STUDY: Dogs Are Experiencing an Unexplained Increase in Brain Size

Although contemporary dog breeds have not yet matched wolves in brain size, the gap between them is narrowing. The brains of modern dogs are enlarging, potentially due to their interactions with humans.

A study published in the journal Evolution examined brain sizes across both ancient and modern dog breeds. The researchers discovered that dog brain sizes increase the more genetically distant the breed is from wolves.

This was an unexpected discovery. “The results indicate that breeding modern dog breeds has been linked with an increase in brain size relative to ancient breeds,” stated Enikó Kubinyi, a senior research fellow at the Department of Ethology at ELTE Institute of Biology, in a news release. “We could not explain this increase based on the breeds’ roles or life history traits, so we can only hypothesize about the causes.”

The research team from Hungary and Sweden analyzed CT scans of over 850 dogs representing 159 breeds to reconstruct brain structures and measure brain volume. Their findings were compared to data from 48 wolf specimens.

The results revealed that a dog weighing the same as a wolf has a brain volume approximately three-quarters that of the wolf’s brain. This supports earlier research indicating that domestication reduces brain size by roughly 20 percent, as domesticated animals no longer need to hunt or protect themselves and face fewer dangers than wild animals.

“There is no necessity to maintain the metabolically expensive large brain, and the energy saved can be redirected toward other functions, such as producing more offspring,” explained László Zsolt Garamszegi, an evolutionary biologist at the Ecological Research Centre in Hungary, in the news release, “which is crucial for domesticated species.”

However, contrary to expectations, the study found that the more genetically distant a dog breed is from wolves, the larger its relative brain size becomes. This pattern held true regardless of whether the dog had demanding roles like herding or guarding.

“Possibly, the increased complexity of social environments, urban living, and adaptation to more rules and expectations have driven this change,” Kubinyi suggested, “impacting all modern breeds.”

The study also found no correlation between relative brain size and factors such as functional category, skull shape, lifespan, or litter size.

The researchers believe their conclusions are further supported by the independence observed in ancient breeds, which tend to bark less and respond less to human cues compared to modern breeds.

“Different dog breeds exist within varying degrees of social complexity and perform diverse complex tasks, likely requiring greater brain capacity,” said Niclas Kolm of Stockholm University in the news release. “Thus, we propose that selective pressures on brain size may differ within the dog species, and brain size variations among breeds may be linked to their roles or genetic distance from wolves.”