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Oxytocin and the genetics of altruism

Where to publish a paper on the genetics of altruism? In an open-access journal, of course! One day after publishing the fossil primate paper that's creating so much excitement -- it's a great fossil, but too old to tell us anything about our recent ancestors, shared with other apes, or the less-recent ones shared with monkeys -- PLoS One published "The Oxytocin Receptor (OXTR) Contributes to Prosocial Fund Allocations in the Dictator Game and the Social Value Orientations Task", by Salomon Israel and colleagues. Like all papers in open-access journals, the full text is available on-line.

These researchers measured altruism in 200 students, based on how each chose to divide a pool of money with another unknown individual. Their hypothesis, based on various past studies, was that the hormone oxytocin is important for social interactions in general and for human altruism in particular. For example, Zak and colleagues showed that sniffing oxytocin made people offer a more generous split when the recipient had the chance to retaliate for a low offer (the "Ultimatum Game"), although not when there was no chance to retaliate, as in the Dictator Game used in the current study.

The researchers tested for statistically significant relations between and different variants of the oxytocin receptor gene, which codes for the protein that responds to this hormone signal in the brain, and "prosocial responses" (generosity) in the Dictator Game and a more-complex version, the SVO. Interestingly, none of the genetic differences they looked at were in the protein-coding part of the gene (orange). Most were in an intron, which would be transcribed from DNA into messenger RNA but then cut out before the mRNA is translated into protein. So I assume these genetic differences could affect how much oxytocin receptor protein is made where and when, but not the structure of the protein itself.

Generosity depended most strongly on whether a DNA base shortly after the protein-coding region (rs1042778) was a guanine (G) or a thymine (T). The difference was statistically significant, but also fairly small (5.1 vs. 5.5). So choosing a mate (or a business partner) based on this genetic difference might be premature. I see two possible explanations for these results. Maybe even a large difference in the amount of receptor protein has only a small effect on generosity. Alternatively, maybe this specific difference (and other genetic differences studied, some of which also had significant effects on generosity) has only a small effect on the amount of receptor protein made. In that case, there could be other genetic differences (perhaps not included in the study group) that would have a larger effect.

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