from Le Nouvel Observateur
28-12-2103
translation doxa-louise
IS HOMOSEXUALITY OF BIOLOGICAL ORIGIN?
According to Belgian researcher Jacques Balthazart, one does not become homosexual, one is born that way. Interview.
Most available works in French on the subject of homosexuality present it as the
result of a certain childhood or environment, indeed a choice, and this going against
scientific givens. All books except one, that of Jacques Balthazart, head of neuroendocrinology
of behaviour at university Liège. His view is that homosexuality has an important biological aspect.
Our brethren from ‘BoOks’ met with him. Also to be readin their December issue.
BoOks ‘Biologie de l’homosexualité’ is a provoctive title, is it not?
Jacques Balthazart For a French public, it is, and it is this audience that I am aiming for. Because
Anglo-Saxons are much more knowledgeable on this question. Not that there is not among them
opposition to the idea of a biological basis to homosexuality. But there is a diversity of opinion, there
is a debate whereas in France, in latin countries, it is a forbidden subject.
Most books in French present homosexuality as the result of a disrupted childhood, a particualr
environment, or a choice, and gloss over or deny much scientific evidence. I wish to make clear
that what is of interest to me, is not the promotion of homosexuality as such, but to attain an
understanding of how a behavioural component finally rather sophisticated can eventually be
accounted for by biological factors. I am thus raising as many questions about my own
heterosexuality as about homosexuality.
Yet you do a lot of work on animals?
Yes, I have been studying for thirty-five years the hormonal and nervous mechanisms that underly
so-called instinctive behaviours. I am particularly interested in differences between males and
females. Sexual differences are in great measure the result of the differing effects of hormones
during embryonic life or the first stages of development after birth. including on behaviour. We have
known this for a half-century: sexual hormones, during the perinatal stage, play an orgainzing role; t
hey modify brain organization and connections. With respect to sexual behaviours, we have identified
quite precise sites in the deep brain whose role is crucial. Thus the injection of testosterone in the
preoptical region of a castrated adult male will lead to the resumtion of active sexual behaviour.
Is the brain thus a sexual organ?
One needs to appreciate that the action of sexual hormones early in life is irreversible.
It is associated with a critical period: this orgainzing effect can only occur in a precise time window
correspondong to a certain stage in the developement of the nervous system.
For the male, animal or human, the organizing effects of testosterone are said to be
‘genetic indirect’. There is on the Y chromosome a gene, SRY, which leads to the formation of
testicules. These produce testosterone during embryonic life and it is this hormone that is
responsoble for masculin characterisitcs, morphological (penis and scrotum) as well as behavioural.
The abscence of testosterone or testosterone receptors will give female genital structures and
behaviours, even if the individual is genetically male. For the last ten years, we have come to think
there may be direct genetic effects, which act independently of testosterone; but the subject is still at
the research stage.
What is the relationship between sexual diffrentiation and homosexuality?
We have come to realize, in the last ten years, that hormonal mechanisms also determine
the choice of sexual partners. We know how to produce male rats or weasels who become
homosexual or bisexual with homosexual tendency. Either by manipulating hormonal conditions
during perinatal life, or by manipulating the preoptical region at adult life.
What tells us that such hormonal determinism might be the case for man?
There is first of all a basic argument, due to the evolutionary continuity of species.
There is a preoptical region in man as with all mammals, birds, reptiles, amphibians and fish.The
resumption of sexual behaviour in the castrated male has been achieved with all species of birds
and mammals that have been tested. For all tetrapods, of whom man is a member, this preoptical
region is quite similar; it contains the same neurons producing the identical neurotransmitters and
connected to the same areas of the brain.
The fact that we can manipulate sexual orientation in animals of our family, the mammals, by
intervening on the preoptical region, is a key argument, because sexual orientation is a diffrentiated
sexual characteristic that is crucial to the reproductive success of a species. I have trouble imagining,
as many would have it, that in the evolution of the human line this control could have been lost to
education, much more fragile and random. Not even to the mastery of the cortex, certainly much more
developed in man but which has never taken control of our most instinctive behaviours.
Are there more concrete arguments?
There are many. To begin with, there are in our species a number of genetic and hormonal accidents
from which we can learn. The most studied would be congenital adrenal hyperplasia(HCS). As a result
of a mutated gene, the production of cortisol is interrupted and the adrenal glands produce stereoids,
which have an androgenic effect. This leads to the birth of girls with more or less masculine genital structures.
There are even some one cannot distinguish from boys at birth, but today they are always detected. If their genital structures are deemed too ambivalent, they are corrected through surgery, and to avoid grave metabolic
problems, they will take cortisol their whole lives.
Indeed, when these little girls grow up, we see they engage in games that are much more aggressive
than that of others, that they prefer football to dolls. They are tomboys. As adults, they often choose professional careers normally associated with men (engineer and so on). and we find in this population, an increase in the incidence of homosexuality. Between 15-20% and 35%, depending on the studies, while the habitual
rate of female homosexuality is less than 15%.
It’s a clue but it doesn’t make that big a difference...
No, and effectively discussion here is lively. Have been evoqued a reluctance to engage in a heterosexual relationship, because of a devalorisation in self-image and because of the difficulties of relations with penetration where surgically altered genitals might not be optimal.
