August 16, 2008

Why are there homosexuals?

Homosexuality should not exist. That is not a political or moral statement- but a statement derived from evolutionary theory. Evolution rewards reproduction. Most human traits contribute to reproductive success ultimately or are neutral to it. But homosexuality does not contribute to reproduction because a pair of men or a pair of women cannot have children independently of scientific aid. We know that homosexuality is an ancient part of human beings- we know that it goes on in the animal kingdom. We also know that it is partly genetic. Why therefore has this behaviour, which should have died out in a generation, survived all the way to the present day?

There was an interesting article in Psychology Today about just this issue. The author Robert Kunzig presents a kalaidescope of factors. The most interesting is what Kunzig suggests about two particular traits which happen before the birth of a male homosexual. The first is genetic. This is really interesting, what I was arguing above was based around the survival of a particular individual's genes- but of course that is a failure to understand evolution, what I should have been talking about was the survival of genes down the generation. Take that angle and suddenly the homosexuality question becomes easier. An Italian study reveals that the mothers and aunts of homosexual boys have more children than the base population, they have more sexual encounters and more partners. Essentially the same genetic factor that makes homosexuals in men, makes women more fecund and hence reproduce themselves more- sometimes they produce an evolutionary dead end- a homosexual boy- but to offset that they produce more children.

Another factor though is present in the research- which is equally interesting and that has to do with the womb. As a non-scientist I often think you get your clump of genetic material- and you get your baby at the other end and there is no change between the two. The only factors which decide a child's character are its genes and the way that its nurture in the world shapes the genetic impact. That misses a step. One of the interesting things about homosexuality is what happens in the womb. Kunzig suggests based on research that the number of elder biological brothers (whether they are present in childhood or not) influences whether he is homosexual by up to a third. It isn't the presence of brothers in childhood- non-biological brothers from a different womb don't matter but biologic brothers who are not around in childhood do- but that they come out of the same womb. The Biologists believe that this is because of the way that a woman's womb reacts to a male child- she produces antibodies and an immune response which affects the foetus's brain and feminises it. That immune response is stronger with every male child born. The argument is interesting- and implies another cost benefit association for the woman because women with more powerful immune systems end up with more homosexual sons- her health is offset against producing a son who will not reproduce.

These are not the answers- and it is important to realise that for the majority of human history, many homosexuals have reproduced. It is only very recently that homosexuals have been able to live as homosexuals instead of unhappily existing in a heterosexual relationship or living in the closet. The fact that my original model is wrong- that homosexuals do sometimes produce children is something else to throw into the mix. Basically it substantiates the idea that there is something advantageous for his parents in having a homosexual son- particularly as we have seen for his mother. These aren't the full answers- but they are interesting as they explain in part what to me has always been a problem- why does evolution produce an individual who does not wish to reproduce? The answer seems to lie in the fact that the rest of his family reproduce more, and that his mother is healthier and is reacting to his older brothers. This does not explain all homosexuality- but it explains some and further research will illuminate the topic even more.


Anonymous said...

Why does homosexuality exist? I'll be buggered if I know.

RobF said...

There's also the rather controversial theory which suggests that evolution can select for social factors, as well as for straight-out transmission of genes.

At a base level, this postulates that a gene which improves the survival rate of a family or tribal group can persist, even if it disadvantages the specific individual in whom it is expressed. So, for instance, you might find an evolutionary advantage to having homosexual adults in a tribe, because they can work/fight/hunt for the tribe without having to focus on caring for their own offspring.

They won't reproduce (probably), but their brothers and sisters will be more fruitful as a result of their contribution - and so, a mutation which provides a chance, rather than a certainty, of homosexuality is passed on to another generation.

Like I said, it's controversial - a lot of evolutionary biologists don't accept that mechanisms like this exist in evolution, at least not as we understand it at this point. However, it's another useful explanation to add to those which you present.

Certainly, any view which says that homosexuality should not exist due to how evolution works is clearly incorrect - the inalienable fact remains that homosexuality does exist, and our inability to explain this simply reflects our ignorance regarding evolution.

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Jennie said...

"any view which says that homosexuality should not exist due to how evolution works is clearly incorrect - the inalienable fact remains that homosexuality does exist, and our inability to explain this simply reflects our ignorance regarding evolution."

This. Also, I'd be wary of saying that homosexual men are simply "feminised" males. Who you are attracted to does not equate to whether your personality is stereotypically one gender or the other at all.

Gabbe said...

I'm often embarrassed by the petty logic my fellow scientists sometimes display. It's not their fault, the whole of the biology field is plagued by "the single cause" for many biological processes. This is commonly a push from some fellas to promote their research and its impact, not to open routes for greater understanding of nature.

