Domestic dogs have significantly smaller brains than their wolf ancestors. Researchers have long known that dogs’ brains shrank in the past, but when has been a mystery. Some theories also argue that strict aesthetic standards and intensive, selective modern breeding over the last 200 years could have been the cause.
In a new study, researchers from Europe have suggested that canines’ brains had already shrunk by at least 5,000 years ago — and possibly due to human interference.
During the Upper Pleistocene period, around 35,000 years ago, and long before humans started settled agriculture, dogs and wolves had similar brain sizes. This was around when humans and dogs began to interact more often. But by the Late Neolithic period, around 5,000 years ago, by when agricultural societies had become widespread, dogs living in Western European settlements had brains nearly 46% smaller than those of wolves at the same time, the researchers reported on April 29 in Royal Society Open Science.
They noticed this shrinkage in the remains of dogs in a Middle/Late Neolithic site in Chalain in France.
This study provides “new evidence” for the evolutionary reduction in the brain size of dogs that correlates with their domestication, Ian Kuijt, a zooarcheologist at the University of Notre Dame in Indiana, who was not involved in the research, said.
“It is fascinating to see the overall trajectory, even if this is a very small sample,” he added.
Virtual endocasts
To trace how dog brains evolved, Thomas Cucchi, a bioarchaeologist at the French National Centre for Scientific Research (CNRS), Paris, and his colleagues and peers analysed the skulls of 185 modern and 22 prehistoric wolf and dog specimens. The specimens included two dog-like animals from about 35,000 and 15,000 years ago, and Late Neolithic wolves and dogs from about 5,000 to 4,500 years ago.
The researchers used this data to create virtual endocasts — models of the space inside the skull where the brain once sat. Even though, the brain decomposes rapidly after death, the skull’s inner cavity preserves an imprint of the brain’s size and general shape, so the endocast served as a proxy for the brain, Eniko Kubinyi, a biologist at Eotvos Lorand University in Hungary and another author of the study, said.
Using the volume of these endocasts and the skull size, the team could track how brain size, relative to body size, changed at different points of time.
The endocranial volume of the so-called ‘protodogs’ from the Pleistocene didn’t indicate the smaller brain seen in later dogs. This, the researchers said, could mean they were still more wolflike than doglike.
One specimen from a cave site called Goyet in Belgium had a slightly larger brain volume than that of contemporary wolves. Dr. Cucchi said this might be due to increased human interaction at the beginning of the domestication process that posed new cognitive challenges.
Disproportionate drop
As humans transitioned from hunter-gatherers to a settled lifestyle around 5,000 years ago, dogs in Western European farming settlements adapted as well, becoming widely domesticated as a result.
Dogs face pressure to evolve from predators, foraging, and mating but domestication relaxes all of them. The high energy cost of neural tissues combined with the lower cognitive demands of a captive environment results in smaller brains in domesticated animals.
That said, the researchers found that dogs’ brains shrunk disproportionate to the drop in their body sizes — so much so that their brains were as big as those of Chihuahuas and pugs today. The researchers did note that the samples from Chalain alone were based on eight to ten dogs, meaning the findings from here alone can’t be generalised.
Previous studies have suggested that when brain size drops drastically, brain regions are reorganised. Often, this means a smaller cortical brain — which is responsible for learning, self-control, and cognitive ability — and a larger subcortical brain, which is involved in controlling emotions, Dr. Cucchi said.
Extrapolating from neuroanatomical research and studies of modern breeds, the researchers also suggested that the reorganisation resulted in dogs that were likely less trainable but more anxious, fearful, and prone to barking. Since small-brained dogs are more temperamental and wary of everything, they could have served the purpose of alerting humans to unusual activities nearby, Dr. Cucci said by way of one example of a role they could have played.
Dr. Kuijt noted that dog skulls and mandibles had also been found in refuse pits, meaning they were likely used as food as well.
A dingo story
“The link with changing temperaments serving as an alarm system is an intriguing speculation, but of course inferring behaviours from the archaeological and palaeontological records is challenging,” Michael Buckley, a bioarchaeologist at the University of Manchester and who was not involved in the study, said.
The study also examined dingoes, the East Asian dogs introduced to Australia and which returned to the wild at least 3,300 years ago. They have since been living largely independent of humans. Despite this long separation, dingoes’ brain volumes are between the smallest and largest-brained modern dogs, and larger than village dogs of comparable skull size.
According to experts, this suggests living as a free-ranging apex predator and facing the cognitive demands of hunting and survival without human support may have exerted some positive selection pressure favouring larger brains.
However, dingoes haven’t regained the brain size seen in wolves.
Even though dingoes could grow a larger brain, Dr. Kubinyi said, “brain tissue is metabolically very costly [to maintain], so brain size is unlikely to increase without strong selection pressure.”
Since dingoes do not rely on cooperative hunting against large and dangerous prey the way wolves do, “it seems that dingoes do not need a larger brain for their survival,” she added.
Jay Kakade is a freelance science writer.
Published – May 27, 2026 07:30 am IST
