One of the big unsolved mysteries in evolutionary theory is why creatures are altruistic. Selflessness doesn’t seem to be one of those qualities that ensure survival of a bloodline, since, by definition, it means acting against oneself. And genes, as Richard Dawkins has famously suggested, are pretty selfish. So, how come we still have customers jumping over fast-food counters to save an employee from a gun-wielding nutjob? Or ants that raise other ants’ children? A new study in the British Journal of Psychology makes the case that it’s because some females of the species are genetically predisposed to prefer altruistic mates.