Dogs’ brains began to shrink at least 5,000 years ago, study finds | Evolution

It’s long been known that dogs have less space between their ears than wolves, but research now suggests their brains started getting smaller at least 5,000 years ago.

Experts say the findings offer new insights into the domestication of our canine companions. However, these findings are unlikely to explain why your spaniel only drinks from a mud puddle: Researchers say a reduction in brain size does not mean dogs are dumber than their wolf-like ancestors.

“The way our dogs live today does not give them the opportunity to always express the essence of their intelligence,” said Dr. Thomas Cucchi, first author of the study from the National Center for Scientific Research.

“But they are extremely intelligent and domestication has not made them stupid, but made them actually able to read us and communicate with us.”

The relationship between humans and dogs is ancient, with research revealing that the oldest direct genetic evidence relating to domestic dogs dates back more than 15,000 years.

But although reduction in brain size is generally considered a hallmark of domestication, there has long been debate over exactly when dogs ended up with smaller brains than wolves, with some experts suggesting it may have happened early in the dog-human relationship.

However, others argue that reduced brain size is not a feature of domestication but rather reflects the emergence of purebred breeds over the past 200 years.

Writing in the journal Royal Society Open Science, Cucchi and colleagues studied CT scans of the skulls of 22 prehistoric wolves and dogs, dating from 35,000 to 5,000 years ago, as well as CT scans of the skulls of 59 wolves and 104 modern dogs. These included various modern breeds as well as stray or “village” dogs and dingoes.

The researchers used these analyzes to track changes in brain size over the evolutionary history of dogs.

The results reveal that, taken together, modern dog breeds, dingoes, village dogs and Late Neolithic dogs had brains 32% smaller than those of ancient and modern wolves.

Specifically, dogs that lived in the late Neolithic – about 5,000 to 4,500 years ago – had brains 46% smaller than wolves from the same period, with brains of a similar size to today’s pugs. Further work revealed that these dogs had significantly smaller brains than ancient wolves, even when taking their body size into account – an important consideration given that they were smaller overall..

However, the team found no sign that the brains of two dogs that lived alongside humans 35,000 and 15,000 years ago – sometimes called “protodogs” – were smaller than those of these ancient wolves. Indeed, one brain was relatively larger, with the authors suggesting that this raises the possibility that brain size actually increased in the early stages of domestication.

Cucchi said it was unclear why domestication gave rise to dogs with smaller bodies and brains than their wolf-like ancestors.

However, he noted that research suggests that when the brain is reduced in size, it reorganizes, meaning small dogs are less trainable and more wary of changes in their environment, potentially making them useful as “alarm systems.”

But Cucchi said it could also be that limited food resources in the Neolithic village environment favored smaller dogs with smaller brains, because these required less energy.

Dr Juliane Kaminski, an expert in canine cognition at the University of Portsmouth who was not involved in the study, said a particularly important revelation was that “protochians” did not have smaller brains than wolves.

“They did not yet show this sign of domestication that we thought they were [a] is an integral part of this domestication syndrome,” she said.

Kaminski said the study suggested that the relationship between humans and dogs may have started out rather loosely before developing into a very strong bond.

“What [the authors] I’m just saying: OK, the timeline for the onset of full domestication syndrome may be a little later than the genetic data suggests,” she said.