From: Scott Chase (ecphoric@hotmail.com)
Date: Thu 19 Feb 2004 - 06:21:11 GMT
In a couple recent posts Keith has used the example of cave animals
losing their eyes due to lack of light. In this post he tells the
adaptionist tale of this loss being related to metabolic costs (ie- eyes
too expensive to build so selected against):
http://cfpm.org/~majordom/memetics/2000/16576.html
Has he ruled out the possibility of genetic drift? In an environment
that lacks light, the major selective pressure for maintaining eyes has
been negated, thus mutations of eye development related genes would be
selectively neutral. Populations of cave dwelling animals might be quite
small. Mutations of eye genes might accumulate, due to not being removed
by selection. Eyes, as a structure, would deteriorate and the animals
become blind, without metabolic cost being a significant factor in the
process.
Futuyma's text says one possibility is that (p. 423) : "mutations that
cause degeneration of an unused character become fixed by genetic drift
because variations in the character are selectively neutral". Selection
is another and an hypothesis is explored which supports selection but it
is noted that in some instances genetic drift may play a role.
Futuyma DJ. 1997. Evolutionary Biology. Sinauer Associates, Inc.
Sunderland, Massachusetts
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