From: Keith Henson (hkhenson@rogers.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):
>
>http://cfpm.org/~majordom/memetics/2000/16576.html
>
>Has he ruled out the possibility of genetic drift?
Good point.
>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.
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
>process.
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
bacteria.
>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
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?
Keith Henson
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