Picturing how our species might appear in the far future often invites wild speculation over stand-out features such as height, brain size, and skin complexion. Yet subtle shifts in our anatomy today demonstrate how unpredictable evolution can be.
Take something as mundane as an extra blood vessel in our arms, which going by current trends could be common place within just a few generations.
Researchers from Flinders University and the University of Adelaide in Australia have noticed an artery that temporarily runs down the center of our forearms while we're still in the womb isn't vanishing as often as it used to.
That means there are more adults than ever running around with what amounts to be an extra channel of vascular tissue flowing under their wrist.
"Since the 18th century, anatomists have been studying the prevalence of this artery in adults, and our study shows it's clearly increasing," says Flinders University anatomist Teghan Lucas.
"The prevalence was around 10 percent in people born in the mid-1880s compared to 30 percent in those born in the late 20th century, so that's a significant increase in a fairly short period of time, when it comes to evolution."
The median artery forms fairly early in development in all humans, transporting blood down the center of our arms to feed our growing hands.
At around 8 weeks, it usually regresses, leaving the task to two other vessels – the radial (which we can feel when we take a person's pulse) and the ulnar arteries.
Anatomists have known for some time that this withering away of the median artery isn't a guarantee. In some cases, it hangs around for another month or so.
Sometimes we're born with it still pumping away, feeding either just the forearm, or in some cases the hand as well.
To compare the prevalence of this persistent blood channel, Lucas and colleagues Maciej Henneberg and Jaliya Kumaratilake from the University of Adelaide examined 80 limbs from cadavers, all donated by Australians of European descent.
The donors raged from 51 to 101 on passing, which means they were nearly all born in the first half of the 20th century.
Noting down how often they found a chunky median artery capable of carrying a good supply of blood, they compared the figures with records dug out of a literature search, taking into account tallies that could over-represent the vessel's appearance.
The fact the artery seems to be three times as common in adults today as it was more than a century ago is a startling find that suggests natural selection is favoring those who hold onto this extra bit of bloody supply.
"This increase could have resulted from mutations of genes involved in median artery development or health problems in mothers during pregnancy, or both actually," says Lucas.
We might imagine having a persistent median artery could give dextrous fingers or strong forearms a dependable boost of blood long after we're born. Yet having one also puts us at a greater risk of carpal tunnel syndrome, an uncomfortable condition that makes us less able to use our hands.
Nailing down the kinds of factors that play a major role in the processes selecting for a persistent median artery will require a lot more sleuthing.
Whatever they might be, it's likely we'll continue to see more of these vessels in coming years.
"If this trend continues, a majority of people will have median artery of the forearm by 2100," says Lucas.
This rapid rise of the median artery in adults isn't unlike the reappearance of a knee bone called the fabella, which is also three times more common today than it was a century ago.
As small as these differences are, tiny microevolutionary changes add up to large-scale variations that come to define a species.
Together they create new pressures themselves, putting us on new paths of health and disease that right now we might find hard to imagine today.
This research was published in the Journal of Anatomy.
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Mike McRae is a part-time Journalist at ScienceAlert. He has been telling science stories in one form or another for more than 20 years, and expertly navigates a broad range of subjects, from health and neuroscience to the weirdness of quantum physics. From classroom teacher to journalist, Mike has contributed to the CSIRO's magazines, The Guardian, the ABC and Australian Financial Review. He is the author of popular science books "Tribal Science: Brains, Beliefs," and "Bad ideas and Unwell: What Makes a Disease a Disease?" Mike is slowly building a collection of cephalopod tattoos on his right arm and swears there's still room for a nautilus or two.
"To compare the prevalence of this persistent blood channel, Lucas and colleagues Maciej Henneberg and Jaliya Kumaratilake from the University of Adelaide examined 80 limbs from cadavers, all donated by Australians of European descent. "Reply
What other studies do you have? This is a very specific sample of a specific population and does not cover other ethnicities or other regions of the world...Please add some more statistically relevant data
I have an issue with this as an evolutionary trend - natural selection as the driving force behind evolution requires that subtle variations in a species create an advantage, that over generations cause that variation to be more successful in reproducing. That is the mechanism. How is this process occuring in the case of this artery? Given that the study is not flawed, there is undoubtedly another non-genetic process involved here - perhaps the authors might consider (for example) dietary changes over the 20th century?Reply
There are some unanswered questions here. For instance, what is the advantage of the extra blood flow to the hands? Evolutionary changes only occur when having something allows you to pass on your genes better than not having it, or vice versa. Unless people with the extra artery are far more successful, or live to adulthood where those without the artery do not, evolution may not be playing a part in this. Since a small sample of mankind was studied, it is likely that some segments of humankind has always had this extra artery, but no one has ever bothered to check for it.Reply
Growing an extra artery is not neccessarily an advanvatage, but merely a change as to our lifestyle. I.e. Many people started typing in the late victorian period and even more so today. This could be the reason why these changes are happening. Also on top of this, I have surmised that every one can actually change their own dna in their life time. What you do in the first 25 years of your life are the most important that you could do to maintain a healthy life and to produce the next generation!Reply
The fact that a semi-dormant artery runs through our forearms clearly indicates that there was once a need for this additional blood flow. Perhaps this artery was initially formed in a time when enhanced dexterity was essential for survival. For modern times the dexterity needed for keyboarding and thumbing cell phone text (or even penmanship - still) has excited the artery's control mechanisms. This could explain the new prominence, but how many 200,000+ year-old cadavers does science have to work with? And the concept of a dire need for enhanced dexterity is also worth some thought.Reply
There is also the possibility that the artery was more functional in the not so distant past, when manual labour - particularly in largely agrarian societies - was more widespread. Manual labour has become less prominent in Western societies with the advent of the Industrial Revolution, and the subsequent development of steam and electrical energy, closely followed by the introduction of internal combustion engines enabled by the vast amount of energy released in hydrocarbon exploitation. This more recent de-emphasis on manual labour isn't uniformly global, so, as other posters have pointed out, a wider sample size might find that other societies have contnued to have a functional mid-forearm artery.