Books "Biology of homosexuality " is a rather bold title , right?
Jacques Balthazart For the French public yes, and that is precisely what I intended audience . Because the Anglo -Saxons are much more knowledgeable in this regard. Not only found among them many opponents to the idea of a biological component to homosexuality. But opinions are divided , there is debate , whereas in France and in the Latin countries , this is anathema.
Most books published in French until recently have homosexuality as the result of an upset child , a particular environment , or a choice, erase or deny the scientific data available . I said that what interests me is not homosexuality as such , but to understand how a fairly sophisticated behavioral characteristic may possibly be determined by biological factors . I am asking just as many questions about my heterosexuality as homosexuality.
But you work on the animal?==>
Yes, I studied for over thirty-five hormonal and neural mechanisms that control the so-called instinctive behaviors . I worked particularly on the differences between males and females. Gender disparities are largely the result of hormones during embryonic or early stages of development after birth. Including behaviorally . This has been known for half a century : the sex hormones in the perinatal period , an organizer effect , they alter the structure of the brain and its connections. Regarding sexual behavior were identified specific sites deep brain whose role is decisive. And implantation of testosterone in the preoptic area of adult castrated male is sufficient to restore an active sexual behavior.
The brain can be regarded as a sexual organ ?
It should be understood that the action of sex hormones early in life is irreversible. It is associated with a critical period : the organizer effect can only occur in a very specific time window corresponding to a stage of development of the nervous system.
In the male, human or animal , the organizers effects of testosterone are called " indirect genetic ." There on the Y chromosome a gene, SRY, which induces the formation of the testes. They produce testosterone during embryonic life and it is this hormone which will produce male characteristics , both morphological (penis and scrotum) and behavioral .
In the absence of testosterone or testosterone receptors , this results in behavioral patterns and female genital , even if the individual is genetically male. For ten years, we think there is further direct genetic effects , which act independently of testosterone , but the subject is still in the research stage .
What relationship is there between a sex determination and homosexuality ?
We realized in the last ten years, these hormonal mechanisms of differentiation also affect mate choice in animals. We know making male rats and ferrets become homosexual or bisexual homosexual tendency . Or by manipulating the hormonal conditions in the perinatal life either manipulating the preoptic area in adulthood .
What evidence do we have that this hormonal determinism also exist in humans ?
First there was a substantive argument , which is the evolutionary continuity of species . The preoptic area exists in humans as in all mammals , birds, reptiles , amphibians and fish. Recovery of sexual behavior in male castrated him by implanting testosterone in this area was performed in all species of birds and mammals that have been studied. In all tetrapods , including humans part , the preoptic area is extremely similar and contains the same neurons producing the same neurotransmitters and connected to the same areas of the brain .
Will it more concrete arguments?
There are many . To begin , we see in our species a series of genetic and hormonal accidents which can learn from. The problem is best studied congenital adrenal hyperplasia ( CAH ) . Because of a mutated gene , cortisol production is interrupted and the adrenal glands begin to produce steroids that have androgenic action. This leads to the birth of girls with genital more or less masculinized structures.
There is even that one can not distinguish small boys at birth, but now they are always detected . If their genital structures are considered too ambivalent , are corrected by surgery and to avoid serious metabolic problems , they must take cortisol lifetime.
But when these girls grow up, we see that they are on average much more aggressive than others, prefer football games with dolls . These are tomboys . Later they frequently choose careers typically associated with men (engineers , etc.). . And an increased incidence of homosexuality is observed in them. Between 15-20 % and 35% , according to studies , while the usual rate of female homosexuality is less than 15%.
This is a clue, but that does not make a big difference ...
No, and in fact the discussion is lively . We could evoke a reluctance to engage in heterosexual relationships due to a devaluation of self-image and relationships with penetration difficulties because genital structures corrected by surgery would not be optimal.
But the idea of prenatal influence of testosterone is supported by an observation: the incidence of homosexual orientation is correlated with the severity of hormonal problem . The disease is more serious , the greater the impact is great . What can be objected that this is a posteriori studies . It is not controlled experiments .
In summary , it seems difficult to deny that there is a hormonal effect , but it is not sufficient to explain sexual orientation. This is normal . In any study linking the biological behavior , there is a significant variance , indicating that the factor of interest is not the only cause . It only helps to explain part of the phenomenon. It is difficult to convey to a wider public, who prefer it to be black or white concept . In fact, any disease in humans completely opposite sexual orientation.
