Why Women have Sex: UnderStanding SexUal motivation, From adventUre to revenge (and everything in BetWeen) by Cindy Meston and David Buss (The Bodley Head, [pounds sterling]12.99)
Why men Want Sex & Women need love by Allan & Barbara Pease (Orion, [pounds sterling]12.99)
IT'S not easy to read two volumes of evolutionary psychology on the Tube without blushing. On the plus side, friends have never found me so interesting. Mention that there are 237 reasons women have sex and the room grows strangely quiet.
We know we find some faces and bodies "hot" but remain largely unaware of the hidden adaptive logic behind our desires. It's a sad fact that much of our modern, liberated behaviour comes down to ancient sexual psychology.
Trim waists, big breasts, V-shaped torsos -- we're biologically "wired" to look for partners with genetic and resource benefits, even if we have no intention of marrying. The wealthier a man, the more frequently his partner orgasms. I can't go for a meal now without knowing that it's all part of the exchange of meat for sex.
Why Women Have Sex is billed as the new Kinsey Report. Meston, a professor of clinical psychology at the University of Texas at Austin, directs the Sexual Psychophysiology Laboratory. Buss, an expert on strategies of human mating, is author of The Evolution of Desire.
They draw on 1,006 interviews with women aged 18-86, as well as the latest research on the physiology underlying arousal (everything from monitoring genital blood flow to studying women in singles bars).
Refreshingly, they blow out of the water the theory that women only have sex to procreate. Women's 237 "rea-sonsrange from sex as a defence against infidelity to boosting self-confidence, as barter for gifts or housework and as a cure for a migraine. And yes, pleasure too -- in our evolutionary past, orgasms were a "lure" to improve our chances of pregnancy.
But women can be Machiavellian.
Meston and Buss find evidence of "mate poaching" and "jealousy evocation" tactics ("I decided to have sex with him to make my partner realise that other people wanted me").
My favourite reason is when Mr Acceptable Enough becomes Mr Can't Live Without. After having repeated sex, we form a conditioned association. Pretty soon just seeing him floods our brain with oxytocin, the cuddle hormone. …