Monday, May 09, 2005

Homosexuality: More Biology Than Choice?

An interesting new study will be released tomorrow by the Proceedings of the Natural Academy of Sciences showing that homosexual men respond to male odor the same as straight women. The study was conducted by Dr. Ivanka Savic and colleagues in Stockholm, Sweden. Here's the science behind it from the NYTs.
Most odors cause specific, smell-related regions of the human brain to light up when visualized by a PET scanner, a form of brain imaging that tracks blood flow in the brain and hence, by inference, the presence of suddenly active neurons in need of extra glucose. Several years ago, Dr. Savic and colleagues showed that the two chemicals activated the brain in a quite different way from ordinary scents. The estrogen-like compound, though it activated the usual smell-related regions in women, lit up the hypothalamus in men. This is a brain center that governs sexual behavior and, through its control of the pituitary gland lying just beneath it, the hormonal state of the body.

The male sweat chemical, on the other hand, did just the opposite; it activated mostly the hypothalamus in women and the smell-related regions in men. The two chemicals seemed to be leading a double life, playing the role of odor with one sex and of pheromone with another.

Dr. Savic has now repeated the experiment but with the addition of homosexual men as a third group. The gay men responded to the two chemicals in the same way as did women, she reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.
While this study matters scientifically because it may show humans produce phermones that help attract mates, it matters culturally as well. It seems that science is a step closer to proving homosexuality is disproportionately genetic.
Dr. [Simon] LeVay said he believed from animal experiments that the size differences in the hypothalamic region he had studied arose before birth, perhaps in response to differences in the circulating level of sex hormones. Both his finding and Dr. Savic's suggest the hypothalamus is specifically organized in relation to sexual orientation, he said.

Some researchers believe there is likely to be a genetic component of homosexuality because of its concordance among twins. The occurrence of male homosexuality in both members of a twin pair is 22 percent in non-identical twins but rises to 52 percent in identical twins. On the other hand, gay men have fewer children, meaning that in Darwinian terms any genetic variant that promotes homosexuality should be quickly eliminated from the population. Dr. [Dean]Hamer [a geneticist at the National Institutes of Health] believes such genes may nevertheless persist because, although they reduce descendants in gay men, they increase fertility in women.
And for those fundamentalist bigots that like to carry "God hates fags" signs and who will continue to cling to their despicable prejudice despite the evidence, I have only one question, "What loving God creates creatures in his image that have a sexual predilection that earns them eternal hellfire?"