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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: net.origins
Subject: Re: Innocent Question
Message-ID: <528@cybvax0.UUCP>
Date: Thu, 9-May-85 14:10:17 EDT
Article-I.D.: cybvax0.528
Posted: Thu May  9 14:10:17 1985
Date-Received: Mon, 10-Jun-85 05:35:23 EDT
References: <1534@aecom.UUCP>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Distribution: net
Organization: Cybermation, Inc., Cambridge, MA
Lines: 34

In article <1534@aecom.UUCP> berger@aecom.UUCP (Mitchell Berger) writes:
> I was just wonderin'... If evolution happened in abrupt
> changes, wouldn't two animals have to undergo the same
> (or a similar) change? I mean, if in each step the new
> species can't breed with the old, we would need two of
> the new species in order to get something started. 
> What's the chance that there are two animals, 1 male and
> female, within the general vicinity (close enough so that
> they could find eachother), undergo the same drastic change
> in the same generation?

This requirement would only be true in certain special cases.

If the change formed a sexual reproductive barrier and if the organism was
incapable of producing offspring without a different sexual partner.

That's why there is an emphasis on gradualism in evolution.  (Even punctuated
equilibrium doesn't require the excessively hasty change you suggest.)

However, there are organisms where that sort of change can occur.  One
example is autopolyploidy in plants.  If the plant produces both pollen and
ovules, it can produce sexual offspring with itself.  Or, (in automixis)
the plant can produce seeds from somatic cells until it encounters
another that it can interbreed with (a common occurence in dandelions and
rice.)  Or, it can propagate vegetatively without seeds until a partner
shows up.

In the animal kingdom, there are also numerous possibilities.  Parthenogenesis
can make do until a partner appears (as in whiptail lizards and numerous
fish).  Some mites with haploid males can produce a male offspring, mate
with it, and then raise daughters.
-- 

Mike Huybensz		...decvax!genrad!mit-eddie!cybvax0!mrh