同性恋进化之谜_BEC初级作文_BEC初级-查字典英语网

同性恋进化之谜

Similarly in the West, there is evidence that many people go through a phase of homosexual activity. In the 1940s, US sex researcher Alfred Kinsey found that while just 4% of white men were exclusively gay after adolescence, 10% had a three-year period of gay activity and 37% had gay sex at some point in their lives.

A national survey of sexual attitudes in the UK last yearcame up with lower figures. Some 16% of women said they had had a sexual experience with another woman (8% had genital contact), and 7% of men said they had had a sexual experience with a man (with 5% having genital contact).

But most scientists researching gay evolution are interested in an ongoing, internal pattern of desire rather than whether people identify as gay or straight or how often people have gay sex. "Sexual identity and sexual behaviours are not good measures of sexual orientation," says Paul Vasey. "Sexual feelings are."

Qazi Rahman says that alleles coding for same sex attraction only explain some of the variety in human sexuality. Other, naturally varying biological factors come into play, with about one in seven gay men, he says, owing their sexuality to the "big brother effect".

This has nothing to do with George Orwell, but describes the observation that boys with older brothers are significantly more likely to become gay - with every older brother the chance of homosexuality increases by about a third. No-one knows why this is, but one theory is that with each male pregnancy, a woman's body forms an immune reaction to proteins that have a role in the development of the male brain. Since this only comes into play after several siblings have been born - most of whom are heterosexual and go on to have children - this pre-natal quirk hasn't been selected away by evolution.