The wolf relatives of modern-day dogs began the evolutionary process of becoming humans’ best friends more than 10,000 years ago. Scientists still don’t know the whole story behind how and why domestication of dogs occurred, despite over a century of research. Now a new study published on Thursday in Scientific Reports reveals genetic changes that may have allowed ancient dogs to feel comfortable around humans by lowering the stress levels the animals experienced in our presence.
” This is the first genetic evidence that supports the hypothesis of mutations in stress response system initiating canine domestication,” said Miho Nagasawa (animal scientist at Azabu University, Japan).
Nagasawa and her colleagues recruited the owners of 624 dogs to enroll their pets in a study consisting of two behavioral tasks. The researchers divided the dogs into two categories. The first group consisted of breeds that were considered to be closely related to wolves such as Siberian huskies and Akitas. The second consisted of other breeds that were more distantly related than their wild relatives.
The first task required the dogs to use clues from researchers (such as their gaze direction or a pointed finger) to determine which bowl contained a treat. This task was to test how well dogs understand human communicative signals. And it built on past findings that even very young domesticated-dog puppies are better at understanding human signals than adult wolves raised by people. The researchers found no difference in performance between ancient and modern dog breeds. This is as expected.
The second task was to open an inaccessible container to get delicious-smelling food. The researchers measured how much time the frustrated canines spent gazing back at them for help–another behavior that wolves are less adept at than dogs. The scientists found a significant difference in the behavior of the two groups. The closer wolf relatives spent less time looking back at human experimenters. This could be interpreted by the authors as a sign that more recent dog breeds have a greater social attachment to humans.
After completing the tasks, researchers looked at four genes in their canine subjects and found differences that could relate to their relationships with humans. The team also looked at genes that produce oxytocin, a hormone that is associated with social bonding, and cortisol which is a key stresshormone. Scientists discovered mutations in a cortisol producing gene that were different between the ancient and modern dog breeds. This finding also reflects a previous study that revealed lower cortisol levels in foxes that were selectively bred to be less fearful and less aggressive toward humans.
The authors speculate that the lower stress levels played a part in dog domestication due to the correlation between cortisol-producing gene changes and the older dog group’s less social-cognitive abilities. A dog should be less anxious around humans in order to develop the social-cognitive skills necessary to interact with and communicate better with humans.
” Although it isn’t clear if cortisol, which is a stress marker, is lower in dogs than wolves, the fact there were two genetic mutations that were detected–one of them accompanied by changes to the production of intracellular Cortisol- may provide clues as to how canine tolerance and adaptability to human society was achieved,” Nagasawa said. Nagasawa and her colleagues are currently conducting follow-up research in order to determine if cortisol levels differ between the two breeds.
The Scientific Reports study presents “exciting new evidence that dogs’ unusual ability to cooperate and communicate with us evolved as a result of natural selection favoring wolves who could approach and eventually show friendly behavior toward humans,” says Brian Hare, a Duke University evolutionary anthropologist, who was not involved in the study.
But Maria Lahtinen (a visiting scholar at Finland’s Museum of Natural History) questions whether the new findings can be applied to ancient dogs. She says, “The problem with this study is that the researchers have used modern dogs in order to study the past.” “I wouldn’t take this study as an indicator of anything from the past, but as an indicator of how modern dogs behave
Hare suggests that future research could focus on other ancient breeds of dog. This would help to overcome this problem. For example, if the gene identified in the new study did indeed play a significant role in enabling dogs to communicate with humans in a new way, he says, then “it should be that dingoes and New Guinea singing dogs also show the same relationship between their use of human gestures and this genetic candidate.”