The sad, supplicating, and superciliary expression that dogs make is so familiar that we have made it an idiom: puppy's eyes.
A new study suggests that this is yet another example of dogs' ability to communicate with people, a phenomenon that has evolved as animals were domesticated from old wolves, there is less than 15,000 years.
An elevation of the internal eyebrow is caused by a specific muscle that makes the dog's eyes appear larger and more like a child's and gives an appearance similar to that of a human when that it's sad. The researchers found that, while six dead dogs, they had dissected this muscle in a uniform manner, four dissected wolves did not have it or hardly. They also found that 27 guard dogs in the UK raised their eyebrows much more often and intensely when interacting with strangers compared to nine wolves in two wildlife parks in the UK.
This suggests that old canines with expressive eyebrows may have been able to attract the attention of humans, write the authors, and that this care would have given animals an advantage in terms of selection allowing them to pass on dogs' eyes. -chiots to their descendants. The study was published in the journal Proceedings of the National Academies of Sciences.
"What is so provocative in this discovery is the likelihood that our subconscious biases have shaped the evolution of the dog's eye muscles," said Brian Hare, Duke University's evolutionary anthropologist and expert on Canine cognition, who led the study but did not participate in the research. . "The presence of these anatomical differences between wolves and dogs is a firearm for the role of our desire to cooperate and communicate with dogs, who are a driving force in their evolution."
The new research builds on previous work by authors examining this muscle movement in dogs. One study found that shelter dogs that raised the interior eyebrow were adopted faster than those who did not, in a kind of modern demonstration of the power of puppy eyes on humans. Another study found that dogs do more puppy eyes when people watch.
"It's just this kind of behavior that drives many dog owners to say to themselves:" Oh my God, they want something. What do they need? ", Said Burrows, biological anthropologist at Duquesne University.
Like all the physical variations observed in a species essentially designed by humans, the development of this muscle of the dog's eye was extremely fast, she added: "I speculate here, but the Domestication process must produce evolutionary changes in the dog much faster than evolutionary changes, which you would see in the wild. "
Regarding dog-human relationships, the eyes are important. Dogs make eye contact with people when a problem prevents them; the wolves do not do it. The researchers found that when they looked at each other in the eyes, both humans and dogs experienced an increase in oxytocin levels – "the hormone of love". The same thing happens when the mother and the baby make eye contact.
The new study also identified another facial difference between the wolf and the dog. A muscle that pulls the eyelids to the ears, which, says Burrows, occurs when dogs pant and seem almost "smiling," was present in all but one of the dissected dogs: the Siberian husky, an older breed that is more closely related to wolves. Three of the four dissected wolves had it, but it was thinner and probably weaker, according to the study.
The discovery of the eyebrows raises the possibility that puppy eyes are not a thing chosen by humans, but rather a by-product of domestication. A long-term study of the domestication of silver fox has shown that certain physical traits – loose ears, curly tails, and mottled coat colors – accompany the walk when people choose the calmer animals for breeding. That's what is called domestication syndrome, and it's possible that raising the eyebrow of dogs is a part of it, said Burrows.
"Domestic dogs were created by humans and we have clearly selected species that would not bite us or bite our children," Burrows said. "So, all this domestication syndrome has characteristics that are all interrelated."
Clive Wynne, a behavioral scientist who heads the Canine Science Collaboratory at Arizona State University, has described this study as "very interesting, original and challenging." But to be more convinced, he said, he would like to see the results of a larger sample including more breeds of dogs and subspecies of wolves, as well as wolves and dogs at various levels. from experience with the man.
"Although evolution (domestication) has obviously led to crucial changes between dogs and their wolf ancestors, the way an individual behaves at any time is also due to his or her individual life experiences," writes Wynne. in an email. "A study that describes the behavior between dogs or wolves and people must explain the experiences of those tested."
Burrows said she and her co-authors intended to continue research, including examining other breeds of dogs, coyotes and domestic foxes. The shape of a pug's face looks nothing like that of a collie, she noted.
"This will potentially dictate how the face can move," she said. "As we develop our study and really focus on what the musculature looks like … I'm really interested to see what kinds of differences we can deepen."