rather than emotional and reflex tears made in response to stimuli. However, this volume can vary significantly depending on what you're doing.

"If you drive a bike, for example — and you have a lot of air, so you have a high evaporation rate — your tear production changes," she said. "If you are in a steam room, then your tear production decreases, because generally, there is no need to produce the water." Tears drain from the eyes via tear ducts. But because emotional and reflex tears are typically released in a flood, not in a trickle, these can often spill out of the eye rather than draining normally. 

If the quantity or quality of your tears declines such that your eyes don't stay lubricated, you may develop dry eye, which affects 16 million Americans. 

Many factors raise the risk of this common condition, Oehring said, including smoking, poor nutrition, and excessive time spent staring at computer screens and not blinking enough. As we age, we also become more susceptible to developing the condition, because our tear glands stop working as well. Some diseases can also increase the likelihood of having dry eyes, such as Sjögren's syndrome, an autoimmune condition in which the body's own immune cells damage the lacrimal glands that moisturize the eyes. 

People with Sjögren’s syndrome cannot even produce reflex tears. "Even if they get something in their eye, like an eyelash or something," Oehring said, "there is just not enough capacity to produce tears." 

This article is for informational purposes only and is not meant to offer medical advice.

You pull out your earphones and are confronted by a familiar, if icky, sight: earwax. All it seems to do is dirty your listening devices, block your ears, cause discomfort and — in severe cases — obstruct hearing. But could this gooey nuisance actually serve a beneficial purpose? 

The science tells us that the crud you wipe off your earphones is actually important for your ear health, and you may unwittingly harm yourself if you try to extract it.

Earwax is composed of dead skin cells mixed with secretions from oil and sweat glands in the ear. Skin cells in the outer ear canal originate at the center of the eardrum and then migrate toward the ear entrance, where they encounter a mixture of oils called sebum that moisturizes skin. Secreted by the so-called sebaceous glands attached to hair follicles, sebum mixes with secretions from sweat glands and shed skin cells to make earwax.

"Its purpose is to lubricate the skin in your ear canal to trap dirt and dust in the same way as the mucus up your nose," Kevin Munro, a professor of audiology at the University of Manchester in the U.K., told Live Science.

Related: Earwax may reveal how stressed you are

Sebaceous and sweat glands also secrete antimicrobial proteins into the mix, protecting the ear from bacterial and fungal infections. 

"Your ear canal is like a tunnel or cave," Munro said. "It can get warm and moist, and it's a nice environment for bacteria to grow." Extracted earwax has been shown in lab dishes to hinder the growth of common ear pathogens, such as the fungus Candida albicans and the bacteria Pseudomonas aeruginosa and Staphylococcus aureus. This may be due to the slightly acidic nature of earwax — the pH of which ranges from 5.2 to 7.0 — and the immune proteins it contains, including antibodies that latch onto foreign invaders and lysozyme, an enzyme that breaks down the cell walls of some bacteria.

Given earwax's helpful roles, people should avoid removing the sticky substance if it isn't causing any problems. People should seek medical attention if a buildup of earwax begins to cause pain, blockages or hearing difficulties, Dr. Satoshi Hara, an ear, nose and throat doctor and associate professor at Juntendo University in Japan, told Live Science in an email. 

Troublesome earwax buildup is most common in  people older than 60, because with age, the wax migrates out of the ear more slowly and a larger amount is produced, Munro said. Besides these age-related changes, wearing earphones, earplugs or hearing aids that block the exit of earwax can also lead to buildup. 

Munro cautioned that people should not attempt to remove earwax using cotton swabs, as these push wax further into the ear and can damage the eardrum. Ear candling, another inadvisable home remedy, involves placing a hollow, lit candle upright in the ear as the person lies on their side. The smoking candle allegedly suctions air and earwax out of the ear — but there's no evidence that the candle actually generates a vacuum, and it could lead to burns.

A doctor or pharmacist can safely remove earwax using a microsuction device or by flushing it out using an electronic water irrigator that ejects water into the ear at a low pressure. Medical providers typically avoid using syringes to flush out the ear, as this technique has punctured eardrums in the past by blasting the tissue with water under high pressure.

Patients can prepare for their earwax removal appointment by adding pretreatment drops, such as carbamide peroxide or medical-grade olive oil, to their ears for several days beforehand to soften the wax, Munro said.

This article is for informational purposes only and is not meant to offer medical advice.

An organ is a group of tissues that work together to perform a specific task in the body, such as digesting nutrients or producing chemical messengers that enable brain cells to communicate. Although scientists hold different views on what exactly counts as an organ, the most-cited number of organs in the human body stands at 78. These include major functional units like the brain and the heart, as well as much smaller body parts, such as the tongue.

Organs come in all shapes and sizes to reflect the myriad of important functions they perform. But which of the body's organs weigh the most? The answer to that question may surprise you.

These are 11 of the heaviest organs in the human body.

Related: 10 body parts that are useless in humans (or maybe not)

1. Skin

Skin wears the crown of the heaviest organ in the human body — however, there's some discrepancy as to how much it actually weighs. Some sources state that adults carry an average 8 pounds (3.6 kilograms) of skin, while other sources say that the skin makes up about 16% of an adult's total body weight, which would suggest that a 170-pound (77-kg) adult's skin would weigh about 27 pounds (12.3 kg), for example.

Why does this discrepancy exist? According to a 1949 report in the Journal of Investigative Dermatology, the larger of the two estimates counts the panniculus adiposus — a fatty tissue layer that lies between the top layers of the skin and the underlying muscle — as part of the skin, while the smaller estimate counts this tissue layer as separate. 

For what it's worth, the authors of the report argue against the inclusion of the panniculus adiposus and therefore conclude that skin makes up only about 6% of an adult's weight. But a modern medical reference text, the Primary Care Notebook, states that the fatty tissue is part of the third and deepest layer of skin, the hypodermis, which suggests it should be counted. 

2.  Femur

The skeleton is considered an organ system, or a group of organs that together perform specific physiological functions. One of the largest organ systems in the human body, the skeleton can weigh up to approximately 15% of an adult's total body weight, according to a 2019 review published in the International Journal of Biological Sciences.

The adult skeleton usually contains 206 bones, although some individuals may have additional ribs or vertebrae. The femur, a long bone located in between the knee and the hip, is the heaviest of them all, according to the medical resource StatPearls. On average, the femur weighs approximately 14 ounces (380 grams) — a bit less than one pound (0.4 kg) — but its exact weight varies depending on one's age, sex and health status, according to a 1974 review in the journal Acta Anatomica. 

