Re: Evolution and Sexuality

From: Harnad, Stevan (
Date: Thu Mar 16 1995 - 09:41:52 GMT

> From: "Cornah, Deborah" <>
> Date: Thu, 16 Mar 1995 08:45:37 GMT
> In last week's lecture, Stevan was pondering why homosexuals haven't
> "priced themselves out of the market", so to speak. Whilst I'm sure he
> does have an explanation, surely he already answered it himself earlier
> in the lecture. That is, adaptation occurs when there's a change in the
> environment that provides some individuals with an increased chance of
> survival, thus eliminating those who don't have that particular
> advantage.

That's fine insofar as homosexuality as an occasional variant on
heterosexuality is concerned (we don't have to be constantly eating
nutritious food either, just often enough to get by). But (1) IF there
is a disposition toward exclusive homosexuality and (2) IF that
disposition is genetic, then that disposition would eliminate itself
form the gene pool pretty fast (especially if it were dominant, with
complete penetrance), whether it appeared in the EEA or the present
day. If not, we need an explanation of why not.

So what that probably means that if homosexual preference is
constitutional at all, it is either not genetically transmitted, or it
is complex, with incomplete penetrance. OR some role peculiar to
homosexual kin in an inclusive fitness model made it adaptive (for
familes as a whole) to foster and retain such a specialist

That's why I said it was like the problem of explaining the persistence
of the minority left-handed population.

Another possibility, of course, is that constitutional (as opposed to
purely cultural) homosexuality is not genetic at all, but developmental,
with a developmental accident hormonally altering the foetal brain.

> Well, maybe its just that, as yet, the environment neither favours nor
> dislikes individuals who prefer to have homosexual sex? Yes. I KNOW
> that distally, homosexuality is difficult to explain, BUT let's not
> forget that Darwin also blessed us with the ability to think and
> reason. That's why I said "prefer": we can choose to act against the
> distal influences of our behaviour, in order to fulfil the proximal
> desires, and why not?

This is fine for explaining homosexuality by idiosyncratic choice, but
not genetically disposed homosexuality.

> By the way, is it not so that many homosexuals also enjoy heterosexual
> sex? So if you really must have a Darwinian explanation, there it is.

There seems to be a core of exclusive homosexuals who do not feel they are
bisexual, and they feel they were born that way. If they are right, and
their disposition is genetic...

> Personally, I'm not sure such debates actually do a lot to further the
> progression of our species, so on the question about what should and
> shouldn't be published, I do respect freedom of speech, but when does
> sociobiological (and other) research stop providing USEFUL insights
> into the nature of human behaviour?

Could one not have asked the same question about every other topic
discussed in the course so far? (And, let me assure you, it will
continue to be a fair question about the later topics. Nor is this just
true of "Debates" topics, or Psychological ones in general: Once you
look closely at what humanity knows, very little of it can be
uncontestably defended as USEFUL...)

Chrs, Stevan

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