On Sat, 1 Nov 2003 04:49:54 +0000 (UTC),
name_and_address_supplied{at}hotmail.com (Name And Address Supplied)
wrote:

>"Anon."  wrote
in message news:...
>> TWINBLUE wrote:
>> >>is it the case that the divisions into gender is as close
as you>can get,
>> > 
>> > evolutionary speaking, to something inevitable?>
>> > 
>> > While there may be other solutions to the
>> > problem of genitic diversity and evolution
>> > I would expect that where ever you find life
>> > you will find sex. Since more than two varities of sex would
be a bit unhandy
>> > evolutionwise you would likely find most 
>> > creatures in the universe that are large enough to see with
the naked eye are
>> > divided into "male" and "female".
>> > 
>> What's wrong with a single sex?  I think you have to start by asking why 
>> most sexual organisms have multiple mating types (there - my solution to 
>> the sex/gender semantic debate!  Do as mycologists do!), and then you 
>> can go on to ask about the specialisation of mating types into 
>> differentiable sexes.
>>
>
>Mating types and sexes aren't quite the same.  The former are possibly
>helpful for preventing inbreeding where this might be harmful.  It
>doesn't seem to represent divergence in strategy in any sense, whereas
>males and females are (with a few exceptions) associated with a host
>of stereotypical adaptations which appear to be geared towards
>definite, divergent strategies.
>
>In some species there are dimorphisms within, say, males, relating to
>reproductive strategies.  Perhaps these should be regarded as similar
>to separation of sexes.  For example, the well known RPS game played
>by orange, blue and red morphs of male lizards.  Perhaps in that
>species we should recognise that there are 4 sexes (three different
>male types and a female), or perhaps 2 sexes but with one including 3
>subsexes?
>
>Or maybe not . . .

What you are describing is a whole continuum of reproductve
strategies.  Sexual dimorphism varies enormously, from strikingly
different male and female appearance and behavior to complete identify
between individual organisms (as in hermaphroditic animals and perfect
flowers) but formation of different gametes, to only chemical
differences in apparently identical gametes (mating types and
isogamy).

There does seem to be strong selective pressure to favor sexual
reproduction, meanng simply alternation of haploid and diploid states
and the possibility of genetic recombination.  This does not require
any sort of sexual differentiation or dimorphism.  The "mating type"
system is true sexual reproduction.

Given that two gametes must get together, if the gametes are not
already the usual motile form of the species, there does seem to be
strong selective pressure to favor one gamete  taking on the task of
moving to the other, usually becoming small and motile, while the
other taking on the task of providing nutrients to help ensure the
survival of the zygote, usually becoming large and stationary.  That
produces what we call two sexes, with male structures producing the
motile gamete (sperm) and female structures producing the nutritive
gamete (egg).  There is still no need to invoke different body forms
or behaviors.
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