3. Liver

Weighing around 3 to 3.5 pounds (1.4 to 1.6 kg), the liver is the second heaviest organ in the human body, according to the American Liver Foundation. 

The liver is a cone-shaped organ that sits on top of the stomach and beneath the diaphragm, the dome-shaped muscle located under the lungs. It helps break down toxins and digest food, among other vital functions. At any given moment, the liver holds about a pint (half a liter) of blood — about 13% of the adult body's blood supply, according to Johns Hopkins Medicine.

4. Brain

From reasoning to controlling movement, the human brain performs a myriad of vital functions in the body, and its weight reflects its importance. According to a commentary published in the journal PNAS, the brain accounts for about 2% of the average adult human's body weight. 

The brain's mass also depends on one's age and sex. At age 20, an average male's brain weighs 3 pounds (1.4 kg). By the age of 65, it drops to 2.86 pounds (1.3 kg). Female brains, on the other hand, tend to weigh around 10% less than that of males, according to the Encyclopedia of The Human Brain (Academic Press, 2002). However, when overall body weight is taken into account, men's brains tend to be only 0.2 pounds (100 g) heavier, according to a 1992 review published in the journal Intelligence.

5. Lungs

Lungs are among the heaviest organs in the human body. The right lung typically weighs about 1.4 pounds (0.6 kg), while the left lung is slightly smaller and weighs approximately 1.25 pounds (0.56 kg). In addition, male adults tend to have heavier lungs than female adults, according to Gray's Anatomy of the Human Body (Bartleby, 2000).

Interestingly, lungs weigh only 1.4 ounces (40 g) at birth. This organ is only fully developed when respiratory alveoli - the tiny branches of air tubes in the lungs - are fully formed. This happens at the age of 2, when lungs weigh approximately 6 ounces (170 g), according to the book Pediatric Critical Care (Mosby, 2011).

6. Heart

The human heart is at the center of the circulatory system. This vital organ tirelessly pumps the blood through the body, sending oxygen and nutrients into tissues and carrying waste products away from them. Heavy muscle fibers that power heart beats make up most of the heart’s impressive weight: around 10 to 12 ounces (280 to 340 g) in male adults and around 8 to 10 ounces (230 to 280 g) in female adults, according to Gray’s Anatomy of the Human Body.

7. Kidneys

Kidneys remove toxins and waste products from the body. This important task is done by nephrons, which are tiny structures that act as filters between the bloodstream and the bladder. Each kidney contains millions of nephrons, making this vital organ one of the heaviest in the body: about 4.5 to 6 ounces (125 to 170 g) in male adult and from 4 to 5.4 ounces (115 to 155 g) in female adult, according to the Gray’s Anatomy of the Human Body.

8. Spleen

Located in close proximity to the pancreas, the spleen removes old and damaged red blood cells from the bloodstream, regulates the circulating levels of white blood cells, a type of immune cell and produces antibodies, immune molecules that help fight infections. The spleen weighs on average 5 ounces (150 g) in adults, but this weight may vary between individuals, according to a 2019 review published in the journal Surgery.

9. Pancreas

The pancreas regulates blood sugar levels and secretes enzymes that help the intestines absorb nutrients from digested food. Alongside the spleen, it is one of the heaviest organs in the digestive system. The pancreas typically weighs from 2 to 3 ounces (60 to 100 g) in adults, according to Gray’s Anatomy of the Human Body. However, it can be as heavy as 6 ounces (180 g) in some individuals, according to a 1994 study published in the American Journal of Surgery.

10. Thyroid

The thyroid, a gland located in the neck, plays a key role in regulating the body's energy use. Its weight varies between individuals, but it usually weighs about an ounce (30 g). The thyroid gland may get heavier during menstruation and in pregnancy, according to Gray’s Anatomy of the Human Body. Hyperthyroidism, a medical condition that causes the thyroid gland to produce more hormones than the body needs, may also lead this organ to grow in size, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

11. Prostate gland

The prostate gland produces an alkaline fluid — meaning it has a pH greater than 7 — that is the primary component of semen. Despite its relatively small size, which is comparable to that of a walnut, the prostate is one of the heaviest organs in the human body.

An average adult prostate is around 0.8 ounces (25 g), but the organ's weight may vary from person to person. An enlarged prostate may grow to well over three times the average size and weight more than 2.8 ounces (80 g), according to the University of Utah.

Air sacs sandwiched inside the bones of the largest dinosaurs and pterosaurs to roam the Earth were so advantageous that these pockets might have evolved independently at least three times in different lineages, a new study finds.

Researchers already knew that these ancient giants had air bubbles in their bones. Now, evidence that some of the earliest dinosaurs on record lacked these air sacs suggests that they sprouted later, through convergent evolution, a phenomenon in which different organisms independently evolve similar traits.

Pterosaurs, meat-eating theropods and long-necked sauropods belong to a group of ancient reptiles called the avemetatarsalians, which are more closely related to present-day birds than to crocodiles. These three lineages evolved air-filled pockets in their bones, which kept their skeletons light and nimble. Without these structures, the beasts couldn't have grown so large or kept cool in the warm climate of the Triassic period (252 million to 201 million years ago).

"Less dense bones containing more air gave the dinosaurs and pterosaurs more oxygen circulating in their blood, as well as more agility to hunt, flee and fight, or even to fly," study first author Tito Aureliano, a researcher at the Institute of Geosciences at the University of Campinas in Brazil, said in a statement. "They not only used less energy but also kept their bodies cool more efficiently."

Related: Ginormous Jurassic fossil in Portugal may be the biggest dinosaur ever found in Europe 

Now, fresh evidence suggests that some of the oldest avemetatarsalians didn't have air sacs, which means that their relatives may have evolved hollow bones independently of one another.

In the study, published Dec. 9, 2022, in the journal Scientific Reports, researchers analyzed 233 million-year-old fossils from three early dinosaur species — the sauropodomorphs Buriolestes schultzi and Pampadromaeus barberenai and the meat-eater Gnathovorax cabreirai — that are among the "oldest good material" from sauropod dinosaurs and meat-eating herrerasaurid dinosaurs, Paul Barrett, a paleobiologist at the Natural History Museum in London who peer-reviewed the study, told Live Science.

"It shows that these complicated air sacs systems, in at least one branch of dinosaurs, only started to become really invasive [permeate the bones] much later in their evolutionary history than in the other two groups of reptiles that developed those systems," Barrett said.

