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All dog owners know exactly what we mean by "puppy-dog eyes." It's that heart-melting expression when your pooch looks up at you with big eyes seemingly full of naive innocence. And it's no coincidence that people can't resist this adorable facial expression – in fact, it seems that dogs evolved the ability to make puppy-dog eyes specifically to endear themselves to humans.
Researchers at Pittsburgh's Duquesne University have discovered that dogs have an additional facial muscle that helps them make their eyes appear larger. This muscle is totally undeveloped in wolves – which dogs diverged from some 30,000 years ago. And compared to wolves, dogs have a much higher proportion of fast-twitch muscle fibers. This allows them to quickly make a wide variety of facial expressions, improving their communication with people. These findings suggests that dogs evolved anatomically in order to better connect with humans, most likely as a result of domestication.
Oh, those puppy-dog eyes:
- Through millennia of selective breeding, humans played a significant role in the development of dogs' animated, expressive faces.
- Our ancestors seem to have preferred dogs that could bark, rather than howl like wolves, and selectively bred for this trait. Barking, which would have been more useful than howling as a type of alarm, uses fast-twitch muscle fibers, whereas howling uses slow-twitch fibers.
- Interestingly, this phenomenon appears to be unique to dogs. Scientists have not observed a corresponding change in the facial muscles of domesticated cats when compared to their wild cousins.