New study finds the brains of modern-day dogs are getting bigger

The preparation for this study took several decades

Tibor Csörgő, a senior research fellow and a co-author in the study, has been collecting canine skulls for decades. The team analyzed the CT scans of the skulls of 159 contemporary dog breeds to estimate the brain cavity volume, with 48 specimens representing wolves.

As per the results published, wolves with an average body weight of 68 pounds (31 kilograms) have an average brain volume of 131 cm3, in comparison to the dogs in the similar weight category who have an average brain size of 100 cm3. 

Although this confirmed that domestication has had a similar effect on the brain size as observed in other species, the team was perplexed to discover that the more distantly a dog breed is genetically linked to wolves, the larger the size of its brain would be.

Enikő Kubinyi, the co-author of the study, speculated that the brain size change in modern breeds might be due to the more complex social environment, urbanization, and adaption to more roles and expectations that come from living with humans.

“The results show that the breeding of modern dog breeds has been accompanied by an increase in brain size compared to ancient breeds. We couldn’t explain this based on the tasks or life history characteristics of the breeds, so we can only speculate about the reasons,” added Kubinyi in a statement.

The study suggests that potential links between brain structure and other traits in dogs could be enhanced in future studies in the field of brain evolution in dogs.

The study results were published in the journal Evolution.

Study abstract:

Domestication is a well-known example of the relaxation of environmentally based cognitive selection that leads to reductions in brain size. However, little is known about how brain size evolves after domestication and whether subsequent directional/artificial selection can compensate for domestication effects. The first animal to be domesticated was the dog, and recent directional breeding generated the extensive phenotypic variation among breeds we observe today. Here we use a novel endocranial dataset based on high-resolution CT scans to estimate brain size in 159 dog breeds and analyze how relative brain size varies across breeds in relation to functional selection, longevity, and litter size. In our analyses, we controlled for potential confounding factors such as common descent, gene flow, body size, and skull shape. We found that dogs have consistently smaller relative brain size than wolves supporting the domestication effect, but breeds that are more distantly related to wolves have relatively larger brains than breeds that are more closely related to wolves. Neither functional category, skull shape, longevity, nor litter size was associated with relative brain size, which implies that selection for performing specific tasks, morphology, and life history does not necessarily influence brain size evolution in domesticated species.