How centuries of selective breeding has changed the shape of dogs' brains

Erin Hecht says that good breeding is more than just skin deep.

The assistant professor in human and evolutionary biology at Harvard University has been studying the brains of different dog breeds.

She found that humans breeding dogs to serve different purposes — such as herding or hunting — can physically alter the shapes of their brains. The findings were published Monday in the journal JNeurosci.

Hecht spoke to As It Happens host Carol Off about her research. Here is part of their conversation. 

What evidence do you have that different dog breeds don't just have different bodies, they also have different brains?

In this study, we looked at MRI scans from dogs that came to a veterinary clinic for an examination and turned out to be healthy. And we compared the brain anatomy across different breeds of dogs.

We wanted to see if brain anatomy was different across different breeds. And then, if so, what accounts for that difference? Is it body size? Is it head shape? Or could it be attributed to behaviour?

And we found that that appears to be the case. It seems like selective breeding for behaviour has shaped dogs' brain anatomy.

How significantly different are dogs' brains?

This is one of the few times in science when I've looked at the raw images and just known that there was going to be something there — even before doing statistics.

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

Is it purely explained by the fact that the dogs are bred differently? Many dogs were bred to work, to have a specific purpose. Is it just based on that, or is it more than that?

I think it's a combination of multiple factors.

One thing is that we've bred them for different head shapes, and that has affected brain anatomy.

But we've also bred them for different specialized behaviours, like you just mentioned. It does look like we can see a trace of those behaviours in their brain anatomy. So there are some circuits in the brain that seem to be linked to particular classes of behaviour, like herding or hunting. 

OK. 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 other dogs because of brain size?

Brain size does vary across dogs — but not as much as you would think.

So Chihuahuas are, like, you know, really tiny compared to the size of a Great Dane. Their brains are not proportionally that much tinier.

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

Is there such thing as a dumb dog?

I think in animal research it gets tricky when you try to measure something like intelligence — because the answer that you get depends on how you define it, and what kind of test you make up to test it. That's a tricky question.

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OK, it's an unfair question. I guess the smallest dog in the world is supposed to be a Chihuahua, who's only four inches tall. And then there's these big giant Newfoundlands. Would you see a big difference ... not just in size, but in wiring between a Chihuahua and a Newfoundland?

The findings are preliminary. This is just the first study to look at whether there is variation brain anatomy at all. I don't want to get too confident yet about specific differences between specific breeds. But it does look that way, that selective breeding for behaviour seems to influence different breeds' brains and anatomy in different ways.

In this study the dogs that we had, as far as we know, were all just family pets — they weren't actively working. So the differences that we were able to pick up on are the differences that were still there despite the fact that these weren't working dogs.

In our current research, we are looking at dogs that are actively doing the jobs that the breed was created for. And so we're hoping — or we're thinking — that we might see even more pronounced differences in these actively-working dogs.

So you're comparing, say, the brain of a border collie who's out doing the job and the one who's on the couch and doesn't have a job, and you might see you might see profound differences in how brains are wired?

Yeah. So we're hoping to look both between breeds. If we could get, you know, 50 border collies — what is the amount of variation we see within border collies? How is that linked just to skill at herding, and how does this compare to say 50 beagles?

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We know what people want now, mostly, from the dogs. They want a loyal, loving pet who's good with kids, right? So do you think that the continuing evolution of these dogs will be in that direction?

If we are selectively breeding them for that behaviour, then I think it's reasonable to think that we will continue to change their brains. And the way that they're being changed now is maybe more related to family pet life and then to working life.

Interview produced by Kevin Robertson and Kate Cornick. Q&A edited for length and clarity.