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From: palmer@cit-vax.Caltech.Edu (David Palmer)
Newsgroups: net.bio
Subject: Re: speciefication
Message-ID: <507@cit-vax.Caltech.Edu>
Date: Sun, 25-May-86 00:59:34 EDT
Article-I.D.: cit-vax.507
Posted: Sun May 25 00:59:34 1986
Date-Received: Mon, 26-May-86 01:41:59 EDT
References: <7730@glacier.ARPA>
Reply-To: palmer@cit-vax.UUCP (David Palmer)
Organization: California Institute of Technology
Lines: 37

Organization : California Institute of Technology

In article <7730@glacier.ARPA> bhayes@glacier.ARPA (Barry Hayes) writes:
>...  But the division of organisms into species
>is fundamental, representing the genetic barrier of producing 
>fertile offspring.
>
>But one thing that has always troubled me is the arising of a new
>species from an old.  Given just about any situation I cannot see
>how a distinct species which cannot interbreed with any previous
>species can come out of a population.  What could do it other than 
>two or more simultaneous identically placed mutations?  It doesn't
>seem as if a species could get that lucky as often as it has happened.

Speciation is not as fundamental as you might think.  Interbreeding is
not transitive, if A can breed with B and B can breed with C, then
A cannot necessarily breed with C (where "breeding" means the creation
of fertile offspring).

	For example, I very much doubt that a chihuahua (sp) and
a great dane are interfertile, but we class them in the same
species because a chihuahua can breed with a dacschund (sp) and a
dacschund can breed with a spaniel, etc. until you get to the
great dane.  There are more extreme examples, for instance
clines, where you can have a set of animals spread geographically
along a line.  Two animals that are near each other on the line can
interbreed, but the breeding gets harder and harder as the distance
between them along the line gets longer and longer, and so the
animals at opposite ends of the line are intersterile.  There is a good
example involving a type of hawk along the Arctic circle.  This
cline actually has both ends at the same point (the line having passes
all the way around the pole) and the two types of hawk cannot interbreed.

			David Palmer

	"God is as real as I am,"  the old man said.
	My faith was restored, for I knew that Santa would never lie.