The case of homosexuality is even worse: scientists who work in the area are sometimes downright clueless of the "clinical" manifestation of the "condition." They work based on common assumptions, like Jennie said, that all homosexuals are somewhat feminized and therefore must be a homormonal unbalanced somewhere that explains the whole case. So untrue - as biology shows, similar phenotypes can have many causes, synergetic or not, genetic or developmental. Then comes the pitiful attempts to put it in the evolutionary limelight, explaining - all very hypothetically, mind you - that it must have some sort of advantage to be preserved in history, probably in helping to raise children or as by-product of hearty mothers. Har har. If this hereditary genetic base was true, I would believe there must be some fluctuations between the rate of homosexuality between different isolated cultures, something that can be tested. However, measuring such rates is nearly impossible to do with precision due to heavy cultural influences in the "out" factor. Also, was the hormonal factor true, there ought to be quite more homosexuals in the past then today, which I'm not sure it would be the case.

I personally believe homosexuality has many causes, not necessarily all of them active in the same individual, that leads to similar but not equal, phenotype - which is attraction to other men. I also believe that like many syndromes, if mostly genetically based, it must be sprouting from natural mutation in the hotspots of some mysterious gene or group of genes - surely group-dependant. That would explain the somewhat ubiquitous distribution of it among the Animalia and also its frequency. It can also have other causes in the different groups and these causes can converge to a common phenotype or not, may act independently or not. For example, it's well known in humans, at least, that the neuronal synapse formation during the embryonary phase and early childhood is fundamental to set up our brain functions. This ultimately determine how are we answering to the environment and very probably our psychological traits. This process is somewhat random and irreversible and may be one of the non-genetic causes of homosexuality - or maybe it could be a enhancing factor of it in synergy with the genetics, or a supressor, you never know.

Again, this confuse post was just to clarify (the irony!) that biological science is far, far from being a precise science and you must take every "single explanation" for any biological process with a grain of salt - specially if it involves molecular biology (my field of work.) We still know very little how the seemingly infitine number of biological process working at the same time reacting with the seemingly infinite environmental and physical factors work truly. We can only speculate by moving some molecular levers to see what happens.

Gracchi said...

Jennie yes I was rather surprised by the 'feminised' brain stuff- I wasn't sure that homosexuals or heterosexual men are more 'female' and to be honest am sceptical about whether women are more 'female'. You'll notice I didn't use that example.

I do think that the stuff about birth order is interesting- partly because that kind of chemical change seems quite plausibel to me- in that an immune response to a second child would be interesting- it would be fascinating to know if there was any research on sisters as well as brothers for a homosexual man. And the stuff on the way that homosexuality might be a follow up to other kinds of selection.

Overall though I think I gave in what I wrote too much of an impression that I supported 100% teh article- I'm not sure I do reflecting on it. I think the suggestions about the birth order and the family size are interesting thoughts- but stuff about feminized brains isn't that interesting- the evidence about voice pitch (that gay men tend to be as low as straight men) should provoke some scepticism about the idea that gay men are generally more womanly than straight men. But the stuff about genetic selection and the womb I think is more interesting- I should have made it clearer that my article was a selective abstraction rather than a total absorption of the ideas in Psychology Today.

The Organic Viking said...

Interesting stuff, as ever. But why do these studies on homosexuality nearly always focus on men. I know this is a bit of a sweeping statement, but there seem to have been a fair number of scientific that point towards male homosexuality as being conditioned before birth in some way, while much less has been said about women. As a homosexual woman, I frankly couldn't care less about WHY I or anyone else is gay, all that matters to me is acceptance and the freedom to live a normal life within my society, and I sometimes worry that scientific attempts to work out the origins of homoseuxal orientation carry with them far too much risk.

Interesting point made by Gabbe. Indeed, given the vastly greater number of children had by most mothers both in past societies and in non-first world societities today, you would except the middle ages, for example, to be absolutely dripping with homosexuals. Perhaps they were, but cultural pressures make up for a lot. maybe that's what all the monasteries were for.

893748skldkdj said...

Homosexuality may exist as a deterrent to overpopulation by helping to prevent the number of members in a given community from expanding beyond the food supply. There's your evolutionary benefit.
Just my opinion; I'm not a scientist, either.

Anonymous said...

an observation regarding the last part of your post, where you say homosexuals don't wish to reproduce.

just because they can't have babies with the people they're attracted to doesn't mean they wouldn't like to have babies. i haven't seen studies of maternal instincts in lesbians, for example, but i imagine there's been cases of homosexuals having a heterosexual relation to have kids.

you've mentioned something similar in your post, i just wanted to draw attention to it