We are nihilists, Lebowski! We care for nothing!

I commented a while ago on something that Dean Ornish calls genetic nihilism, a great turn of phrase that I will deftly procure for myself. This is a sort of view in which we say "well, my DNA has already programmed my health and/or behaviour, whether I will get diabetes or cancer or an aneurysm while doing backstroke in the community pool." Which, in addition to being untrue, is a pretty irresponsible way to live.

I thought of it because of a Swedish study showing that the presence of a certain variant of a gene in males is associated with increased prevalence of "marital crisis" in the last 12 months, reduced proportions in number of men married, and lower scores on a sort of "pair-bonding index." And the headlines were awesome - "Why men cheat" (Science Magazine), or "Commitment phobes can blame genes" (BBC). These are great examples of genetic nihilism. We are expected to take it at face value that men fear commitment and cheat on their wives and girlfriends, and furthermore that these are parts of being male programmed into DNA as much as a penis is, so we should be able to find a gene that makes it so.

No one is ever going to find that gene, because it doesn't exist (along with the "penis gene"). The authors of this study do some fancy calculations and say that about 28% of the variation they saw in the study were inheritable from their parents. Now, I'm going to say that heritability is not just a question of genes being passed down, and if you want to argue about that let me know. The rest is from "environmental factors," which is to say everything other than your parents.

We have roughly 25 000 protein-coding genes in our cells. Let's say 1% are involved in mating behaviour, which is probably a ridiculous underestimate given the importance of mating to continuing the species. That's 250 genes involved in mating behaviours, which are only the genetic part of their heritability measure, which in turn only accounted for about 28% of the variation in the study. While some of these genes might be more important than others, the assertion that a different version of a single gene will double your chances of being unmarried or in a turbulent relationship seems unlikely at best.

This study does have an interesting design, however, involving some 500 same-sex twins both married and unmarried. I hope they run some fishing trips (technical term: gene microarray) looking at polymorphisms on other genes that might be related.