From: Chris Taylor (christ@ebi.ac.uk)
Date: Thu 19 Feb 2004 - 14:40:24 GMT
I think(...) that as a rule they go blind first, then the eyes begin to
disappear as structures -- basically gross morphology is the last to go
usually, so the most precise things are most vulnerable iyswim. So the
metabolically expensive things don't seem to stand out -- the nerves
stay attached, the mucosa open to insult. There is a gain to freeing
brain for other tasks I suppose, if you have that sort of brain, as
opposed to a sort of glorified ganglion.
Keith Henson wrote:
> 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
>
>
> ===============================================================
> 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: http://www.cpm.mmu.ac.uk/jom-emit
>
>
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Chris Taylor (christ@ebi.ac.uk) MIAPE Project -- psidev.sf.net ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ =============================================================== 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: http://www.cpm.mmu.ac.uk/jom-emit
This archive was generated by hypermail 2.1.5 : Thu 19 Feb 2004 - 14:51:50 GMT