Darwin Day 2015 Questions

#1 Is Homosexuality Nature's Population Control?

(Music playing)

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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