Sexual attraction of individuals of the same sex have always been a difficult riddle to solve may have tried to explain this seemingly reoccurring phenomena in many mammals .Levay is best known for his research on the brain and sexuality explores the reasons for different sexual orientations. According to the inversion hypothesis he asserts that sexual orientation is an inborn reversal of gender trait; this is where male or female inverts to certain extend and is inclined to traditionally pursuits of the different gender. In his studies he studied the neuroanatomic differences between homosexual and heterosexual men. In his study he found the INAH3 which is the third interstitial nucleus of the anterior hypothalamus was two to three times larger in heterosexual men than in gay men. This is to show that one’s orientation is controlled mainly by biological factors other factors include gene and parental traits. However he cautioned against the use of his study to validate the claim that homosexuality is inborn.
In his study he found there were differences in NAH3 of size between heterosexual and homosexual men many of which had AIDS. Even studies show that male rats an other mammals may develop as females when exposed to prenatal that are before they are born or post natal stress or both. Stress inhibits sex hormones such as testicular hormones and in particular testosterone which is responsible for the male characteristics. The males that were exposed to stress showed low levels of copulatory behavior and weirdly high rates of feminine behaviors. to explain this behavior on has to understand that hormones control the sexual behaviors.
They activate and stimulate the neural circuits which trigger the sex specific behavior and stimuli.Testosterone induces male like behaviors especially physical traits and without this hormone estrogen sets in and its causes the female like development. Although all sexes produce both male and female hormones they always differ by a huge margin. For example during prenatal the two hormones determine whether the fetus develops a testis or mammary glands.
The gay hypothesis was supported by the fact that In the course of Levay’s study he concluded that there was significant psychological and cognitive difference between gay and straight people. Gay men on average have slightly longer and thicker penis. Also Gay men and lesbians were found to be more verbally fluent than non gays of the same sex. Further cognitive difference is shown by gay men exhibited higher scores that non gay men on tests of objet location memory. These findings also fit well with model suggested by Hirschfeld much much earlier and this in his views adds strength to the notion that development of sexual orientations at least in human beings is closely related to the prenatal sexual differentiation of the brain.
According to an article in wikipaedia difference was that gay men and straight wome had equally proportioned brain hemispheres but the opposite of the had a slightly larger brain hemispheres. The VIP SCN nucleus of the hypothalamus is larger in men than in women and larger in gay men than in heterosexual men. It is also purported that the anterior commissure is larger in women than men and was reported to be larger in gay men than in non-gay men, but a subsequent study disapproved this.Also Gay men's brains respond differently to fluoxetine, a selective serotonin reuptake inhibitor.
Never the less this study may be question on the ground that many of his subjects for research were AIDS patient and may have had other physiological and pathogenic conditions. It therefore does not conclusively conclude the large brain is as a result of their being homosexual. Some people have also suggested that homosexual or heterosexual activity may have influenced the size of particularly bodily structures rather that the vice versa. The study conducted also did not take into consideration the social economic factors of the subjects of the study. I would have expected the study to be done to people of similar backgrounds who live in a controlled environment. Physiological factors are hugely influenced by what we do according to evolution and not the other way round some may argue. This study was also conducted on people who had already been sexually.