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From: Tim Tyler <t...@tt1.org>
Newsgroups: talk.origins
Subject: Re: Why is there male and female?
Date: Sat, 29 Jun 2002 08:32:26 +0000 (UTC)
Organization: University of Bristol, UK
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badgerboy <sexwithbadg...@hotmail.com> wrote:

: why is it that we ended up with two sexes that can't breed with other
: members of the same sex?

: Surely it wouldn't be too difficult for an organism to evolve a
: mechanism whereby either sex can produce offspring (having the sperm
: and egg combined, being produced by any member of the species).  The
: advantages for this, not least in terms of preventing inbreeding,
: would be great.  I'm sure it goes on in some organisms (in a way), but
: why is there any survival advantage of making sure that an organism
: can only breed with half of its own species?

Why are we not hermaphrodites?

Two popular books that examine this question are:

"The Red Queen" - Matt Ridley
"Mendel's Demon" - Mark Ridley [authors not closely related]

While the answer they provide is facinating, I also think it is not
entirely correct.

Their theory fails to explain why many plants are hermaphrodites - while
few animals are.

It also apparently predicts that aliens/far-future lifeforms will
/probably/ be hermaphrodites.

I think the explanation misses an important element of the advantages
of dividing the sexes in mobile creatures.

That is that the adaptions that work best for distributing seed to many
places are different from those that work best for giving
birth.  Combining these both in a single organism would mean that it is
not optimally adapted to either role.

That may not be the explanation for the /origin/ of the sexes being 
dimorphic - but it contributes to its /maintenance/ - and it seems likely
to persist when the other advantages of divided sexes vanish.
-- 
__________
 |im |yler  http://timtyler.org/  t...@tt1.org