AVPR1a polymorphism tied to variation in altruism

Individual differences in allocation of funds in the dictator game associated with length of the arginine vasopressin 1a receptor RS3 promoter region and correlation between RS3 length and hippocampal mRNA:

Since variation in the length of a repetitive element in the vole AVPR1a promoter region is associated with differences in social behavior we examined the relationship between RS1 and RS3 repeat length (base pairs) and allocation sums. Participants with short versions...of the AVPR1a RS3 repeat allocated significantly...fewer shekels to the 'other' than participants with long versions....

This is basically a study which explores behavioral economic questions with the methods of behavior genetics. The interesting point is that the same tendencies on this locus correlated with the number of repeats on the gene can be found in both voles and humans, suggesting that the same switches can modulate complex behavior across many taxa. Here's a link for SNPs on this gene. ...