The female orgasm has been a topic of debate among evolutionary biologists (and among many other people as well, of course). Is it adaptive, or a by-product of the male orgasm? Does it suck sperm into the uterus, or strengthens the pair bond? Or did it ‘tag along’ with the development of the male orgasm?

A new study, published in Animal Behaviour, takes a look at the question. The authors argue that, if the female orgasm is an evolutionary by-product, similar genes would lie at the root of orgasmic function in both sexes. Consequentially, opposite-sex twins and siblings would share more similarities in their susceptibility to orgasm.

The researchers quizzed over 10,000 people, including identical and non-identical twins and regular siblings. Same-sex identical twins appeared to be more similar in orgasmic function than non-identical twins, suggesting that genes play a role. But they also found that opposite-sex twins and siblings had no correlation in ‘orgasmability’, as the researchers called it. This indicates that the male and female orgasm have evolved through different routes, rendering the by-product hypothesis incorrect.

Now, does this settle it? Not entirely. The study does provide some data that decreases the viability of the by-product hypothesis, but to make a stronger case, identification of the genes in question would certainly help. So, for now, it seems that the evolutionary mystery of the female orgasm is not yet completely resolved…

(Source: The Mad Hatters)

The authors write:

This suggests that different genetic factors underlie male and female orgasmic function and that selection pressures on male orgasmic function do not act substantively on female orgasmic function. These results challenge the by-product theory of female orgasm.

For a critical review of the paper, check Pharyngula here. Some valid points are made. In particular, the study is based on self-reporting, and is thus subjected to all the issues that come with that. Furthermore, men and women were given a different set of question, which obviously makes it hard to compare the answers of both sexes.

Reference

Zietsch, B.P. and Santtila, P. (2011). Genetic analysis of orgasmic function in twins and siblings does not support the by-product theory of the female orgasm. Animal Behaviour. Available online 3 September 2011. doi:10.1016/anbehav.2011.08.002.