What other types of index available?
We observed in homosexual populations of sexually differentiated known as characters, animal , they grow under the influence of embryonic testosterone. My favorite example is called otoacoustic emissions ( OAE ) .
It was found that the inner ear, in addition to his hearing , emits sounds as barely audible clicks . But women from childhood , are producing more than men and greater amplitude. This is also true of females in other mammals . It is believed that low EOA males is the result of exposure to androgens during fetal life and this was clearly demonstrated in various animal species .
Strong evidence comes from studies on the hyena . In this species , females are highly masculinized by androgens in utero and immediately after birth , so that their genital structures are similar to those of the first male view. The clitoris is so bloated that it takes for a penis. And in this case, the amplitude of the EOA is not greater in females than in males, it is even slightly lower .
Furthermore , if a pregnant mother is treated with antiandrogens, have a smaller amplitude than normal EOA . The same result was observed in sheep. But it was found that lesbians and bisexual women have masculinized EOA , suggesting that they were exposed to abnormally high levels of testosterone during embryonic life . This is also the case for women who lived in utero with a twin brother and were therefore potentially exposed to a slightly higher testosterone levels.
Apart from these hormonal effects , can we invoke a hereditary component of homosexuality ?
It is indeed another class of indices. I mentioned earlier the possibility of direct genetic effects. It is clear , indisputable , that homosexuality is partly transmitted . Studies of twins indicate a high heritability of the variance in sexual orientation, 30% to 60%. We also know that a gay man is more likely to have gay men among his ancestors on the maternal side . This suggests transmission by matriarchal . Three independent studies indicate the existence of a connection between the transmission of male homosexuality and markers on a very specific region of the X chromosome
Brain differences often mentioned among heterosexual and homosexual human brain have they proved ?
The problem is that the studies are very difficult to achieve. Differences , for example in the preoptic area , structures involve too small to be seen by medical imaging . But their smallness tells us nothing of their functionality. To give an idea, a core 1 mm3 can contain 10,000 neurons, which may each thousand connections , giving ten million connections. This allows for a sense of great complexity circuit.
I conclude that the studies carried out are probably statistically significant differences in neuronal density or volume of certain nuclei. But again , what we find is a difference in the average. There recoveries . This is one explanation , nothing more.
Finally, all these data provide only indices statistical nature ?
It is undeniable, but abutted they form a body of evidence in favor of a strong biological influence. What is its real significance ? She explains 50% of the variance ? 80 % ? To date , no one can say. But the challenge falls denial.
If the biological component is strong, how can we explain the point of view of the theory of evolution?
There are several hypotheses. The real issue is the exclusive homosexuality. How to explain that evolution, which aims to maximize reproduction, has enabled its emergence and persistence ? We must first note that it is not proper to man . There is at least one species in which it is so undisputed : Rocky Mountain sheep . We see that go with a ram force , ignoring the sheep heat side. It must be admitted that there is a hidden benefit associated .
The most popular hypothesis is that of hypersexuality women matched . A recent study shows that mothers , grandmothers , aunts or cousins gay men have more children than heterosexuals. Another hypothesis is that homosexuals in the difficult conditions of our evolutionary history , helped their relatives to ensure the survival of their children. In both cases , the selection favors genes that predispose to homosexuality.
Will he still arguments to suggest that homosexuality is a cultural construct ?
The most common theory is psychoanalysis , where homosexuality is , for simplicity, the result of an unresolved Oedipus complex . There are also constructivists , for whom sexual orientation results from environmental influences .
These theories face two main problems. The first is that there is no quantitative studies showing a relationship between the psychological history of the child or the environment in which he was raised and subsequent sexual orientation category. The second , by contrast , is the amount of examples showing the absence of such influence. We often speak of the absent father . But there are millions of single mothers and no father did not induce any increase in the incidence of homosexuality.
There are also traditional societies , Malaysia and Micronesia for example, where homosexual relations are imposed on teenagers before marriage. Again, we do not see any particular incidence of homosexuality in adulthood . No more than boys who had homosexual practices during adolescence time when the school was not mixed . In fact , the frequency of homosexuality is almost constant in all societies and, as far as can be judged , at all times .
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