The researchers made detailed micro-CT scans of the bones — unearthed between 2011 and 2019 in Rio Grande do Sul, Brazil's southernmost state — and detected small spaces in the vertebrae that could have housed blood vessels and marrow, but not air sacs.

The new study may help determine whether air sacs in sauropods, theropods and pterosaurs have the same evolutionary origin from a common ancestor, or whether they all achieved it independently through convergent evolution.

"What this study is suggesting is that those three groups may have achieved air sacs independently, because when we look at the earliest members of at least one of those groups, there's no good evidence for the air sacs," Barrett said.

A 2021 study suggested that ornithischians — a group of bird-hipped dinosaurs that lived in the Jurassic and Cretaceous periods (201 million to 66 million years ago) and breathed like weirdos — also lacked air sacs, despite sharing an ancestor with dinosaurs that developed air sacs. 

But the story of how air sacs evolved is riddled with uncertainties, according to Barrett. "Not all air sacs are in bones — some of those air sacs we know from living animals actually go between muscles and around organs," he said. "It might be that they all share air sacs and the air sacs are in their common ancestor, but they didn't leave any traces on the bone."

The fact that the researchers didn't find traces of air sacs in the oldest avemetatarsalians "still doesn't rule out that they might have had one that the fossils simply aren't telling us about," Barrett said. It may be that these ancient reptiles had air bubbles in their soft tissue that later penetrated the skeleton, an adaptation which lives on in birds today. 

If anyone has ever called you "the bee's knees," take it as a compliment! The phrase dates back to the 1920s and describes a "highly admired person or thing," according to the Merriam-Webster dictionary. 

But have you ever really stopped to imagine a bee with knees? Do bees — and other insects, for that matter — even have knees?

First, let's consider the knee we know best: our own. The human knee is a complicated structure. It includes three bones: the femur (thigh bone), tibia (shin bone) and patella (kneecap). But it's not just bones. An assortment of cartilage, ligaments and tendons, with the help of lubricants, all work in sync to help you straighten and bend your leg at the knee. Many other animals — such as birds, mammals and some reptiles — also have knees with kneecaps.

Related: What's the largest bone in the human body? (What about the smallest?)

Bees and their fellow insects, on the other hand, do not have bones in the sense that other animals do. Unlike vertebrates, which have hard skeletons that hold up their squishy outsides, bees and other insects are the opposite: A bee's skeleton, or exoskeleton, is on the outside. The exoskeleton, made of a tough material called chitin, protects its internal softer parts.

But similarly to the legs of humans and other legged animals, bees' legs are made up of distinct segments. According to Ramesh Sagili, a bee researcher at Oregon State University, bee legs are divided into five parts; starting closest to the body, they are the coxa, trochanter, femur, tibia and tarsus. 

In between the femur and the tibia, is there a knee like ours? The answer is no, according to Sagili.

"There will be a chitin joint [between] each of these segments," Sagili told Live Science. "Bees have six segments on the leg, and they are all joined together." 

Rather than a jumble of tendons, ligaments and a kneecap, bees have a simple ball-and-socket joint between their leg segments, Sagili said. Those joints help bees move their legs, groom themselves, dislodge pollen or dance to show their hive-mates where to find nectar-filled flowers.

In the early 20th century, before its evolution into a compliment, people used the phrase 'the bee's knees' to describe something that doesn't exist — and they were right. So, while bees don't have the same knees we do, they still have a joint between their tibia and femur that allows them some flexibility.

Does the human body contain any truly useless parts? Arguably, yes — but they might not be the ones you assume.

Some body parts, like the male nipple, arguably serve no useful function. But others, like the appendix, remain a matter of debate, as recent research suggests that they may serve a purpose scientists don't yet fully understand. 

Scientists have a track record of rating organs' importance before learning their true functions. But the more we learn, the more we realize many of those "useless" parts are actually essential. 

For example, in the 1890s, anatomist Robert Wiedersheim published a list of 86 human "vestiges," or body parts that had "lost their original physiological significance" to humans. The list, published in his book "The Structure of Man: An Index to His Past History," included essential anatomy, such as key valves in veins that help direct blood flow; the thymus gland, which makes disease-fighting white blood cells; and the hormone-producing pituitary and pineal glands.

Scientists continue to discover new things about the human body to this day. With that in mind, here are 10 of the human body's seemingly useless parts, some of which remain controversial.  

Related: How many organs are in the human body? 

1. Male nipples

In the womb, all human embryos initially develop all the same parts, and then about seven weeks in, the sexes begin to diverge, Michelle Moscova, leader of the Healthcare Innovations research team at the University of New South Wales Sydney, wrote in The Conversation. That's when a gene called SRY on the Y chromosome kicks in and jump-starts the development of male reproductive organs and the disappearance of female ones. Nipples start to form before SRY activates, so all humans end up with nipples, regardless of their sex. Although usually not capable of lactation, male nipples often still respond to sexual stimulation, so some may disagree with the idea that they're totally "useless." 

2. Wisdom teeth

Humans' third molars, better known as wisdom teeth, can be used to chew food but are often considered unnecessary. In about 22% of people worldwide, at least one out of four wisdom teeth fails to grow in. When they do grow, the teeth are the most likely to become impacted, meaning they don't properly emerge through the gums. That's because humans' jaws are often too small to accommodate the teeth. Some scientists have chalked this up to humans evolving smaller jaws over time, but now, there's evidence to suggest that our childhood diets are more to blame. Consuming hard-to-chew foods, like raw vegetables and nuts, may stimulate jaw growth, while eating soft, processed foods somewhat stunts jaw growth, leaving little room for wisdom teeth, Discover reported.

Related: Why do wisdom teeth come in so late? 

3. The vomeronasal organ

In some humans — scientists aren't sure how many — remnants of a tube-shaped, pheromone-detecting organ can be found poking through the roof of the nasal cavity. This structure, called the vomeronasal organ or Jacobson's organ, is present and functional in many animals, including reptiles, amphibians and mammals. There's anatomical and genetic evidence to suggest that the organ is nonfunctional in the humans who carry it, but this matter is "still widely debated," per a 2018 review in the journal Cureus. 

