Born that way

Picked up in Smith's Alternative Bookshop Born Gay: The Psychobiology of Sex Orientation which is a highly readable summary of current scientific research on the origins of sexual orientation.

The book takes the lay reader gently through the results of a lot of scientific studies. I particularly enjoyed the debunking of Freudian analysis (pp30ff). The authors also point out that a major limitation on inference from animal behaviour is that sexual monogamy is an unusual mating strategy among species (pp62-3).

Identifying sexual orientation is a complex matter, given there are self-labelling, behaviour, feelings and physiological responses available as identifiers. The evidence based on feelings suggests that about 2-3.5% of men and 0.5-1.5% of women are gay (p.22) while physiological response evidence does not support the existence of male bisexuality (pp 21-22).

Basically, the research shows that (pp 145-6):

sexual orientation is stable (showing much the same level of incidence across cultures) and bimodal (if male bisexuality exists, it is rare);
there is no scientific backing for sexual orientation being influenced by social factors such as upbringing, contagion or seduction;
there is evidence for genetic influence, but it accounts for less than half of sexual variance and seems to be spread across several genes;
the most likely reason for the survival of said genes is selection decisions by the other sex;
prenatal sex hormones are implicated in the origins of sexual orientation;
this is further supported by the clear existence of a fraternal birth order affect (each older brother raises a son's chance of being gay by about a third accounting for about one-in-seven gay men);
the brains of gay men and women seem to be cross-sex shifted in certain respects (i.e. more like those of women and men respectively);
sexual orientation can be predicted early in life from play patterns and toy preference;
the existence of sub-types of homosexuals differentiated by hormones is doubtful.

An amusing result is that gay men seem to tend to have larger penises than straight men—being about 5% longer on average (pp84-85). Gay men are about about a third more likely to be not right-handed, gay women about 90% more likely to be not right-handed, than straights (p.124).

Homosexuality is an uncommon (about one-in-30 men and one-in-70 women) but persistent human variation. It is neither unnatural nor contagious. The real issue is not the existence of human variance, but whether folk can cope with difference—persecution of homosexuals is just a large majority monstrously bullying a small and vulnerable minority. But coping with difference is a problem that extends way beyond sexual variation.