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From: michaelm@bcsaic.UUCP (Michael Maxwell)
Newsgroups: sci.bio
Subject: Re: The Red Queen
Message-ID: <124@bcsaic.UUCP>
Date: Mon, 5-Jan-87 14:29:09 EST
Article-I.D.: bcsaic.124
Posted: Mon Jan  5 14:29:09 1987
Date-Received: Tue, 6-Jan-87 23:15:42 EST
References: <741@aecom.UUCP> <927@husc6.UUCP>
Reply-To: michaelm@bcsaic.UUCP (Michael Maxwell)
Distribution: na
Organization: Boeing Computer Services AI Center, Seattle
Lines: 37

In article <927@husc6.UUCP> gallagher@husc4.UUCP (paul gallagher) writes:
>For example, certain closely related agnostid trilobites seem to coexist
>through size displacement.  It was predicted that size displacement would
>have to be in the range of 1.28:1 in order to avoid competitive elimination.
>The fossils in question were investigated and did indeed show ratios in
>size of about 1.28:1.

I suppose I'm being lazy (I could look up the reference), but I gather that
these species of trilobites were quite similar morphologically, and lived in
quite similar (or identical) environments.  Has anybody suggested that these
were actually individuals of the *same* species (possibly of different sexes)?
I know next to nothing about trilobites, but it certainly sounds suspicious...
I seem to recall that several living `distinct' species have turned out to be
members of the same species which underwent fairly radical changes during
ontogeny (Parrotfishes come to mind).  BTW, how easy is it to tell male and
female trilobites apart?

>Another way a population might change without any change in its environment
>is genetic drift.  Any very small population has only a limited, random 
>sample of the genetic variability within a species, and whenever two
>individuals reproduce,  some alleles will be lost, since only one chromosome
>of each pair is passed down to the gametes.  Thus, in a small population,
>there could be an evolutionary change in gene frequencies just through random
>chance assortment.
>Again, this process may not be very important.

I suggested this in answer to an exam question once, as the origin of blind
(eyeless) cave fish.  (The incidence of eyeless fish is quite high, but for
obvious reasons the eyeless ones seldom make it very far in life up here.)
The professor didn't like my answer...his point was that there had to be a
selective advantage to blindness in cave life.  I didn't believe so at the
time, and I'm still skeptical.  Anyone care to comment?
-- 
Mike Maxwell
Boeing Advanced Technology Center
	arpa: michaelm@boeing.com
	uucp: uw-beaver!uw-june!bcsaic!michaelm