4. Palmaris longus muscle

The palmaris longus muscle extends from the bottom of the upper arm bone, or humerus, to thick connective tissue, or fascia, in the palm of the hand. Functionally, it's one of the muscles involved in flexing the hand at the wrist and in tensing the palm — but not all humans carry the muscle, and those without it can still execute these motions without issue. Some scientists theorize that the muscle is stronger and more functionally relevant in tree-climbing primates than in land-bound primates, like humans, according to a 2014 report in the journal Medical Hypotheses. 

5. Pyramidalis muscles

The two pyramidalis muscles originate at the joint between the two pubic bones — the pubic symphysis — and extend to each side of the linea alba, a line of connective tissue that runs down the center of the abdomen. These muscles vary in size, and a percentage of humans are missing one or both of the muscles and suffer no ill effects from their absence, according to a 2017 report in the Journal of Clinical and Diagnostic Research. Estimates suggest that between 10% and 20% of people are missing at least one pyramidalis muscle, but these estimates vary depending on the population of people studied.

6. Darwin's point

Darwin's point, or Darwin's tubercle, is a bump that sometimes appears on the rim of the outer ear. Considered a harmless malformation of the ear, the structure is thought to be a remnant of a joint that once allowed the top of the ear to fold down over the ear canal, New Scientist reported. 

7. Auricular muscles

The auricle, or pinna, is the visible portion of the ear on the outside of the head; the muscles attached to the auricle are considered vestigial in humans, meaning they've lost all or most of their original function over evolutionary time. ("Vestigial" is widely thought to mean "completely nonfunctional," but this is a misconception.) While many animals can pivot their ears in response to sounds, humans have lost this ability and some can't even wiggle their ears, according to The New York Times. 

8. The "tailbone"

The human tailbone, or coccyx, is also considered vestigial, meaning it's lost its original function over evolutionary time. Once part of an actual tail, the human tailbone now consists of three to five rudimentary vertebrae fused together to form a single bone; it serves as an anchoring point for many muscles, ligaments and tendons, New Scientist reported. So while it's far from useless, it's no longer a tail.

9. The appendix? (Maybe not.)

Charles Darwin first proposed that the appendix, a pouch-like structure that extends off the large intestine, might be a vestigial organ that once helped our herbivorous ancestors digest hearty plants. The fact that some people are born without an appendix and many have the organ surgically removed without any obvious consequence seemed to support this idea. But more recently, research has revealed possible functions of the appendix in a wide range of mammals, including humans. The organ may be a reservoir for helpful gut bacteria, for example, and also a site where disease-fighting immune cells are born. So is it useless? Maybe not, but get it removed if you have appendicitis. 

10. "Third eyelid"

Birds, reptiles and some mammals, including cats, have a third eyelid that blinks across the eye, from the lower inner corner to the upper outer corner. This windshield wiper-like structure, called the nictitating membrane, doesn't exist in humans, but humans do carry a remnant of the third eyelid in the inner corner of each eye, according to Scientific American. 

This remnant, called the plica semilunaris, looks like a small, fleshy bump. Although sometimes thought to be useless because it doesn't function as an eyelid, it actually supports the rotation of the eyeball and helps with tear drainage. That said, the tissue may be removed in patients who require surgery for narrowing or blockage of the tear duct.

A newfound "protective shield" in the brain helps clear waste from the organ and serves as a sentry tower for watchful immune cells that monitor for signs of infection, scientists reported in a study of mouse and human brains.

The study, published Thursday (Jan. 5) in the journal Science, describes a thin sheet of tissue that measures only a few cells thick and splits an overarching compartment in the brain called the subarachnoid space into two halves horizontally. Several distinct layers of tissue sit between the inner surface of the skull and the outer surface of the brain, and the subarachnoid space lies between two of those tissue layers. The space itself isn't empty; it contains a spiderweb-like network of connective tissue that stretches between the neighboring tissue layers, major blood vessels, and a colorless fluid called cerebrospinal fluid (CSF), according to the online medical resource StatPearls.

The CSF surrounding the brain acts as a shock absorber, similar to the cushioning inside a bike helmet. However, this fluid doesn't hang out only in the subarachnoid space. Instead, it flows through various tubes and compartments in and around the brain, delivering nutrients to the organ while flushing its waste products out into the bloodstream. The newly discovered "shield" likely helps control these important functions of CSF, the study authors concluded.

"The discovery of a new anatomic structure that segregates and helps control the flow of cerebrospinal fluid in and around the brain now provides us much greater appreciation of the sophisticated role that CSF plays not only in transporting and removing waste from the brain, but also in supporting its immune defenses," senior author Dr. Maiken Nedergaard, co-director of the Center for Translational Neuromedicine at University of Rochester and the University of Copenhagen, said in a statement.

Related: How many organs are in the human body? 

The shield, which the authors call the subarachnoid lymphatic-like membrane (SLYM), divides the subarachnoid space into an upper compartment, closer to the skull, and a lower compartment, closer to the brain. Experiments in mice suggested that the thin membrane blocks most proteins from crossing from one compartment into the other, although it allows very small molecules to pass through. (The team also found evidence of the SLYM in tissue samples from adult human brains.)

The newfound membrane may help separate fresh CSF from contaminated CSF containing waste and potentially harmful proteins, such as the amyloid plaques associated with Alzheimer's disease, and help direct these substances out of the brain, the authors theorized. Understanding how this works in a healthy brain and what happens if the shield incurs damage "will require more detailed studies," they noted. 

The study also revealed that a large number and variety of immune cells can be embedded in the shield, and showed that these immune cells increase in number in response to inflammation and advanced aging in mice. This finding hints that the SLYM serves as a site of "immunological surveillance," from which immune cells monitor the CSF for signs of infection and inflammation and can summon additional defenses as needed, the authors concluded. 

However, if the SLYM ruptures, immune cells from the skull's bone marrow can then flood the surface of the brain, an area they normally wouldn't reach. This finding could help explain why traumatic brain injuries often trigger prolonged inflammation of the brain and disrupt the normal flow of CSF through and around the organ, the authors suggested, although these hypotheses will have to be tested. 

Traumatic brain injuries are also linked to an increased risk of developing Alzheimer's down the line, the authors added, and this increased risk may be partially explained by the trauma introducing new cracks in the brain's protective shield — the SLYM, the authors theorize.

The thyroid gland is a small, butterfly-shaped organ in the throat that is very important to health and wellbeing. The thyroid is part of the endocrine system, which is essentially a collection of glands. These glands produce hormones that regulate mood and other various functions in the body — and the thyroid gland is no different. 

"Thyroid hormones impact a host of vital body functions, including heart rate, skin maintenance, growth, temperature regulation, fertility and digestion,” said the late Dr. Jerome M. Hershman, former emeritus professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles.

