by : Simon LeVay and Dean H. Hamer
Two pieces of evidence, a structure within the human brain and a genetic link, point to a biological component for male homosexuality.
Most men are sexually attracted to women, most women to men. To many people, this seems only the natural order of things, the appropriate manifestation of biological instinct, reinforced by education, religion and the law. Yet a significant minority of men and women estimates range from 1 to 5 percent are attracted exclusively to members of their own sex. Many others are drawn, in varying degrees, to both men and women.
How are we to understand such diversity in sexual orientation? Does it derive from variations in our genes or our physiology, from the intricacies of our personal history or from some confluence of these? Is it for that matter a choice rather than a compulsion? Probably no one factor alone can elucidate so complex and variable a trait as sexual orientation. But recent laboratory studies, including our own, indicate that genes and brain development play a signifcant role. How, we do not yet know. It may be that genes influence the sexual differentiation of the brain and its interaction with the outside world, thus diversifying its already vast range of responses to sexual stimuli.
The search for biological roots of sexual orientation has run along two broad lines. The first draws on observations made in yet another hunt that for physical differences between men's and women's brains. As we shall see, 'gay' and 'straight' brains may be differentiated in curiously analogous fashion. The second approach is to scout out genes by studying the patterns in which homosexuality occurs in families and by directly examining the hereditary material, DNA.
Next : Part 2