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Sexual orientation in all its aspects
4/13/16

When the hormonal balance is upset by illness

In humans, this difference in the size of the sexually dimorphic nucleus had already been observed as far back as 1993. “This is old information but still remains relatively unknown, especially in France where the influence of biology on homosexuality is rarely spoken about”, the Professor continues, “This area of the brain was histologically examined in humans based on examination of the brains of individuals who died from the AIDS epidemic. But observation of this difference does not constitute formal proof because it is difficult to be sure about an individual’s sexual orientation before their death and some say that the reduced size of the sexually dimorphic nucleus is a consequence and not a cause of homosexuality”. In rats and sheep, scientists have proved that it is a consequence of the action of prenatal hormones and that the size of this nucleus is correlated to the sexual orientation of these animals. It is therefore tempting to think that the same mechanisms could apply in humans…  

Other arguments about the influence of embryonic hormones on human sexual orientation can be added to the list. There are illnesses which affect the embryonic hormonal balance which are associated with a change in sexual orientation. For example, hyperplasia of the adrenal glands consists of an abnormal development of these glands which then no longer secrete cortisol but which produce androgens instead. “The girls affected are often exposed to much higher levels of male hormones than normal during the course of their embryonic life. This results in a masculinisation of genital structures. Some are born with a fusion of the lips or a clitoris the size of a penis etc.”, explains Jacques Balthazart. Very often, these anomalies are corrected at birth and the children in question are raised as little girls. But, in terms of behaviour, they are more inclined to play at more masculine games, and, at an adult age, the incidence of female homosexuality in these in these young girls is in the order of 20% to 40% according to studies. “It could therefore be thought that this excess of androgens during prenatal life leads to a masculinisation of sexual preferences”, continues the scientist.  “And the higher the levels of secretion of prenatal androgens, the more homosexuality incidence increases. It is one of the arguments for the influence of hormones on sexual orientation in humans”.

Finally, an entire series of human characteristics are influenced by prenatal hormones and can be correlated to the sexual orientation of individuals. A series of factors are masculinised by prenatal testosterone. The relative length of the 2nd and 4th fingers of the right hand, for example. “Men generally have a shorter 2nd finger than the 4th”, explains Jacques Balthazart. “And homosexual women also statistically have a shorter 2nd finger than the 4th which would suggest that they have been exposed to an excess of testosterone. Of course this does not work on an individual level but it has been statistically confirmed”.

FIG2 Sexual orientation

Unfortunately, it is very complicated to obtain formal proof of the influence of embryonic hormones on sexual orientation. In fact, there is an enormous amount of variation because hormonal disturbances can occur at different stages of embryonic life. This proof could eventually be obtained thanks to a study of individuals from the embryonic stage up to the age of 25. “In an ideal world, it would be necessary to take blood samples from embryos and observe the sexual orientation these individuals have at an adult age. This is both ethically unacceptable and nobody has the means to conduct such a study”, states the scientist.

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