But how big is the thyroid gland? What is its exact function? And what thyroid conditions should you know about? Keep reading to discover everything there is to know about this organ. 

Thyroid gland: Size

The thyroid gland is 2 inches (5 centimeters) wide and weighs between 20 and 60 grams (0.7 to 2.1 ounces), according to the U.S. National Library of Medicine. 

The gland stretches across the front of the neck, below the voice box. Like a butterfly, it has two wings called lobes that stretch around the windpipe. The wings are connected by a small piece called the isthmus.

Thyroid gland: Function

The thyroid gland controls just about every cell in the human body. It secretes hormones calcitonin, T4 (thyroxine or tetraiodothyronine) and T3 (triiodothyronine) into the bloodstream. The hormones control the rate at which cells and organs turn nutrients into energy and the amount of oxygen cells use. 

"In this way, the thyroid gland is the body's master metabolic control center," said Cindy Samet, a chemistry professor at Dickinson College in Carlisle, Pennsylvania. "Brain, heart and kidney function, as well as body temperature, growth and muscle strength — and much more — are at the mercy of thyroid function."

The thyroid also regulates the brain and nerve function and development, plus the function of the skin, hair, eyes, heart and intestines.

The thyroid works in conjunction with the pituitary gland. The pituitary gland regulates how many hormones the thyroid releases. 

The thyroid gland produces a large amount of T4, but that hormone is not very active. T4 is converted to T3 via an enzyme that removes one of its iodine atoms. 

"Although T3 is much more potent than T4, there is much evidence to support that people with hypothyroidism feel much better when they receive a combination treatment that includes a small amount of T3 with the commonly prescribed T4," Samet told Live Science.

Thyroid gland: Diseases and conditions

Thyroid conditions affect an estimated 20 million Americans and as many as 60% of people with a thyroid disease don't know they have a problem, according to the American Thyroid Association. 

"Women are particularly at risk for a thyroid issue," Hershman said. "One in eight women will develop a thyroid disorder during the course of their lives — that's five to eight times the rate in men."

Graves' disease

One of these conditions is called Graves’ disease, which was discovered by the Irish doctor Robert James Graves in 1835. Graves' disease is an autoimmune disorder. 

The immune system attacks the thyroid gland and makes it become overactive. An overactive thyroid is a condition called hyperthyroidism. A bulge on the neck, called a goiter, is a common symptom. The patient may also experience an increased heart rate, according to the National Library of Medicine (NLM).

Hypothyroidism 

Hypothyroidism, also known as underactive thyroid, is the opposite of Graves' disease. It occurs when the thyroid gland does not produce enough hormones. This can cause body functions to slow down or stop completely.  

Thyroid cancer

Cancer is another disease that can affect the thyroid. A 2017 study published in the Journal of the American Medical Association (JAMA) has found that between 1975 and 2013 the number of thyroid cancer cases diagnosed each year has more than tripled. Cases of advanced forms of the disease rose by about 3% each year while deaths rose by about 1% each year. 

A lump or swelling on your thyroid gland is called a nodule. Nodules can be harmless, but some can cause a production of too much hormone or be cancerous, according to the Endocrine Society.  

"Up to 70 percent of middle-age females and 40 to 50 percent of middle-age males have thyroid nodules, said Dr. Melanie Goldfarb, an endocrine surgeon and director of the Endocrine Tumor Program at Providence Saint John's Health Center in Santa Monica, California, and an assistant professor of surgery at the John Wayne Cancer Institute in Santa Monica. "You can also be born with an extra piece anywhere as high up as the base of your tongue,” Goldfarb adds. 

In some medical cases, such as cancer, the thyroid is removed. Humans can live without their thyroid if a hormone pill is taken daily.

Promoting good thyroid health

Science tells us that for the thyroid to remain healthy, it needs iodine to produce hormones, but just a little. 

"It turns out that one teaspoonful of iodine is enough for a lifetime of thyroid hormone production. But the thyroid gland needs a constant supply of iodine, so we must intake iodine in some form on a daily basis and not all at once," Samet said. Too much iodine can actually make the thyroid produce less hormones. 

The best way to get iodine is through eating healthy foods, such as seafood and dairy products. You can also get it by seasoning your food with iodized salt.

Additional resources

• Johns Hopkins: Thyroid Gland
• Digital Journal: Thyroid Gland Disorders Treatment Market- Asia Pacific Increases Thyroid Gland Disorders Treatment Demand, North America Continues to Lead It
• FDA: FDA Alerts Veterinarians and Pet Food Manufacturers about Potential Presence of Thyroid Hormones in Pet Foods and Treats
• NLM: Metastatic Tumors of the Thyroid Gland

With the best Philips electric toothbrush deals, you can save as much as $150 dollars on some of the brand’s premium products. Philips makes a great range of electric toothbrushes, from more basic models like the Sonicare One, to the top of the range Sonicare 9900 Prestige, which gives you in-depth analytics and feedback on your brushing habits to help you improve your dental health. 

The brand operates with sonic technology, with brush heads moving up to 62,000 movements per minute. According to Philips, this provides the equivalent of a whole month;s worth of manual brushing in just two minutes. 

Switching from a manual to one of the best electric toothbrushes is undoubtedly a great way to step up your oral care routine — but these devices can come at a price. That’s why it’s great to take advantage of discounts from the likes of Target, Walmart, Best Buy and Amazon to save you money on a top model.

If you don't think Philips is your brand, you can check out the competition with our selection of Oral-B electric toothbrush deals.  

• View the latest deals on Philips toothbrushes at Target
• Walmart has got great discounts on Philips toothbrushes
• Check out these Philips electric toothbrush deals at Best Buy

Cyber Monday Philips electric toothbrush deals

Which Philips electric toothbrush is best for you?

We’ll be honest, Philips has got an awesome range of electric toothbrushes and that can make finding the best one for you a little overwhelming. But the range is so extensive that there’s bound to be one to suit your budget and needs.

If this is your first time switching from a manual toothbrush to a power device, check out our guide on how to use an electric toothbrush.

Using an electric toothbrush is a great way to improve your oral hygiene, especially as 31 percent of Americans are failing to brush their teeth at least twice a day, with 2 percent admitting to not brushing at all, according to a study by Delta Dental.

Whether you want a battery-powered or rechargeable toothbrush, need one with a tongue cleaner, interval timer, travel case or even sensors to tell you how well you’re brushing, our round up of Philips electric toothbrushes makes it easy to invest in your dental health today.

