Re: latent mutation

From: Scott Chase (ecphoric@hotmail.com)
Date: Wed 07 May 2003 - 03:37:08 GMT

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    >From: Ray Recchia <rrecchia@mail.clarityconnect.com>
    >Reply-To: memetics@mmu.ac.uk
    >To: memetics@mmu.ac.uk
    >Subject: Re: latent mutation
    >Date: Mon, 05 May 2003 21:14:48 -0400
    >
    >Thanks for the effort Chris. Don't sweat it too much. I may try to look
    >Wilson after I finish his book and I'll see if he has any examples
    >
    >Jake, I think the term "atavism" is fairly close to what I'm looking for,
    >but it doesn't seem quite the same. Atavism would seem to cover the stage
    >where the spotting mechanism disappears with point mutations but not the
    >potentially quicker re-evolution of the spots again when the environmental
    >condition for their selection re-appears.
    >
    >The book 'Darwin's Cathedral' by the way has more to do with cultural
    >selection of religions. The idea for latent adaptation came when he was
    >discussing guppy species differences in response to different types of
    >predation. Because the differences in predation seem to me to be things
    >that might fluctuate within the environment on a fairly frequent basis I
    >thought something like a 'latent adaptation' might end up present within
    >the species.
    >
    >At 05:48 PM 5/5/2003 -0700, you wrote:
    >>aren't point mutations those undesirable things that "bad" dna have? heh.
    >>I
    >>don't think that species would evolve to include point mutations since
    >>this
    >>would mean screwing up all of their dna. think more. if a species is both
    >>gray and spotted, when gray is good and spots are bad (since it wouldn't
    >>un-evolve the spots hm?) won't it like, get killed? that's not good. read
    >>selfish gene, by dawkins. best dna book out there.
    >>
    >>always, sabrina
    >
    >I don't think you got it. I'll spell it out a bit more clearly
    >
    >Under environmental condition 1 a bland grey animal is better camouflaged.
    >
    >Environmental condition 2 arrives. Grey bland animals are no longer the
    >best camouflage
    >
    >Over time our species slowly evolves the ability to appear with spots.
    >Under environmental condition 2 spotted animals are better camouflaged.
    >
    >Environmental condition 1 returns. Now spots are no longer the best
    >camouflage again.
    >
    >Instead of completely eliminating all the genes for spots, they are just
    >disabled with point mutations that prevent the genes from expressing
    >themselves and the species returns to its grey state.
    >
    >Environmental condition 2 returns. Now spotting can reappear much more
    >quickly because instead of having to re-evolve the entire spotting
    >mechanism only the disabling point mutations have to be reversed.
    >
    >I don't think this is something Dawkins discusses, although I see nothing
    >in his ideas that would contradict the possibility of it happening. I did
    >read 'The Selfish Gene' and I agree that it is quite a good book.
    >
    >
    I don't know if polyphenism would explain the case you're talking about, but it's something to think about since polyphenism is a phenomenon that takes us beyond genetic diferences ( relating to allelic frequency changes) in populations.

    In polyphenism (sometimes called polymorphism) there's not a genetic difference between individuals responsible for difference in phnotypic appearance, but differences in development. Most individuals in a population have the same genetic repertoire, but they express it differently under diferent environmental circumstances due to some cue which induces a cascade of developmental events (a switch) which sends form A and form B down separate paths. One type of polyphenism is seasonal polyphenism, of which seasonal differences in coat color in mammals such as rabbits wuld be an example. Seasonal polyphenism occurs in butterflies and moths. Environmental cues which might trigger such discrete differences in form might be something such as photoperiod or temperature. Scott Gilbert discusses this in decent detail in his text _Developmental Biology_.

    Maybe, if the basis is genetic difference in individuals within a popluation across time, there might be two alleles involved where at one time one form becomes rare, but when the adaptive lanscape shifts back, this rare form becomes a selective advantage and the frequencies eventually shift back to a state where this form becomes common and the other rare. If there's migration from an area where the situation is reversed, an occasional migrant or so could bring their alleles into the population where they have been rare but presently adaptive. This "gene flow" plus mutation could be factors in subsequent population changes (accounting for population size and all that).

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