How centuries of selective breeding have changed the shape of dogs’ brains

Erin Hecht says good breeding isn’t just about the skin.

The assistant professor of human and evolutionary biology at Harvard University has studied the brains of different breeds of dogs.

She found that humans who breed dogs for different purposes, such as herding or hunting, can physically change the shape of their brains. The discoveries were published Monday in the journal JNeurosci.

Hecht spoke to As it happens host Carol Off on her research. Here is part of their conversation.

What evidence do you have that different breeds of dogs not only have different bodies, they also have different brains?

In this study, we looked at MRI scans of dogs that went to a veterinary clinic for an exam and were found to be healthy. And we compared the brain anatomy of different breeds of dogs.

We wanted to see if the anatomy of the brain was different between races. And then, if so, what explains this difference? Is it the size of the body? Is it the shape of the head? Or could it be attributed to behavior?

And we’ve found that it appears to be. Behavioral selective breeding appears to have shaped the brain anatomy of dogs.

Researchers scanned the brains of different breeds of dogs to see how they were affected by selective breeding. (JNeurosci)

How significantly different is the brain of dogs?

This is one of the few times in science where I looked at the raw footage and just knew there was going to be something there, even before I did any statistics.

So you can actually see these differences if you just look at the scans themselves. Of course, we did a more complex analysis [but] to me it looks quite remarkably different.

Is this purely because dogs are bred differently? Many dogs were bred to work, to have a purpose. Is it just based on that or is it more than that?

I think it’s a combination of several factors.

One thing is that we bred them for different head shapes, and it affected the anatomy of the brain.

But we also bred them for different specialized behaviors, as you just mentioned. It seems we can see a trace of these behaviors in their brain anatomy. So there are circuits in the brain that seem to be linked to particular classes of behavior, such as herding or hunting.

A chihuahua is pictured on the streets of Friedrichsdorf, Germany. The brain of the little creature is actually not much smaller than that of a large dog like a Newfoundland. (Frank Rumpenhorst / AFP / Getty Images)

OKAY. So their brains are wired differently for functions like hunting or herding, or whatever. But at the same time, some of them have different sizes. Are some dogs just smarter than others because of their brain size?

Brain size varies from dog to dog, but not as much as you might think.

So Chihuahuas are, you know, really tiny compared to the size of a Great Dane. Their brains are not proportionately much smaller.

And as for the smartest breed, I think this research suggests that there are several different types of canine intelligence and that different breeds of dogs are specialized for different types of intelligence.

Is there a stupid dog?

I think in animal research it gets difficult when you try to measure something like intelligence – because the answer you get depends on how you define it and what kind of test you come up with to test it. This is a delicate question.

OK, that’s an unfair question. I guess the smallest dog in the world is supposed to be a chihuahua, which is only four inches tall. And then there are these big giant Newfoundlanders. Do you see a big difference … not just in size, but in wiring between a Chihuahua and a Newfoundland?

The conclusions are preliminary. This is only the first study to examine whether there is variation in brain anatomy. I don’t want to be too confident about the specific differences between specific breeds yet. But it appears that behavior-selective breeding appears to influence the brains and anatomy of different races in different ways.

In this study, the dogs we had, as far as we knew, were all just pets – they weren’t actively working. So the differences we were able to spot were the differences that were still there despite not being working dogs.

In our current research, we are looking at dogs that are actively doing the jobs the breed was created to do. And so we hope – or think – that we could see even more pronounced differences in these actively working dogs.

Jennifer Glen and her flock of border collie Grit sheep in Soldier Hollow, Utah. Researchers are now examining how the brains of working dogs might differ from that of pets. (Natalie Behring / AFP / Getty Images)

So you compare, say, the brain of a border collie that’s doing its job and the one that’s on the couch and doesn’t have a job, and you could see that you could see some profound differences in the way brains are wired?

Yeah. So we hope to look at the two between the races. If we could get, you know, 50 border collies – how much variation do we see within border collies? How does that relate solely to breeding skills, and how does that compare to, say, 50 beagles?

We now know what people expect, mainly from dogs. They want a loyal, loving pet that is good with children, right? So, do you think the continued evolution of these dogs will go in this direction?

If we selectively breed them for this behavior, then I think it’s reasonable to assume that we’ll continue to change their brains. And the way they are changed now may have more to do with the family life of pets and then work.

Interview conducted by Kevin Robertson and Kate Cornick. Questions and answers edited for length and clarity.


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Jeanetta J. Stewart