Philips electric toothbrushes on sale

Philips Sonicare ProtectiveClean 5100 deals

If you suffer with sensitive teeth, or are prioritizing your gum health - particularly receding gums - then this is the Philips electric toothbrush that has been missing from your life! Designed to give your teeth a thorough but gentle clean without damaging gums or causing pain to sensitive teeth, it’s a bestseller for good reason.

It comes with three modes: Clean, White and Gum Care, which allows for an extra 60 seconds of reduced-power brushing to gently clean and massage your gums. If you brush too hard, which can cause gum damage, the toothbrush will vibrate. It also buzzes when it’s time to move to a new area of the mouth, providing an efficient clean that leaves your mouth feeling ‘dentist-fresh’.

Reviewers rave about this electric toothbrush, giving it a generous 4.7 out of 5 stars overall, and praising it for its helpful alerts and thorough cleaning (although some claimed there was little difference between the cleaning modes, other than the length of time they lasted).

Philips recommend you buy specific brushes for White or Clean mode, which some users said was an unnecessary expense, as the brush heads for different modes aren’t included in the price. Other reviewers said it was a shame that the travel case didn’t have a charger, or charge the brush itself.

Philips Sonicare DailyClean 1100 deals

If you have a tight budget, you can still find a decent budget Philips electric toothbrush to keep teeth sparkling clean without breaking the bank. Granted, the Sonicare DailyClean 1100 is fairly basic and doesn’t have the bells and whistles of the more expensive models. It doesn’t have an app, pressure sensors or a travel case, and it only has a single cleaning mode, but if you’re not after loads of features then it’s really excellent value.

And as you’d expect from Philips, even though it’s inexpensive, it still has a powerful standard of teeth cleaning as well as a timer and ‘quadpacer’ that beeps to prompt you to move to the next area of your mouth while brushing. It’s super easy to use so it’s a great choice for anyone using an electric toothbrush for the first time.

Reviewers are big fans of this model, giving it 4.7 stars. While some say it’s not as powerful as the more expensive Philips electric toothbrushes, most were satisfied with its performance and didn’t feel they need the extra features of the more costly models. One reviewer said: “This model is perfect value and the more expensive models ($25+) only have small additional features.” 

Negative reviews however said the battery life wasn’t as long as the promised 14 days, and the toothbrush is lacking a light to indicate battery life.

Philips Sonicare DiamondClean 9750 deals 

If you’re looking for an electric toothbrush that looks as good as it performs, then add the DiamondClean 9750 to your shopping cart right now! Sleek, with gold details and a stylish glass charger, it’s miles away from the traditional image of an old toothbrush in a chipped mug. But don’t judge a book by its cover as it’s got way more than just good looks. This electric toothbrush claims to remove 10 times more plaque and improve gum health by up to seven times in two weeks if you switch to Gum Health Mode (it also promises to remove up to 100 percent more stains in just three days compared with a manual toothbrush, using the Whiteplus Mode).

But what we really love about this toothbrush is the smart tech. We’re not joking when we say this is one of the best electric toothbrushes on the market. Sync it with the Sonicare app and it knows which of the four brush heads you’re using, so it can set the correct brushing mode. It’ll give you real-time feedback as you brush, mapping a 3D image of your mouth so it can tell you when to move to a new area for brushing - providing a completely efficient clean in ways you’ve never experienced before.

Press too hard on your teeth or miss a spot and you’ll get an alert, and it’ll even give you a ‘progress report’ on your brushing performance that you can then share with your dentist or hygienist. Traveling? This slimline toothbrush comes with a USB travel case which charges it in between brushes.

Users can’t stop raving about this product, rating it a healthy 4.7 out of 5 stars on Amazon. One reviewer said they’d reduced their visits to the hygenist by 50 percent after investing in a Sonicare DiamondClean 9750 as they no longer needed to have their teeth professionally cleaned so often, while others loved it for giving their teeth that ‘dentist-fresh’ feeling.

Negative feedback said the app was glitchy and reported difficulty connecting it to the brush. Some reviewers also complained about pop-up ads on the app, and expressed concerns about privacy and data collection when using it.

Philips Sonicare 9900 Prestige deals

We’ll be honest, we’re a little bit in love with this rose gold Philips electric toothbrush and stylish leatherette travel case with USB charging. But it’s not just good looking - this is a seriously powerful bit of kit that comes with SenseIQ technology, a combination of smart features that use built–in sensors to observe your brushing style and adapt the pressure accordingly. If you’re ready to invest in your dental health, and a whiter smile, this toothbrush claims to remove 20 times more plaque and up to 100 percent more stains in less than two days compared with a manual toothbrush, thanks to its angled bristles and triangular tips to get to those hard to reach areas. It also comes with a two-year warranty.

If you’re someone who is prone to brushing too hard, you will get an alert in the form of a light and vibration, then if you don’t reduce the pressure, this toothbrush will adapt the intensity. Just like the DiamondClean, the Sonicare app provides you with useful data, including a 3D map of your mouth and where you need to concentrate on brushing, real-time feedback, recommendations and progress reports that you can share with your dental health specialist.

It gets an impressive 4.5 out of 5 stars on Amazon, with one reviewer saying: “My teeth actually twinkled”. Another user asked: “What magic could a toothbrush offer that makes it worth the cost of a flight to Vegas?” Before answering: “The app, that’s what. It brings the hygienist to your bathroom.”

Negative reviews cited issues with the app being unreliable and concerns over privacy and data, and others said it was over-priced.

Philips Sonicare for kids sonic electric toothbrush deals

If you’re a parent you’ll know that getting the kids to brush their teeth, let alone for the dentist recommended two minutes, can be a military operation. Introducing the Philips Sonicare For Kids - an electric toothbrush that promises to make teeth cleaning fun.

With a color choice of pink or blue, the toothbrush comes with a child-friendly handle, stickers to customize it and two cleaning modes with different intensities. It also pairs with an interactive app with animations and special rewards for brushing properly, which parents say is an incentive for children to brush their teeth for longer. The app also follows the kids as they clean their teeth, prompting them to brush more thoroughly and move the toothbrush around the whole mouth for an efficient clean.

Reviewers praised the Sonicare for kids sonic electric toothbrush for the awesome way it encouraged their children to brush better and for longer. "My son N E V E R brushed his teeth willingly prior to this brush/app. Now I have him begging to brush his teeth before school," claimed one delighted parent.

