Ian Kerner, a sexuality counselor and New York Times best-selling author, blogs about sex on Thursdays on The Chart. Read more from him on his website, GoodInBed.

What do female orgasms and male nipples have in common? It’s a question that is helping inform research into the purpose of female orgasm (other than simply as a form of pleasure).

Investigators want to know whether the female orgasm is an “adaptation” or “byproduct” of evolution. In other words, does the female orgasm, like the male orgasm, have its own evolutionary raison d’etre and contribute directly to reproductive success? Or is it just an awesome bonus? Make that totally awesome.

This question of whether the female orgasm is an adaptation or a byproduct came to the fore in 2005 with the publication of “The Case of the Female Orgasm: Bias in the Science of Evolution,” in which Indiana University professor Elisabeth Lloyd rigorously examined 21 theories that sought to promote