No formal proof but numerous arguments

Finally, a last known factor at this stage contributes to the explanation of masculine homosexuality: the number of older brothers born of the same mother. “The more male children a woman has, the greater the probability that boys born later will be homosexual”, states Jacques Balthazart. “This probability increases by 33% for each boy born of the same mother. This was demonstrated by Canadian researchers. Here too, it had been suggested that it was a question of family environment, but the data accumulated from 25,000 homosexual males made it possible to discount this argument”. The most probable hypothesis which could explain this effect of older brothers is that the mother develops antibodies against a protein produced by the male foetuses. These antibodies modify the development and therefore the structure of these babies. “And the effect of these antibodies increases with each successive male embryo”, continues the researcher.

In conclusion, several studies show a hormonal, genetic and epigenetic influence on sexual orientation. None of them can alone offer a complete explanation for homosexuality and each explanation in isolation can be disproved. “But when we look at all these studies, they constitute an array of arguments which suggest that biology has a great influence on sexual orientation and therefore homosexuality”, affirms Jacques Balthazart. “It would be difficult to imagine that, from an evolutionary point of view, sexual orientation, which is crucial for the survival of the species, could go from being controlled  by biological factors in animals, to being merely determined by education in humans”, he continues. “In addition, homosexuality is present in all human societies with more or less the same frequency. The more tolerant a society is with regard to homosexuality does not lead to an increase in homosexual individuals”.

In the face of arguments suggesting the influence of biology on sexual orientation, there are two types of reactions as Jacques Balthazart was able to experience. “For some people, it is a relief to be able to explain their sexual orientation from a biological point of view. This deculpabilises the parents or individual concerned with regard to the situation. Homosexuality is often more readily accepted when biology is seen to have a role in this sexual orientation”, explains the scientist. Other people, however, do not want to entertain any biological explanation. “This is either because they prefer to assume that it is a deliberate choice, or because it is a problem for them that a medical approach is taken towards the phenomenon”. The question of the origin of homosexuality is a complex and sensitive one. Scientific progress makes it possible to provide some answers but has not yet provided formal proof of a biological origin. And if this proof is obtained one day, will it put an end to the many debates surrounding homosexuality? Nothing could be less certain…