On nature and nurture and their interactions to make a personality

My mom called me yesterday because she had experienced some Science and was excited about it. She was watching a TV episode about aggression and how it appears in nearly every species. She called me to say that she thought my lab should look for the gene for aggression. “It should be easy,” she said, “because it should be the same gene in every animal.”

Aggressive silver fox

Yeah, you’d think that there would be single genes controlling bits of our personalities (human and dog — I think dogs are much more interesting, but in this case it’s much the same problem). Only ten or twenty years ago we thought we were in the endgame to find these genes: once the human genome was sequenced, we expected to be able to do a series of big studies to find these answers. Take a few hundred humans and sort them into “violent“ and “not violent.” Then look at markers in their genomes and use computers to find associations: all the violent people should share one marker, which will tell you where the gene for violence is. Done.

But we did those studies and we found, again and again, that these sorts of personality traits don’t give up their answers this way. In fact, in the case of zero personality traits have we found one (or even two or three) genes that control that trait. Sometimes we find genes that we think control a solid chunk of a trait, only to find that it was a statistical error — if you ask enough questions, you’ll find an interesting set of data just by chance. But if you ask the same question of another set of data (in other words, do another study), you’ll see that the first one was wrong. And this is what we have seen, for trait after trait.

Now, occasionally we’ll find a personality trait for which a little bit of it can be explained by one gene. When I say a little bit, I mean that if there is a normal amount of variety in this trait — say, in how violent a person is, ranging all the way from a pacifist to a psychopath — then the genes we find will explain about 0.1 percent of that variety. The rest is — what? Chance? Environment?

It’s a bunch of things, probably. For one thing, it’s surprisingly hard to define a personality trait. What’s violence? In dogs, we diagnose different kinds of aggression: territorial aggression, owner-directed aggression, dog-dog aggression, fear aggression. Are these all the same thing? Probably not. So instead of looking for one trait, “aggression,” should we look for four traits? Maybe. But do we actually know that those are the right four? Maybe there are six. Maybe there are ten. Maybe there are a hundred. We need to understand the traits we study better, and ask more detailed questions about them.

For another thing, yes, environment is important! Genes are important, but they are nowhere near the whole story. And environment is complicated. Certainly the difference between a pet store puppyhood and early life with a responsible breeder is huge. But can you lump early life experience into two bins, “good” versus “bad”? There are all kinds of variables. In the pet store, what kind of crate was the puppy kept in, how much interaction did it get, how young was it when it arrived? At the breeder’s, were there other adult dogs besides the mother to interact with, were there any small children, were there any bad interactions with other dogs or people? And a hundred, a thousand more questions.

I read recently about a pair of conjoined twins with very different personalities. These two had the same genes, because they came from the same embryo originally. And they had the same environment, because due to being conjoined they had to spend their lives in each other’s company. So how could their personalities differ? The article theorized that they reacted to each other, with one taking a bold, outgoing role and the other becoming shy and retiring in compensation.

And finally, the most interesting idea, in my opinion as a genomics researcher: what if we aren’t going to find the answer by looking at the sequences of DNA that make up genes? What if we are going to find the answer by looking at how the genes are regulated? If it isn’t that my dog is more fearful because some gene is a little broken, but she is more fearful because some gene is getting turned on much more or much less often than it should? It’s hard to investigate gene regulation when you have questions about the brain, because to do it you kind of have to get inside the brain, and it’s hard to do that without killing the person you’re studying. But I think looking at regulation is where things are going to have to go, and researchers are working on finding non-lethal ways of doing it.

So, nature and nurture: both important. Personality: super, super complicated. But also wicked interesting.

[If you’re a dog trainer or just interested in dog genetics, you can learn about the genetics of dog behavior with me this summer in an online course with the APDT!]