Re: eyes in cave animals drifting away?

From: Keith Henson (
Date: Thu 19 Feb 2004 - 14:38:06 GMT

  • Next message: Chris Taylor: "Re: eyes in cave animals drifting away?"

    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?

    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

    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 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

    =============================================================== This was distributed via the memetics list associated with the Journal of Memetics - Evolutionary Models of Information Transmission For information about the journal and the list (e.g. unsubscribing) see:

    This archive was generated by hypermail 2.1.5 : Thu 19 Feb 2004 - 14:42:05 GMT