From: Keith Henson (email@example.com)
Date: Thu 19 Feb 2004 - 14:38:06 GMT
At 01:21 AM 19/02/04 -0500, you wrote:
>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):
>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
That may be possible in some instances. In others, for insect sort of
things that feed on bat droppings, the population may be rather large.
>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
I don't know the answer to this, but do know how you would gather
evidence. There are a lot of different cave blind species including fish
and a lot of different populations as well. Has the majority shift been in
the direction of reduced metabolism or are there cases where the eyes are
just non-functional while still running the same metabolic load? I.e.,
going blind vs the eyes shrinking to tiny dots.
Eyes like other nerve tissue *are* expensive to operate. Additionally,
they are exposed and wet, making them costly in terms of protecting from
>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.
Relating this back to memetics, you would expect memetic drift where there
was little or no cost associated with a meme. I was considering styles as
an example, but that may not be drift. It is possible styles don't drift
but are driven in a kind of chaotic movement where the next style is
anything except the old one. I.e., driven to a cycle limited
"newness." (Women's skirts can only range from the floor to . . . .
) Open to speculation as to what psychological trait selected in the Pleistocene could be manifesting today to drive clothing styles. Are changing clothing styles a western culture feature only? Are men's clothing styles more stable in different cultures?
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