"My aunt had a psychopathic brain, and she lived to be 90."

There was recently an interesting NPR story about a neuroscientist who studies the biological basis of psychopathy. The surprising twist is that he himself has genetic and brain activity indicators of being a violent psychopath! But, he seems like such a nice guy. The conclusion of the story is that we are not simply products of our biological determinants; environmental factors also play a very strong role.

And of course, that must be true. Just look at language. We speak a particular language because we have a genetic predisposition to do so, and then we were exposed to a particular language environment. The fact that nature / nurture arguments are still raging with regards to language, which is a pretty self contained system, makes me think that they will take a long time to be resolved for issues like psychopathy.

However, I think that one of the reasons this is such an interesting story is because it's emotionally satisfying, and that's not a good thing. It's too easy to hear this story and think, "He found this brain activity is related to psychopathy, but he has that brain activity, and he's not a psychopath. Therefore, people are magic."

First off, I don't know that Dr. Fallon has figured out the risk of psychopathy associated with having this brain activity. From what I understand from this NPR story and his TED talk, he's figured out that people who are psychopaths tend to have this particular brain activity, but I don't think he's done the study to figure out how many people with this brain activity are psychopaths. That second proportion is the necessary one to know in order to evaluate how surprising or unsurprising Dr. Fallon's peaceful existence is.

Secondly, as with almost all determinants of any kind of outcome, they only operate probabilistically. For instance, I think it's pretty much accepted wisdom that smoking is highly correlated with a variety of health problems. However, everyone also knows someone, the mythical aunt from the title of this post for instance, who smoked every day and lived to be very old. That's not contrary evidence to the fact that smoking causes health problems. In fact, it's expected that some people would have no health problems, all else being equal. That's the definition of probability.

So, even if the risk of psychopathy was very high given this brain activity (which again, it might not be), the fact that some one person with this brain activity is not a psychopath shouldn't be surprising, and doesn't really call the biological basis of behavior into question. The fact that he also happens to study the biological basis if psychopathy just happens to sex the story up.

The moral of the story is to think twice about science journalism that has an emotionally satisfying end to it.