Sunday, October 28, 2007

Genetics of Homosexuality

Homosexuality is not a disease, not evil, not morally wrong etc etc. What between 2 - 5 buffed people do in the comfort of their designer bedrooms (or in a public cubicle) is their own business. 'All power to them' i say.

On this point, i think the Catholic church has been 'barking up the wrong tree' for quite a while.

The practise of 'sodomy' is considered evil- and that would mean the Church should be targeting heterosexual couples to encourage them to have sex that is:

a) strictly peno-vaginal
b) non-contraceptified
c) done with the lights off

The church should, however, get their own house in order before criticising others. A few years ago the Portland diocese in Oregon decided to cure 'moral bankruptcy' with 'financial bankruptcy'- to avoid paying out too much in damages to victims of institutionalized paedophillia. Does anyone think this is not going on elsewhere? (saw a short for this film recently: "Deliver Us from Evil"- but don't think i'll be rushing to the megaplex to see it soon).

2. The scientific evidence overwhelmingly suggests human sexual orientation is 'given', rather than chosen. Among identical twin boys, if one is gay, the other has a 50 percent chance of also being gay. Among fraternal twins, who do not share the same DNA, there is only a 20 percent chance. The lack of 100% concordance between identical twins is probably the result of methylation of stretches of DNA.

3. There is almost certainly not a single gene that causes homosexuality- but like height or musical ability it is probably polygenic. It is also possible that it is related to fetal exposure to maternal hormonal changes etc- i.e. congenital but not truly 'genetic'.. (unless you consider the genes of the mother).

Homosexuality, however, does require an explanation. How could a series of genes that cause attraction to the same sex (and therefore be unlikely to be passed on) survive thousands/ millions of years of human evolution?

One idea is to compare it to cystic fibrosis- this disease is one of the most common recessive disorders (both carrier parents must have a copy of the gene for heir kids to have a 1:4 chance of the disease). This disease blocks a chloride channel, causing lung secretions to become sticky. The carriers of this gene are, however, perfectly healthy... AND may be protected against severe cases of cholera induced diarrhoea/dehydration.

As the saying goes: "Too much of a good thing..." is .. not a good ..thing. (Strange how that phrase seems to be just the front end and just sort of peters out .... )

So- what sort of advantage (in terms of getting laid) do a few gay genes give you? One idea is that they make males more communicative, flirty and attractive to women. Witness the rise of the metrosexual.. but really.. do women really go for guys with lip liner and eye shadow? Maybe EMO-chicks.

Another idea (New Scientist) is that the mothers of gay boys have a higher fecundity than other mothers (2.7 babies vs 2.4 babies on average in italy). So maybe the genes code for horniness in women (or heightened attraction to men)- and that a gay son who won't give you any grand-bambino's is worth the effort from the genetic point of view. I can't really understand this conclusion ... as i would have thought the number of children would have to be >3.4 to even the odds.

This same research found increased fertility rates ONLY ON THE MATERNAL SIDE. This suggests either a) genes on the X chromosome are at least partly responsible, or b) it's inherited thru mitochondrial DNA. Some researchers claim to have pinpointed a locus on the X chromosome Xq28 - though others have refuted this.

Perhaps the association is 'causative' in the other direction- i.e. families with lots of boys are more likely to have a gay son. This is known as the ominously labelled "Big Brother Effect"- and it has been shown that this is a biological effect- not an environmental one. In other words, it doesn't matter how many brothers you were brought up with (e.g. if you were adopted), but home many older male siblings you have.

None of the research seems to look at the genetics of Lesbianism... although i'm wondering if lesbian cave-women really had much of a choice anyway before being 'knucked' on the head.


  1. Anonymous2:44 AM

    Actually, I imagine that it dates back to the hunter gather days. There were a few select alpha males who did all the mating – and this was a good thing for it ensured that the best genes were passed on. However if roughly 50% of the pack was male then a number of men had no respective mate.

    I’m not saying that homosexuality developed as a result of this behavior but rather, that packs were more stable when fewer men fought over mates and as a result women are ‘wired’ to birth fewer alpha males. [See Fraternal Birth Order]

  2. hmmm.. not sure about this idea. Smacks of 'group selection'- a concept which has generally been discredited. Evolution works on individuals- not grops i.e. the critical issue is whether or not one ape-man has offspring before he dies. My genes don't care about your genes.

    even if true- it would still make it hard to explain why those 'gay' ape-men who didn't get the girls could pass their genes on till this day.

    there is an interesting concept called "The Homophobe's Paradox".. where the more restrictive the society, the more gay men try to 'fit in'.. get married, have kids and pass their gay genes on! (presumably to the dismay of the homophobe).


Whaddaya think?