A time-honored method of creating moral outrage against a public figure is the sex scandal. But is this about morality or is it just about the biology of our selfish genes?

It’s a complex thing to be a social species. As a whole, we benefit from cooperation and altruism, but as individuals we can benefit from selfish behavior and take advantage of the social system. Like all social animals, we have evolved to detect cheaters and cowards who benefit from society without returning anything to it. Like other social animals, we are political, we form pecking orders and alliances. According to evolutionary psychology (http://www.psych.ucsb.edu/research/cep/primer.html), human intelligence has actually evolved to its high level, primarily to solve complex problems of politics and competition with each other.

One outcome of the evolution of behavior and mind is sexual politics, the development of behaviors that improve our chances of passing on our genes in a social context. One behavior that is almost universal in social animals is the impulse to prevent other individuals from breeding. This is not a conscious desire on our part, but we have certain impulses that encourage our genes to propagate more than others’. In particular, when we see or imagine other’s having sex, it is upsetting.

In Frans de Waal’s classic book, Chimpanzee Politics (http://www.press.jhu.edu/books/title_pages/1293.html), he describes this behavior a closely related species. In the image above, we see a dominant adult male punishing a younger male whom he caught attempting to mate with a female. The sight of other chimps having sex causes immediate rage in an adult chimpanzee, and this behavior leads to strong male chimps mating more often than their competitors.

As civilized human beings, we tend to interpret these type of feeling as “moral outrage”, although their origin is much more primitive and genetically selfish. To avoid the negative consequences of sexual politics, we’ve learned to keep sex private. We’ve agreed to monogamous marriage as a fair and equitable scheme to prevent what is seen in some primitive societies and religious cults: a sexual monopoly by a few strong males with multiple wives.

But we’ve also learned to make political opportunity from these instinctive responses. By publishing sexual gossip about a public figure — such as an affair or an unusual sexual orientation– mental images of the other person engaging in sexual activity are invoked; and thus, an instinctive feeling of anger or anxiety is stimulated.