Re: Evolution, "adaptation", and what's currently adaptive

Bryant (mycol1@unm.edu)
19 Sep 1996 07:35:09 -0600

In article <51h9p2$isn@news00.btx.dtag.de>,
Heiko Pawelczyk <weizenkeim@t-online.de> wrote:
>
>As biologist I have learnt that any gene, even that ones responsible
>for eye formation are subject to mutations. Organisms living in a
>lightless environment, therfore not needing their eyes anymore, are
>not impeded by reduced capabilities of their eyes. Hence there is no
>selection against these mutations and they begin to gather until the
>eye is more or less reduced.

Yes, that's the traditional take on eyelessness in cave critters.
Gerold's significant point, I think, was that drift alone might not be
the whole story; selection might *favor* the eyeless mutants because of
costs associated with developing or having eyes (metabolic costs or
parasite costs). Usually, sighted critters enjoy a greater net fitness
from seeing despite eyes' costs.

When eyes no longer provide such benefits, two things can happen.
Drift (mutation accumulation), as you point out, can cause eyelessness.
Or, as Gerold argued, selection can push eyelessness to fixation more
quickly than drift would. Bryant