Biology

How dogs quickly evolved a unique facial muscle to better manipulate humans

How dogs quickly evolved a uni...
The raised inner eyebrow movement in dogs is driven by a muscle which doesn't consistently exist in their closest living relative, wolves
The raised inner eyebrow movement in dogs is driven by a muscle which doesn't consistently exist in their closest living relative, wolves
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This evolutionary shift happened quickly as dogs only split off from wolves a little over 30,000 years ago
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This evolutionary shift happened quickly as dogs only split off from wolves a little over 30,000 years ago
The raised inner eyebrow movement in dogs is driven by a muscle which doesn't consistently exist in their closest living relative, wolves
2/2
The raised inner eyebrow movement in dogs is driven by a muscle which doesn't consistently exist in their closest living relative, wolves

An extraordinary new study, examining the anatomical differences between dogs and wolves, has revealed our canine companions recently evolved a very small facial muscle allowing them to raise their inner eyebrow. This tiny muscle was not found in wolves, suggesting dogs rapidly evolved this extra tissue to better communicate with humans.

The new research followed on from earlier study into the ways dogs facilitate eye contact with humans. Prior work has revealed humans favor dogs that perform certain facial movements, particularly an inner eyebrow raise (dubbed AU101 by researchers).

"This movement makes a dogs' eyes appear larger, giving them a childlike appearance," explains Bridget Waller, co-author on the new research. "It could also mimic the facial movement humans make when they're sad."

One fascinating early study discovered that dogs in shelters performing this particular facial movement were rehomed faster than dogs not utilizing this movement as frequently. Juliane Kaminski, co-author on the study, suggests this specific facial movement may have evolved in dogs to heighten the animals' bond with humans.

"The AU101 movement is significant in the human-dog bond because it might elicit a caring response from humans but also might create the illusion of human-like communication," says Kaminski.

This evolutionary shift happened quickly as dogs only split off from wolves a little over 30,000 years ago
This evolutionary shift happened quickly as dogs only split off from wolves a little over 30,000 years ago

So, to home in on whether this physical characteristic was truly an object of evolution from domestication, the researchers closely examined both the anatomical differences between dogs and wolves, their evolutionary predecessors, and also behavioral differences between the two in facial communications with humans.

Through close soft tissue examinations the researchers discovered a tiny facial muscle, called the levator anguli oculi medialis, was almost always present in domesticated dogs but almost completely absent in wolves. Behavioral studies then revealed dogs produced these AU101 movements at significantly higher frequencies and intensities than wolves.

"The raised inner eyebrow movement in dogs is driven by a muscle which doesn't consistently exist in their closest living relative, the wolf," says lead anatomist on the project, Anne Burrows. "This is a striking difference for species separated only 33,000 years ago and we think that the remarkably fast facial muscular changes can be directly linked to dogs' enhanced social interaction with humans."

It is hypothesized that dogs evolved this particular musculature trait as a way to selectively enhance their bond with humans who, either consciously or unconsciously, exhibited a preference for specific animals with these facial movements. One of the more fascinating elements in the study is the detection of such a rapid soft tissue evolutionary change. Obviously, changes in these kinds of tissues cannot be traced in fossil records so it is rare to be able to effectively home in on such a specific musculature adaptation. Even so, the researchers do suggest this is a fast evolutionary change, occurring over as little as 10 or 20 thousand years.

The study was published in the journal PNAS.

Source: University of Portsmouth

6 comments
toyhouse
And boy,...does it work! I'm sucker for it just about every time now that I think about it. Our Labrador has the trick down in spades and gets her way often enough. That look?,...when you're eating something they think you really should be sharing? I have next to zero will against her jedi powers. None of this surprises as k-9's have been our companions like none-other for centuries. Other than becoming their part-times slaves, I wonder what changes we've gone through - or maybe I just answered my own question?
McDesign
Totally agree - both our lab and border-collie-ish dog do it.
Username
Another backwards view of evolution. The dogs did not evolve this willingly in order to communicate with humans. Humans selectively bread dogs that showed this capacity to the point of standardizing it. Just like giraffes did not grow their necks to reach the higher leaves. The girafes with longer necks were better at surviving and mated with other girafes with longer necks reinforcing that trait. There is no "intent" in the process.
lasharela
Totally agree with Username. Does the author of the study know the meaning of the word "evolution?". 1. evolution is NOT RAPID. 2. evolution is not artificial selection. It sounds (and really is) very stupid that someone "finds out" something that everybody has known for millennia. Anyway, I like the fact that "popular science" has acknowledged the fact that animals do have facial expressions.
Kpar
This was mentioned on the Fox News Channel show "The Five". Called "puppy dog eyes", I do believe that this was part of an evolutionary development to bond dogs with humans. There was a recent experiment that showed humans selected wolves/dogs based upon their ability to interact successfully- I am sure this was part of the process. There is an old joke- A dog owners says to his dog, "I wish you were smarter, so you could tell me what you are thinking." The dog thinks, "If you were smarter, I wouldn't have to..."
Tacky-on
Thank you Username, for straightening out the terrible way this was written. It would be like saying women evolved large breast tissue to better manipulate men, which would only be true after the invention of plastic surgery and the silicone implant. In the case of dogs, it is a process of mutual domestication which has benefited both species massively. For a good understanding of how this works, watch the PBS Nova documentary available on Vimeo.com called, "Dogs Decoded". Truly excellent and shows the process of canine-human adaptations brilliantly, even if not this precise one.