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Richard Dawkins: Darwin was born
on the 12th of February 1809: Darwin Day.
In honor of Darwin Day we issued an
appeal for questions on
evolution that I might answer.
And I'm going to now answer them.
"I've always believed homosexuality
was nature's population control
so that we don't overpopulate. Thoughts?"
That's a very tempting error, not with
respect to homosexuality, but with respect
to the idea that nature does
population control. That's not the way nature works.
It's so tempting to think "Oh well,
things would be best for the species
so nature will do whatever it takes
to keep the species going."
And that's just not the way evolution works.
Natural selection works at the level
of the individual gene. So in order
for natural selection to favor
population control, natural selection would have to
favor a gene or genes in an individual
that limited that individual's reproduction.
Homosexuality would do that, but of course
it wouldn't actually be naturally selected
because the individual that doesn't have
the children doesn't pass on the genes
for not having children. In order for natural selection
to favor population control,
it would have to be the case that an
individual that has too many children
ends up rearing fewer. And this was
worked out by the great ornithologist David Lack
who studied clutch size in
various species of birds. A bird that lays
more than the optimum number of eggs ends
up rearing fewer, because there's not
enough food for them. A bird that begins
by laying too few eggs, also ends up
rearing fewer for more obvious reasons.
There's an optimum number of eggs which a
bird species will lay. That's the extent
of population control adaptation. So I am
afraid it couldn't be true that homosexuality
is an adaptation to keep the
population size down.
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