Dogs and humans have been living side-by-side for about 15,000 years, so you might think we know each other pretty well. But there's more to dogs than fetching and playing dead. Here are some little-known facts about man's best friend.
Dogs get our diseases ...
Humans and canines aren't so different after all, at least regarding what makes us sick. About 6 million dogs are <a href="http://www.livescience.com/animals/090813-animal-cancer.html">diagnosed with cancer</a> each year, and dogs get canine versions of rare human disorders like the <a href="http://www.livescience.com/health/pit-bull-terriers-genetic-disorders-canine-disease.html">brain-wasting neuronal ceroid lipofuscinosis</a>
that leads to the inability to walk or control their muscles. While
illness is sad for humans and pets alike, sharing diseases benefits both
species. Clinical trials are easier to run on pets, giving doctors an
animal model of human disease -- and Fido a chance for a cure.
... And they can smell our diseases, too
If you have cancer, diabetes, or epilepsy, your dog might be the first to know. Studies have shown that <a href="http://www.livescience.com/health/dogs-sniff-prostate-cancer-100617.html">dogs can be trained to sniff out cancers</a>
of the lung, breast, skin, bladder and prostate. Researchers suspect
the canines are picking up on extraordinarily faint scents given off by
the abnormal cells.
Dogs are also being increasingly used as service animals for people
with diabetes, whose health can be harmed when their blood sugar peaks
or drops. Specially trained dogs can detect the scent of these
fluctuations (sweet for high blood sugar, acidic for low) and alert
their owners before they even feel symptoms.
Most mysterious of all are scattered reports that dogs can predict an
epileptic seizure 45 minutes before it begins. No one knows what the
dogs might be picking up on, but theories range from an unknown smell to
subtle behavioral changes.
See Spot think
Dogs can be as <a href="http://www.livescience.com/animals/090808-smart-dogs.html">smart as 2-year-old children</a>,
according to research presented in 2009 at a meeting of the American
Psychological Association. Border collies are the top dogs in the
intelligence category, with some in the breed capable of understanding
up to 200 words. Poodles, German shepherds, Golden retrievers and
Dobermans round out the top five smartest breeds. (The most popular
breed in America, the Labrador retriever, comes in at number seven.)
Older breeds like hound dogs, bulldogs and beagles are among the slow
learners of the doggie world, the researchers reported. Unlike newer
dog breeds, which are designed for companionship and sociability, old
breeds were bred to sniff and hunt, perhaps giving them more brawn than
Your furball can make you sick
We've all heard the canard that dogs' mouths are cleaner than humans (<a href="http://www.lifeslittlemysteries.com/is-a-dogs-mouth-cleaner-than-a-humans-0500/">they're not</a>),
but in reality, dogs can carry pathogens that harm humans. Rabies, a
fatal neurological disease, is the most famous (remember Old Yeller?),
though vaccines, mandated by law in most states, can stop the spread. In
a few cases, dog food has been known to cause food poisoning in humans,
thanks to contamination by <a href="http://www.livescience.com/health/pet-food-salmonella-outbreaks-100809.html"><em>Salmonella</em> bacteria</a>.
Perhaps creepiest of all is a 2003 study published in The Veterinary
Record, which found that humans could contract the parasitic roundworm <em>Toxocara canis</em>
just be stroking an infected dogs' fur. The roundworm, which grows in
dogs' intestines, can grow in the back of the eye in humans, causing
blindness. They also sometimes take up residence in human livers and
Roundworm infections in humans are rare, and proper veterinary care
can ensure that dogs stay worm-free. Still, British veterinarian and
study co-author told New Scientist magazine in 2003, hygiene is
important for dog owners. "Wash your hands before meals," he told the
magazine, "and after a good cuddle."
Dogs feel envy ...