But the argument starting with a prenatal influence of testosterone is reinforced by a
finding: the incident rate of homosexuality is correlated with the severity of the hormonal problem. The more the illness is serious, the greater the incidence. To this one might well object that one is dealing with a posteriori studies. These are not controlled experiments.
To sum up, it seems to me difficult to deny that there is a hormonal incidence, but this is not sufficient to explain sexual orientation. It is habitual. As with all studies linking the biological with the behavioural, one should note an important variance, because the studied factor is not the sole cause. It explains only part of the phenomenon. It is a notion difficult to convey to the public at large, which prefers that questions be black or white. In point of fact, no illness in man completely alters sexual orientation.
What other kinds of clues might we have?
We have observed in homosexual populations sexually differentiated characteristics which we know, in animals, develop as a function of embryonic testosterone. My favourite example would be otoaccoustic emissions(EOA).
We have discovered that the inner ear, other than its auditory function, emits clicking sounds that are barely audible. Women, starting in infancy, produce more of these than men, and in greater quantity. It is also true of females in other species. We believe that the weakness of EOAs in males is the result of being exposed to androgens during foetal life and this has been clearly shown in other animal species.
A telling example is that of the hyena. In this species, the females are strongly
masculinized by androgens in utero and immediately after birth, to the point where their genital structures resemble those of the male. The clitoris is so hypertrophied it looks like a penis. And, in this species, the amplitude of EOAs is no greater in females than in males; it is even slightly inferior.
Further, if a mother in gestation is treated with antiandrogens, the childfen will present a frequency of EOAs superior to notmal. The same result is evident with sheep. And thus we have found that lesbian or bisexual women have masculine levels of EOAs, which would suggest that they were exposed to abnormal high levels of testosterones during embryonic life. It is equally the case with women who have lived in utero with a male twin and were thus potenitally exposed to a higher level of testosterone.
Independently of these hormonal effects, does it make sense to invoque an hereditary aspect to homosexuality?
Indeed there is another category of clues. I invoqued earlier the possibility of direct genetic effects. It is clear, without doubt, that homosexuality is partly transmitted. Studies on real twins reveal a strong inherited character to sexual orinetation, in the order of 30% to 60%. We know that a homosexual male has greater chances of finding homosexuals in his maternal ascendance. This suggests matriarcal transmission.
Three independent studies have shown a link between the transmission of masculine homosexuality and a certain region of the X chromosome.
Do cerebral differences often mentionned between the heterosexual and homosexual have any truth?
The problem is that adequate studies are difficlut to conduct. Observed differences in the preoptical region, for example, refer to structures too small to be seen with medical imagery. But smallness in no way invalidates importance. To give an idea, a nucleus of 1 mm^3 can contain 10 000 neurons, that can each have 1 000 connections, which accounts for ten million connections. This alone could define a logical circuit of impressive complexity.
I can conclude from completed studies that there are no doubt statistically significant differences in size for certain nuclei. But, there again, what shows up are average differences. There are overlaps. It is part of the answer, no more.
Finally, all these findings leave us with statistical results?
Undeniably. But taken as a whole, we are left with a pattern of findings in favor of a strong bilogical component. What true importance? Does it explain 50% of the variance, 80%? At this point, no one knows. But to deny it would be a form of denial.
If we accept a strong biological component, how would we explain this from an evolutionary point of view?
There are many hypothesis. The real issue is exclusive homosexuality. How could one explain that evolution, whih aims at maximising reproduction, could allow its persistent
presence? First of all, man is not alone. There is at least one species in which it exists in an undeniable fashion: the Rocky Mountain sheep. One sees them vigourously mounting another male, totally ignoring the female in heat. One would have to postulate a hidden advantage.
The most popular explanation is that of the hypersexuality of the women involved. A recent study shows that mothers, grand-mothers, aunts and cousins of homosexual men have more children than those of heterosexuals. Another hypothesis is that homosexuals, in the difficult history of our evolution, have served to help parents raise their children. In both hypothesis, selection favours genes that lead to homosexuality.
Are there yet arguments in favour of homosexuality as a cultural construct?
The most widespread idea comes from psychoanalysis, for whom -and I am simplifying - homosexuality would be the result of a non-resolved Oedipal complex. There are also constructivists, for whom sexual orientation comes from the environment.
Such theories meet with two major difficulties. There are no quantitative studies showing any kind of link between the child’s psychological history or the type of environment in which he was raised and subsequent ulterior sexual orientation. Thesecond, all to the contrary, is the vast quantity of examples showing the absence of such patterns of influence. Much has been made of the absent father. But there are millions of unwed mothers and the absence of a father in no way augments the prevalence of homosexuality.
There also exist traditional societies, such as Malaysia or within Micronesia, for example, where homosexual relations are imposed on adolescents before marriage. Neither there do we find any particular spike in homosexuaity at adult age. No more than for boys who had homosexual relations before schools were integrated. In truth, the frequency of homosexuality is pretty much constant for all societies, and as far as we can tell, for all epochs.
Interviewer Olivier Postel-Vinay
Jacques Balthazart, Biologie de l’homosexualité, Ed Mardaga, 304 p., 29 euros.
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