Around 5,000 years ago, dogs living alongside Neolithic farming communities in what is now eastern France had brains nearly half the size of the wolves sharing their landscape — a reduction more dramatic than the gap seen between modern wolves and dogs today.
The study, published in Royal Society Open Science, used CT scanning to reconstruct endocranial volumes across 185 modern and 22 prehistoric wolves and dogs, spanning a timeline from roughly 35,000 years ago to the present. The ancient dogs at the center came from Chalain, France, occupied between 5,000 and 4,500 years ago. Eight dog skulls from the site — a small but rare assemblage — showed a 46 percent reduction in brain volume compared to wolves living at the same time and place, putting them in the same range as modern toy breeds such as the chihuahua, pug, and Pekingese.
The researchers write, in the paper, that these results suggest “selection for small dogs may have begun in Europe during the Neolithic period” — thousands of years before the intensive breed standards of the modern era that many researchers had assumed were responsible for the most extreme reductions in dog brain size.
Many Neolithic dogs in this region, including those at Chalain, stood roughly 35 to 45 centimetres at the shoulder, with skull shapes resembling modern herding breeds. Their bones turned up scattered among food refuse rather than in burials, pointing toward a life closer to scavenging village dogs than valued working companions.
Thomas Cucchi et al.
At the far end of the timeline, the picture looked different. So-called “protodogs” from the Pleniglacial period — including a roughly 35,000-year-old specimen from Goyet in Belgium — showed no brain size reduction at all compared to contemporaneous wolves. The Goyet specimen actually displayed a slightly enlarged relative brain volume.
“Brain size increases, rather than decreases, might have occurred during the intensification of human and wolf interactions at the beginning of the domestication process,” researchers say. This possibly reflects the cognitive demands of adapting to proximity with humans or greater access to food resources. The dramatic shrinkage, therefore, occurred somewhere in the long gap between those early encounters and the established farming settlements of the Neolithic, a window that future research will need to fill with more specimens.
Recent neuroanatomical research links brain size reduction in dogs to a reorganization of brain tissue — less cortex, more subcortical structures — associated with heightened fearfulness, anxiety, a tendency to bark, and reduced trainability. Working from that framework, the researchers speculate that “these small Neolithic village dogs could have served the purpose of alerting for any unexpected changes in the settlement surroundings, given their inferred anxious temperament and higher reactivity to novelty.” Their bones found among consumed animal remains also raises the possibility they served as a food source, as dogs still do in parts of the world today.
One additional finding involves dingoes, introduced to Australia at least 3,300 years ago and since living largely independently of humans. Their brain volumes sit between the largest- and smallest-brained modern dogs — and larger than village dogs of comparable skull size — suggesting that thousands of years of living as wild apex predators may have partially offset the brain shrinkage that domestication typically brings.
Journal Reference: Royal Society Open Science. DOI: 10.1098/rsos.252453
