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Richard Dawkins: "My question is, for things such as homosexuality,
which people who argue against evolution ceaselessly will insist,
there appears to be no linear Darwinian reason to possess this trait."
Now that's a very common question; it's one of the commonest questions I get asked.
How can it be that homosexuality gets
passed on from generation to generation.
Why doesn't it just disappear? Why doesn't natural selection remove it?
Well, the first thing to say is that it's only a problem
if it's a genetically inherited thing.
And you need evidence for that.
And the evidence for that comes from twin studies.
If you take monozygotic twins, identical twins, and you find,
for anything - it doesn't have to be homosexuality,
for height or weight, or musical ability, anything you like -
and you find that identical twins, monozygotic twins,
are more like each other than non-identical twins,
significantly more like each other,
then that suggests that the characteristic concerned is heritable.
Heritable means that there is a genetic component to the variance
in the population with respect to the character concerned.
In the case of height,
in the case of musical ability and so on,
we find that to a greater or lesser extent,
there is a genetic component; there is heritability.
And in the case of homosexuality, yes, there is, too.
If you know the sexual orientation of one twin, then you're better able to predict
the sexual orientation of the other twin, if they are monozygotic,
than if they're dizygotic.
So there is heritability, which means we do have a Darwinian problem.
We do have to ask the question,
why is it that male homosexuality has survived down the generations,
given that one might think natural selection would get rid of it.
There are various things that are being suggested.
There's, for example, the worker bee hypothesis
that males can look after their nephews and nieces, for example,
rather than look after their own children.
And so, not being sexually active yourself,
not being heterosexually active yourself,
could not necessarily be selected against in natural selection because of that.
A related idea, which is a bit fanciful perhaps, is that in our wild ancestors
there might have been a time when dominant males, who had harems,
went off hunting, and left the women and children in charge of males that they could trust.
And you could say, I suppose, that an ostentatiously homosexual male
would be trustworthy to a dominant harem holding male.
But of course many homosexual males are actually bisexual to a greater or lesser extent.
So this might have produced, this might have provided,
an alternative way for males to get access to females.
As it were, pretend to be not interested in females,
not deliberately pretend, I'm not talking about that.
So that's another hypothesis, but I'm not
very keen on either of those two theories.
I prefer to say something rather more nuanced,
which is that when we talk about a gene for anything,
whether it's homosexuality or anything else,
we don't necessarily mean that the gene inevitably has that effect.
A gene only has the effect that it does in the right environment.
So it could be that a gene that has the effect of causing a male
to be homosexual in the present environment,
in our present technological environment, civilized environment,
would not have had that effect in a different environment.
A possible example, and this only is for example, there is absolutely no evidence for it,
a possible example would be
what if bottle feeding, as it were, brings the gene out,
brings out the effect of that gene?
What if a breastfed boy, who has this gene, is heterosexual
but a bottle fed boy, who has this gene, is homosexual?
Well, in the days before bottles were invented
that gene would not have expressed itself as homosexuality.
So now what we may be looking at is a different expression of the same gene.
Now I'm not wedded to that particular idea at all,
I find it a good example to get across the point
that the effect of a gene is not inevitably tied to it,
but depends upon the environment in which the individual is brought up.
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