Why the new paper by Christakis and Fowler on friendship makes me queasy

I am a neuroscientist, and as a neuroscientist I have a strange belief that most of who we are comes from our brains. My entire career is based around understanding the neural basis of behavior which, I think, is pretty justifiable.

So when I see paper looking at the genetics of behavior, I expect to see at least one or two genes that are directly involved in neural function. A dopamine receptor, probably, or maybe some calcium channels that are acting up. And in one recent paper looking at schizophrenia, that’s exactly what we find! A D2-like dopamine receptor and some glutamate genes. My world is consistent.

But then we get a paper about friendship from Christakis and Fowler who find that friends are more likely to be genetically related to you than chance. So that means that your close friend? Basically a fourth cousin. What Christakis and Fowler have found is a few sets of genes that seem like they might influence friendship. The most important is an olfactory gene which just reeks of pheromones (or possibly hygiene). But the next most important genes? They have to do with linoleic metabolism and immune processes!

Now what am I, as a neuroscientist, supposed to do with that? How do I reconcile my neural view of the world with one where metabolic processes are influencing decisions?

Perhaps I can quiet my mind a little. In a past blog post, I wrote about how social status causes changes in genes related to immune processes. So maybe I can squint and say that okay, really this is an epiphenomenon relating to social status.

But if I’m going to understand behavior – what do I have to know? Do I have to understand literally all of biology? That traits and choices are being affected by what seem to be totally non-brain factors? That my philosophical position of the extended mind is maybe true? That makes me a little queasy.

(End massively speculative rant.)

References

Christakis NA, & Fowler JH (2014). Friendship and natural selection. Proceedings of the National Academy of Sciences of the United States of America, 111 (Supplement 3), 10796-10801 PMID: 25024208

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