Third, several scientists think that sexual orientation and sex characteristics are determined at different step in development of the embryo and something may happen during pregnancy that will switch differently these two phases
Indications are that sex orientation in humans depends critically upon the hormone balance prevailing during the third and fourth months of pregnancy, while secondary sex characteristics and sex-typical behaviour patterns are influenced more by hormones circulating during the fifth and sixth months of pregnancy. If the hormone balance changes from one phase of foetal development to the next, inconsistencies between sexual orientation and sex-role behaviour may be observed. Sex orientation is fixed relatively early in the old 'limbic' part of the brain, whereas sex-role behaviours are laid down later on in pregnancy in more diverse, 'newer' parts of the brain.
Research shows the brains of homosexuals are structurally different from heterosexuals, which could suggest that the homosexual tendency is imprinted in the brain from birth. So it is not necessarily a psychological condition, nor a religious one. Since homosexually has been around since...well..homo sapiens, this makes more since with the real world as well.
Simon LeVay observed that INAH3 was more than twice as large in the men as in the women. But INAH3 was also between two and three fumes larger in the straight men than in the gay men. In some gay men, as in the example shown at the top of the opposite page, the cell group was altogether absent. Statistical analysis indicated that the probability of this result's being attributed to chance was about one in 1,000. In fact, there was no significant difference between volumes of INAH3 in the gay men and in the women. So the investigation suggested a dimorphism related to male sexual orientation about as great as that related to sex.
One other feature in brains that is related to sexual orientation has been reported by Allen and Gorski. They found that the anterior commissure, a bundle of fibers running across the midline of the brain, is smallest in heterosexual men, larger in women and largest in gay men. After correcting for overall brain size, the anterior commissure in women and in gay men were comparable in size.
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Fourth, and somehow related with third, homosexual behaviour is also observed in the animal kingdom.