Dogs know when they're not getting a fair shake. A 2008 study
published in the journal Proceedings of the National Academy of Sciences
found that when dogs saw other dogs getting treats for a trick they'd
been performing unrewarded, the unrewarded dogs became agitated,
scratching themselves and avoiding the gaze of the rewarded dogs. They
also <a href="http://www.livescience.com/animals/081208-dog-envy.html">stopped doing the trick much faster</a> than if they were alone and not getting a reward.
The dogs' version of jealousy wasn't as sophisticated as a human's:
The animals didn't seem to mind if other dogs got sausage while they
just got bread, and they didn't care if another dog got food for nothing
while they had to do tricks for a snack. But, the researchers wrote,
the findings were good evidence that being green with envy isn't just a
... But not guilt
Those puppy-dog eyes Fido gives you when you scold him over knocking
over the garbage can for the umpteenth time aren’t a sign of guilt,
researchers say. He's just <a href="http://www.livescience.com/animals/090611-guilty-dogs.html">responding to your rebuke</a>.
When dog owners thought their dogs had eaten a forbidden treat and
reprimanded them, the pooches looked just as "guilty" regardless of
whether or not they had actually eaten the treat. In fact, dogs who were
wrongly accused of snack-snatching often looked more guilty than dogs
who had really eaten the treat. Turns out those soulful eyes don't
reflect any soul-searching, after all.</p>
Docile dogs live longer
On the other hand, if your dog stays out of the garbage, it may be in
for a longer life. Obedient, docile dog breeds live longer, according
to research published in June 2010 in The American Naturalist. The study
compared the energy use, personalities, growth rates and life spans of
56 <a href="http://www.livescience.com/animals/most-popular-dog-breeds-100803-1.html">dog breeds</a>.
After controlling for factors like body size, the researchers found
that bold, aggressive breeds lived fast and died young. They grew faster
than obedient, eager-to-please breeds, and also had higher energy
needs. The findings suggest that in selectively breeding for
personality, humans inadvertently tapped into linked traits like
metabolism and longevity.
Dogs are the most diverse-looking mammals around
From the droopy Bassett hound to the sleek-and-slim Weimaraner, dogs
show an amazing diversity in body shape. A study published in The
American Naturalist in 2010 found that the differences between <a href="http://www.livescience.com/animals/dog-skulls-evolution-100125.html">dog breeds' skulls</a>
are as pronounced as the differences between completely separate mammal
species. A Collie skull, for example, is as different from a Pekingese
skull as a cat's skull is from a walrus's.
All of this diversity makes dogs a great species for studying how
genes work, allowing researchers to link genes to certain traits -- like
what makes <a href="http://www.livescience.com/animals/dog-breed-genes-100111.html">Shar-Peis wrinkly</a> and dachshunds so stubby.
Lassie, religious icon or social glue?
In ancient times, people saw dogs as more than useful animals; dogs
also had a spiritual role. The three-headed hound called Cerberus
guarded the underworld in Greek myth, while the ancient Egyptian
embalmers took Anubis, the jackel-headed god, as their patron. In Mayan
folklore, dogs were believed to lead the dead to the afterlife. In
Nepal, the autumn festival of Tihar sets aside a day to honor dogs with
flower garlands and food.
Nowadays, dogs are more likely to be seen as pets than religious figures, but people are still <a href="http://www.livescience.com/animals/071022-pet-obsession.html">crazy about canines</a>.
According to a 2009-2010 survey by the American Pet Products
Manufacturers Association, 39 percent of American households have at
least one dog for a total of over 77 million pet dogs hunkered down in
American homes. In <a href="http://www.livescience.com/animals/babies-steal-dogs-spotlight-100815.html">one recent survey</a>,
80 percent of dog owners reported interacting with their dogs for more
than two hours a day. Many reported viewing their pets as their
Man's best friend may even net you more human friends. A 2000 study
published in journal of The British Psychological Society found that
walking with a dog at least tripled the number of social interactions a
person had. Unfashionable pet owners take heart: The dogs elicited
positive social contact even when the animal looked fierce or the owner
dressed in shabby clothes.