Wednesday, August 16, 2006

Evolution and Sex

A new study found that men's sexual drive diminishes when they marry or otherwise settle into a permanent relationship, whereas women's sexual drive tends to remain constant. The researchers explained this as a result of evolutionary pressures: Men have an almost infinite number of sperm cells and their best strategy for reproduction is to mate with as many women as possible. When their environment doesn't contain large numbers of new women their sexual drive is reduced because frequent mating with the same woman, possibly already pregnant, is pointless. Women, on the other hand, have a limited number of eggs and the best strategy for them is to mate selectively with a good quality man and to remain faithful to him so that he will stay around to help with the children. A constant sex drive helps in this.

All this makes excellent evolutionary sense. Except that I made up the study. The real study results are the opposite:

Researchers from Germany found that four years into a relationship, less than half of 30-year-old women wanted regular sex.

Conversely, the team found a man's libido remained the same regardless of how long he had been in a relationship.

Writing in the journal Human Nature, the scientists said the differences resulted from how humans had evolved.


Dr Dietrich Klusmann, lead author of the study and a psychologist from Hamburg-Eppendorf University, believed the differences were down to human evolution.

He said: "For men, a good reason their sexual motivation to remain constant would be to guard against being cuckolded by another male."

But women, he said, have evolved to have a high sex drive when they are initially in a relationship in order to form a "pair bond" with their partner.

But, once this bond is sealed a woman's sexual appetite declines, he added.

He said animal behaviour studies suggest this could be because females may be diverting their sexual interest towards other men, in order to secure the best combinations of genetic material for their offspring.

Or, he said, this could be because limiting sex may boost their partner's interest in it.

Sorry if you feel that I cheated you. But this is a real problem in studies using evolutionary psychology. Any finding can be justified by making up a story about why it would be optimal. At the same time, there is nothing about the possibility that the data itself might be flawed. The data is based on answers by men and women, after all. Maybe men feel obliged to ignore any decreases in their sex drives? Maybe women are almost encouraged in belittling their sexual drives? Or it could be the definition of "is" the way Bill Clinton used it. Maybe sexuality means something different for men and women.

Thanks to bikinikiller.