Photo-Illustration: Photo: Stefanie Grewel/Corbis

Slowly but surely, we’re learning more about how dogs perceive the world — and us. For example, Emory University’s Dog Project (a.k.a. the best part of Emory University) has already identified special regions in doggy brains that appear to have the function of recognizing dog and human faces.

What we don’t know very much about is how dogs react to seeing a face — how they interpret its expression and so on. But now, in a paper published in the journal PLOS ONE, a team from the University of Helsinki claims to have conducted what they say is not only the first-ever research on the specifics of how dogs respond to faces displaying different emotions, but the first-ever article on how any non-primate animals do. The study offers some fascinating insights into the co-evolution of humans and dogs — and some hints at which traits helped certain dogs survive the transition from being majestic, wild hunters to man’s best friend.

For the study, led by Sanni Somppi, a member of the university’s Department of Equine and Small Animal Medicine, the researchers brought 33 dogs into their lab that had previously been trained to sit in front of a monitor and rest their heads on a little doggy chin rest. (The team, apparently wary of the potential PR ramifications of “conducting experiments” on adorable pooches, stated multiple times that no dogs were harmed in this experiment — “they were not restrained or forced to perform the task” and were given frequent rest breaks and rewards.) Then they showed each dog a block of 8 to 12 images, each flashed for a second and a half, of either a dog face or a human face in predetermined “threatening,” “pleasant,” or “neutral” expressions. (Half of the human faces were male and half were female, represented evenly among the different expressions, and the faces of 25 different dog breeds were shown.) The order of the images was randomized, and the test was carried out over two days.

Researchers measured which “areas of interest” dogs looked at most: eyes, midface (nose or muzzle), mouth, inner face (eyes, midface, and mouth), or whole face. They also recorded “entry time” (how long it took a dog to fixate on one feature when it first saw the image), and “orientation of initial attention” (where the dog looked first). Data in hand, the researchers crunched the numbers.

Notably, the dogs responded to “threatening” faces — squinty eyes, wrinkled nose, open mouth — quite differently depending on whether they were human or canine. Threatening human faces elicited an “avoidance response,” meaning the dogs avoided looking at them, which researchers hypothesize is because domesticated dogs have learned to act submissively toward humans (if you’re threatened by someone higher than you in a social hierarchy, you don’t want to antagonize them further by maintaining eye contact). The same type of facial expression in fellow dogs triggered the opposite response; instead of looking away from a threatening dog, another dog will pay it extra attention, possibly to gauge how serious the threat is and so on.

A graphic from the paper showing the Areas of Interest (AOIs) to which dogs’ gazes were drawn in response to various canine and human facial expressions. The “hotter” the color, the longer the dogs’ gazes fixated on a particular area.

The results also showed that dogs usually fixated on eyes first, regardless of whether the face they looked at belonged to a human or a fellow dog. This, suggests the researchers, could mean that dogs convey meaning through eye contact just like humans and many primates.

The researchers postulate that co-evolution can explain some of what they found. “The tolerant behavior strategy of dogs toward humans may partially explain the results,” Somppi said in the study’s press release. “Domestication may have equipped dogs with a sensitivity to detect the threat signals of humans and respond to them with pronounced appeasement signals.” (I know how mad at me you are about the couch I destroyed — can’t you see how remorseful I am by my body language?)

If all this is correct, it tells — or at least implies — a fascinating story. As humans and dogs co-evolved, their relationship radically altered which criteria determined those canines that would live and be able to pass on their genes, and those that wouldn’t. To a certain extent, dogs had to get with the human-dominated program or get kicked off the evolutionary train. Dogs that survived were, well, Good Boys — they were the most sophisticated at keeping an eye on the emotional states of the humans around them and were always vigilant about not pissing off their masters, as this could mean getting cut off from stuff that would help them survive and reproduce — food, (presumably) access to mates, and so on.

It’s important to note that no one study, especially a first of its kind, can definitively tell a story like this, but these are tantalizing clues. Dogs’ behavior toward humans did come from somewhere, after all. So the next time your dog makes an exaggerated display of sorrow or submissiveness, keep in mind that he isn’t just being dramatic — he might be exhibiting the results of millennia of co-evolution.