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From: pell@boulder.Colorado.EDU (Anthony Pelletier)
Newsgroups: sci.misc,sci.bio,soc.women
Subject: Re: Univerrsal Common Female Ancestor
Message-ID: <2567@sigi.Colorado.EDU>
Date: Wed, 14-Oct-87 13:32:30 EDT
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Posted: Wed Oct 14 13:32:30 1987
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(Colin Jenkins) writes: (in response to me)
>> 
>> I'm confused here.  Would anyone have suggested that humans evoloved more
>> than once? 
>> 
>> -tony
>
Colin:

>I recall from my genetics courses that many genes mutate in similar ways with
>significant statistical frequencies.  Of course, this doesn't *prove* anything
>about the existance of multiple or singular ancestors,but [it is possible]
>
>My impression of evolution is not that a single momentous event could have
>occurred, but rather a series of such events.  If, after each significant
>mutation, a large quantity of offspring was produced, then the next step in
>the sequence would have a significant statistical likelihood in a large base
>of individuals, not just one, and so on for each significant mutation.
>
>						Colin

Of course we are arguing in the dark here--proof would be hard to come by.
In the early-going of a rather good book called "Molecular Biology of the
Cell" (Alberts, Bray, Lewis, Raff, Roberts et al.), the authers admit there
bias that each major event in evolution occurred only once, one primordial
cell, one eukariote, one metazoan on down the line.
Our mitochondria should be direct decendants of not only the first Human, but
also the first euk.  It seem logical that, given speciation of a new mammal
has not been observed as long as man has been keeping track, it is a rare event.
I find it hard to believe that it happened more than once, let alone more
than once in a small enough area that these different H. sapiens could make
one breeding population.
I always assumed that the reason archiologists argue over whose fosil is
older has to do with the assumption that the younger ones are Decended
from the older, not different lines that are co-incident.

I imagine speciation in the following way (here I am way out of my line):
Some event occurs (eg. a chromosome re-arrangement) such that an offspring can
not mate productively, or, at least not have fertile offspring, with any
members of the group except its parent or perhaps its siblings.
Offsping of these matings are also constrained in there mating.  You now
have a separate breeding population.  If the new population has a selective
advantage, you have a new, meta-stable species.  Now, the new species might
well co-exist with the old for some time, amassing some numbers of individuals
that would seem to be in one population with the parent species. But they
would be a separate breeding population.  
The notion of a group of organisms going off into a secluded area and evolving
together into a new species seems absurd to me.  I can buy that selection on
all of them is the same, but the random element of evolution, mutation, cannot
possibly occur in them all.  More likely, the mixed population, such as the
one I describe exists until some selective pressure kills off the parent
species.

just rambling
-tony