Some reviewers said the app didn’t work with every smartphone, and the brush head was a bit too big for younger children (which meant an extra cost buying a smaller one). Parents also warned that younger kids would need proper supervision using it to prevent gum damage (it’s not suitable for under-threes).

With these excellent Oral-B electric toothbrush deals, you can pick up a top of the range toothbrush from a premium brand, without having to pay big prices.

If you want a basic, effective electric toothbrush, or something high-tech with analytics up to your elbows, Oral-B electric toothbrushes come at a range of prices with a variety of capabilities — so you're sure to find something that's right for you. At the top of the range is the iO Series 9, which includes smart features such as a pressure sensor, AI-powered app and a travel charging case. A more basic model is the Oral-B Pro 1000, which gives the powerful clean of an Oral-B toothbrush at more than half the price of the brand’s other options. 

But if you see an Oral-B electric toothbrush deal you like, be prepared to act quickly. Electric toothbrushes tend to go out of stock quickly, so don’t miss the chance to save on one of these top models. 

• Shop Oral B electric toothbrush deals at Amazon
• Check out Walmart's Oral B toothbrushes
• Save over $50 on Oral-B toothbrush deals at Target

Oral-B electric toothbrush deals

Which Oral B toothbrush deal is best?

Ready for an awesome Oral B toothbrush deal? There’s a ton of products to choose from, from the futuristic Oral-B Genius X, that uses Artificial Intelligence to track and improve your brushing habits, to the Oral B Pro Crossaction 1000, which has a clever pressure sensor designed to vibrate if you brush your teeth with too much force - preventing gum damage.

Whether you want a basic toothbrush with a timer or are looking for a more feature-rich one with an integrated ‘oral hygiene coach’ (yes, really!), Oral B has every need and budget covered. And if you’re someone who has to have the newest model of everything, then you’ll love the Oral B iO Series 9. This electric toothbrush syncs with an app to reveal real-time brushing performance, so you know that every time you clean your teeth you’re hitting the spot. It’s like having your own personal dentist in your pocket!

Oral B electric toothbrushes on sale

Oral B Genius X  Electric Toothbrush deals 

True to its namesake, the Oral B Genius X is a genius at getting teeth whiter and cleaner. This smart toothbrush with AI tech connects with an app for real time feedback on how to brush your teeth better.

The 360 SmartRing has different colored LED lights so you can customize your toothbrush - gaining information on timings and pressure as you brush your teeth. With six modes, including Whitening and Sensitive, and a charge that lasts up to two weeks, it also comes with a neat travel case making it a great choice for people on-the-go.

Oral B Pro 3000 deals 

Want whiter teeth? The Oral B Pro 3000 is not only budget-friendly, its CrossAction brush head helps to remove stains from first use, and its pressure sensors protect gums. Connect your brush via Bluetooth to your smartphone and the Oral B app, so you can track how well you are cleaning your teeth. The brush has three different modes - daily, gum care and sensitive - which works well to whiten teeth without causing discomfort.

Oral-B iO Series 9 Electric Toothbrush deals

As the newest model from Oral B, the iO Series comes with a smart element that means it glows red if you brush too hard. The in-built AI tracks brushing style, allowing you to make sure you achieve total coverage, so no tooth goes unbrushed. The round brush head and its multi-way oscillating and rotating angles help you target those hard-to-reach areas and remove plaque along the gum line.

Team it with the Oral B app via Bluetooth for insight into your oral hygiene routine including 3D graphics and data about your cleaning style. This Oral B electric toothbrush comes with a magnetic charger that tops up the battery in just three hours. The only issue is that replacement heads are expensive, and you could save money by choosing a more basic toothbrush.

Oral B Pro Vitality Sensitive Clean deals 

The Oral B Pro Sensitive Clean is an affordable model, with just one mode that starts as soon as you press the ON button. The inbuilt two-minute timer, which flashes and beeps when you’ve reached the optimum time, helps to encourage better brushing habits. The toothbrush comes with a FlexiSoft brush head, which those with sensitive teeth will appreciate, as it brushes teeth and gums in a gentle rotating motion without too much pressure. 

It also comes with interdental tips - ideal for getting into those hard to reach places. Unfortunately, you can’t use this Oral B toothbrush with the app, and the battery life isn’t as good as the Oral B iO Series 9, either.

Oral B Smart 1500 deals 

This slick electric toothbrush rotates, pulsates and oscillates for a superior 3D clean. Gum pressure sensors warn if you’re brushing too hard, and it’s easy to use with just one mode. It comes with a two-minute timer for optimum cleaning and while a full charge takes 12 hours, it’ll last you up to two weeks.

Oral B toothbrush head deals

Ready to replace your toothbrush heads? Or maybe you just want to stock up while there are great deals to be had. Either way, now is the time to grab some replacement Oral B electric toothbrush heads at the lowest prices.

Save yourself a bundle on dental care this Cyber Monday offer — get 40% off the Waterpik Cordless Advanced Water Flosser. When a brand name is synonymous with a kind of product, you know they make the best on the market. Waterpik water flossers are no exception. 

Our testers tried out the Waterpik cordless select and the Waterpik Ultra, both of which made it into our guide to the best water flossers, having impressed our team no end. While we've not yet had the pleasure of trying out the Cordless Advanced, 70% of users on Amazon rated it the full five stars, with a 4.4 out of 5 star rating overall.

Cordless water flossers are a handy and portable alternative to corded water flossers, which tend to have larger reservoirs but are restricted by their need for a power outlet. The Waterpik cordless water flosser is global voltage compatible and comes with a micro-fiber travel bag, tip storage case, and water plug for use on the go.

The Waterpik Cordless Advanced water flosser removes up to 99.9% of plaque and is up to 50% more effective than dental floss for improving gum health. Just fill the reservoir with warm water, place the tip in your mouth, and start flossing.

With an electronic pressure control and three settings, the Cordless Advanced lets you personalize your water pressure intensity, plus it's waterproof and can be used in the shower. Using a unique combination of water pulsation and pressure it works to remove plaque and debris that can cause bad breath, gum disease and tooth decay.

If you're still not sure whether to make the jump, a study in Compendium compared a group of people who only brushed their teeth with another group who brushed their teeth and used a water flosser. Not flossing at all carries a higher risk of oral hygiene problems, including gum inflammation and disease. The group who added water flossing to their dental hygiene routine had significantly improved gum health after just four weeks. This water flosser is also approved American Dental Association (ADA), earning their Seal of Acceptance, so you know you can trust it with your dental hygiene. 

