New study looks at why dog brains are getting bigger

cross section of dog's skull with brain and nasal cavities shown

Dog brains are much smaller than wolf brains, but new research suggests modern breeding efforts have somewhat increased their relative size.

a cross section of a dog's skull with brain and nasal cavities
A dog’s brain

Compared to ancient dogs, modern breeds that developed in the past 150 years possess larger skulls compared to their body size. Yet scientists still don’t know why.

The research team found that dog brains are getting larger the further genetically that they have evolved away from a wolf.

That was a startling finding. “The results show that the breeding of modern dog breeds has been accompanied by an increase in brain size compared to ancient breeds,” Enikó Kubinyi, a senior research fellow at the Department of Ethology at ELTE Institute of Biology, says in a news release. “We couldn’t explain this based on the tasks or life history characteristics of the breeds, so we can only speculate about the reasons.”

In the study, a team from Hungary and Sweden used CT images of over 850 dogs representing 159 breeds to reconstruct different individuals’ brains and determine their brain volume. They compared the findings to 48 wolf specimens.

While the size of a wolf’s brain is 24 percent larger than that of a similarly sized dog, the more that a dog breed differed from a wolf, genetically speaking, the larger their brain.

The findings suggest that while dog domestication thousands of years ago might have initially shrunk parts of the dog brain – like those related to mate choice, predators, or hunting – modern breeding has triggered some modest cognitive growth in the past century and a half.

But how?

“Different dog breeds live in varying levels of social complexity and perform complex tasks, which likely require a larger brain capacity,” says evolutionary biologist Niclas Kolm from Stockholm University in Sweden.

Kolm and his colleagues hypothesized that some dogs, bred by humans for more complex tasks like herding or sports, would have larger relative brains.

That was not the case. Instead, the only factor that seemed to impact the relative brain size of modern dog breeds was how different their genes were compared to wolves – not the function of the breed, its litter size, or its life expectancy.

Previous research, for example, has found that dogs more closely related to wolves are worse at communicating with humans.

To learn more about how ancient and modern dog brains differ from wolves, the team suggests future research should compare the size of different brain regions.

Perhaps then scientists can figure out what impact we’ve had on dog brains and behavior.

The study was published in Evolution.

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