Sperm Compete (duh)

Here's a recent press release, from Blackwell, about an article (behind firewall) in the February issue of Current Directions in Psychological Science. Not only are they three months late on getting out this "news," but please note the writer's egregious oversimplification of the work (in bold). Sigh. (The news is actually much, much older than than three months. Robin Baker et al. have been observing sperm competition in all kinds of animals, including humans, for, oh I dunno, 20+ years...still, glad to see it making headlines again.)

Research suggests men's sexual behavior adapts to perceived threats

Behavioral and physical characteristics allow men to compete in fertilization

Davie, Fla. May 08, 2007 -- A review of the latest research in sexual adaptation shows that evidence is building for what researchers call "sperm competition." According to a review appearing in Current Directions in Psychological Science, physical and behavioral sexual characteristics exhibited by human males indicate that males have evolved to deliver their sperm more effectively to females with multiple partners.

"Although many people are familiar with the idea of animals competing for mates before sex occurs, through mating displays such as bright feathers or butting antlers, we are finding more evidence that there is also competition after mating occurs," says author Todd K. Shackelford. "An alternative way of thinking about it is that there is not only competition between males for mates, but competition between males for fertilization."

The research presented in the review covers physical adaptations, including penis shape and style of intercourse, as well as behavior in response to perceived infidelity that all serve to increase the success of fertilization. "The studies have shown that when partners are separated for periods of time, males are more likely to arouse easily, produce more sperm, and even rape their partners," says Shackelford. According to Shackelford and co-author Aaron T. Goetz, this does not mean that women are promiscuous by nature, but it is evidence that humans are not naturally a monogamous species.

Shackelford is quick to point out, however, that females are not passive partners in the sexual relationship. "Although this review focused on male adaptations, sexual conflict between males and females produces a co-evolutionary arms race between the sexes, in which an advantage gained by one sex selects for counter-adaptations in the other sex."