The belief that homosexuality is a choice is baseless!
Results from recent scientific research studies demonstrate that sexual orientation is fixed before birth and prenatal hormones and genetic factors play major roles in determining sexual orientation, disproving the belief that child rearing, social factors, and personal choices are responsible.
I will summarize major points from what I know about the recent research on homosexuality.
1. There is a significant body of new evidence that indicates that gender identity and sexual orientation are programmed during intrauterine (in the womb) fetal brain development as a result of genetic and hormonal factors. No research so far has been able to show evidence of the previously held belief that gender imprinting occurs during early age of 1-3 (in the well known case of David Reimer, this had led to tragic consequences!)
2. Although, the exact genes have not been determined, because sexual orientation is a complex phenotype, it likely involves actions of multiple genes. Increasing evidence indicate that women with gay sons have extreme skewing of X chromosome inactivation (a form of natural gene silencing), suggesting perhaps some of the genes are located on the X chromosome
3. One might argue that if genetic factors determine homosexuality and since it does not result in progeny (in most cases), why is it not selected against in nature in accordance with Darwinian theory of evolution and natural selection? Multiple recent studies looking at the maternal line of gay men found that female relatives have significantly higher fecundity (ability to reproduce) than the female relatives and ancestors of straight men. Therefore, it appears that this X-linked trait that may contribute to homosexuality also benefits the female carriers by increasing their fertility, allowing it to exist and thrive in nature. As a biologist myself, I find these results extremely interesting
During the intrauterine period, gender identity, sexual orientation and other behaviors are programmed in the brain in a sexually dimorphic way. The human fetal brain develops into the male direction through a direct action of testosterone and in the female direction through the absence of such an action. Sexual differentiation of the genitals takes place before the sexual differentiation of the brain. The degree of genital masculinization does thus not necessarily re?ect the degree of masculinization of the brain. Also, evidence for an effect of one's social environment after birth on the development of gender identity and sexual orientation is lacking.
Because sexual differentiation of the brain occurs at at different time during fetal development, why is it difficult to believe that in a small minority of cases, as a result of differential gene expression and hormonal effects, the brain develops differently giving rise to homosexual orientation.
In summary, homosexuality is inborn!
References:
The quoted text above is adapted from a very informative recent review article by a world-renowned neurobiologist Dr. Swaab:
A.-M. Bao, D.F. Swaab / Frontiers in Neuroendocrinology 32 (2011) 214–226.
And for the third point:
Camperio-Ciani, A., et al. (2004). Proceedings of the Royal Society of London, B 271, 2217-2224.
Camperio Ciani, A. (2009). Sexual Medicine, 6, 449-455.
Iemmola F., et al (2009). Arch Sex Behav. 38 (3), 393-9.
Rahman Q., et al (2008). Arch Sex Behav. 37 (6), 962-9.
Ciani AC, et al. (2009). J Sex Med. 6 (2), 449-55.
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