More Cyber Monday water flosser deals

A 60% reduction on one of our favorite electric toothbrushes, hum by Colgate, sees it coming down from the heights of $69.99 to $27.99 — a much more affordable option. This Cyber Monday deal is sure to be gone soon, so cash in while you still can and get a premium toothbrush for more than half the price.

This app-driven smart toothbrush made it into our guide to the best electric toothbrushes, having impressed our tester who tried it out earlier this year. Our tester found that the light and compact design made it easy to maneuver, allowing them to access every nook and cranny without jabbing at the gums like other brushes with larger heads. It also doesn’t take up too much space on your bathroom shelf, which is always a bonus. Bluetooth connectivity allows you to record your brushing and track which areas you need to clean further in the app. 

The hum by Colgate comes with three modes of powerful sonic vibration, allowing you to personalize your brushing experience by choosing the vibration level that suits you; choose from normal, sensitive, or deep clean. This particular kit comes with one electric adult toothbrush, one charger, one carrying case and one refill brush head, giving you even more for your money this Cyber Monday. 

• Amazon: Oral-B electric toothbrush deals 
• Walmart : discounts up to 50% on Oral-B toothbrushes
• Target: Black Friday electric toothbrush deals

We found the hum to be one of the more functional electric toothbrushes we've tested. The single button lets you shift through three different vibration modes (or two if you buy the battery-powered version): Normal, Sensitive, and Deep Clean. While it might be confusing to know which mode other brushes with multiple brushing modes are set to, the hum makes it very clear through LED lights. 

Charging is also easy. The rechargeable hum comes with a charging base that starts charging your toothbrush when you set it down. The battery-powered toothbrush takes two AAA batteries. 

Other features of the hum include a built-in two minute timer and a Bluetooth connected app. The app has a lot of features, which could make it confusing for some. But once you get the hang of it, the app can guide you to brush better. As you brush, you can also earn Smile Points from Colgate, which give you $1 per 100 points to spend on things like replacement brush heads. 

If purple isn't your color, you can also get the hum in slate grey for 42% off, or in blue for 49% off.

More Cyber Monday electric toothbrush deals

Haven't found what you were looking for? Check out our tried and tested round-up of the best electric toothbrushes you can buy right now.

Tired, fraying toothbrushes — be gone. This Cyber Monday you can invest in your dental hygiene with 50% off the highly-rated Oral-B Genius X Limited at Amazon, which tops our guide to the best electric toothbrushes. 

The Oral-B Genius X Limited usually retails for $199.99, but during this year’s Cyber Monday sales you can pick up one of the market-leading toothbrushes for $99.99.

The Oral B Genius X is a powerful, Bluetooth-enabled electric toothbrush that allows users to get the most out of every brushing session. From its two-week battery life to its six different cleaning modes, and its smart, connected functionality to its interactive app that tracks and monitors brushing habits and patterns. If you've been meaning to upgrade to an electric toothbrush, Cyber Monday could be the time to do so — although you'll have to hurry to make the $100 saving. 

• Amazon: Oral-B electric toothbrush deals 
• Walmart: discounts up to 50% on Oral-B toothbrushes
• Target: Cyber Monday electric toothbrush deals

When our tested tried out the Oral-B Genius X Limited earlier this year, we found this brush was able to take our teeth-brushing-game to new heights. It was fascinating to track our dental habits and patterns in order to adjust our routine if needed. And it's because of these reasons (and more) that we awarded the Oral-B Genius X Limited the coveted top spot in our best electric toothbrushes guide.

Upon testing, we scored the Oral B Genius X limited a brilliant 4.5 stars out of five and found it ideal for anyone wanting to improve and maintain good dental hygiene. 

Why? For starters, unlike your average manual toothbrush, it uses A.I. technology through its interactive app to track and monitor your brushing habits and patterns. Once the app has collected this data, it can supply users with a set of oral hygiene goals with coaching tips and tricks. 

But even if you don’t use the app, there are still plenty of features to love. It has six cleaning modes that provide you with a tongue cleaning option, a sensitive mode, whitening features, gum care, and pro cleaning alongside your day-in-day-out daily clean option, thanks to its powerful oscillating-rotating brush head.

Battery-wise, from the moment you unbox the Oral B Genius X you can start using it as it comes with some charge already. However, after using your toothbrush and depleting its battery, this clever electric number should take around 14 hours to charge. This may sound long, but it’s actually a lot less than many electric toothbrushes, which take up to 18 hours. 

Unsure on whether this electric toothbrush is for you? If you're looking for another fabulous Cyber Monday deal on electric toothbrushes, you can save up to 60% on the top-rated hum by Colgate. But remember: these deals won't be around forever. 

Discover more of the best Cyber Monday deals across fitness and health at Live Science.

Take a look at the Cyber Monday electric toothbrush deals here, and you'll definitely consider upgrading your current device or swapping one for your manual brush. After all, there are some fantastic Cyber Monday discounts on offer at the moment — but be quick because some deals have limited stock, and there are only a handful left in some cases!

Even so, you're spoiled for choice. The Colgate Hum, for example, is an excellent package with a toothbrush, charger, refill head, and carrying case, and it's yours for 64% less right now at Amazon. If you can pay a little more, you can grab the Oral-B Genius X with its 50% discount, making it just $99 at Amazon.

Alongside these great discounts, there are models by Philips to take into account, again with eye-catching deals. But why switch to the best electric toothbrushes? In short, dentists recommend you change from a manual brush because electric models are better at removing plaque. According to a major Cochrane review, they can remove 20% more plaque and reduce your risk of developing gingivitis by 11%.

Electric toothbrushes often have timers and pressure sensors, too, so you can be sure you're brushing for the right amount of time and not damaging your teeth by pressing hard. In some cases, the toothbrushes will even let you know if you have a decent brushing technique.

Of course, they're not cheaper than a manual brush, but you wouldn't expect them to be. They also need recharging, though less often than you may think. So let's look at the Cyber Monday electric toothbrush deals, including Oral-B electric toothbrush deals and Philips electric toothbrush deals. You'll be smiling in no time.

• Amazon: Oral-B electric toothbrush deals 
• Walmart : discounts up to 50% on Oral-B toothbrushes
• Target: Cyber Monday electric toothbrush deals

Haven't found what you were looking for? Check out our tried and tested round-up of the best electric toothbrushes you can buy right now.