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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: sci.bio
Subject: Blind cave fish
Message-ID: <1340@cybvax0.UUCP>
Date: Wed, 7-Jan-87 11:46:24 EST
Article-I.D.: cybvax0.1340
Posted: Wed Jan  7 11:46:24 1987
Date-Received: Thu, 8-Jan-87 00:42:45 EST
References: <741@aecom.UUCP> <927@husc6.UUCP> <124@bcsaic.UUCP>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Distribution: na
Organization: Cybermation, Inc., Cambridge, MA
Lines: 26

In article <124@bcsaic.UUCP> michaelm@bcsaic.UUCP (Michael Maxwell) writes:
> I suggested this [genetic drift] 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?

Neither of these explanations strike me as correct.

I would attribute blindness of cave animals (something which has arisen many
times independently) to accumulation of mutations which normally would be
selected against.  When selection pressure is eliminated by a dark habitat,
developmental mutations that cause blindness can accumulate, where normally
they would be immediately eliminated.  Without selection pressure, there is
no limit to the number of mutations that can accumulate.

It is also possible that there is some advantage to eliminating eyes, in
terms of vulnerability to injury, disease, etc., or simply in reduced
energy costs.

Both of these are independent of population size, and thus not the same as
genetic drift.
-- 

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