Re: biology

From: David Campbell (bivalve@mailserv0.isis.unc.edu)
Date: Thu Jan 13 2000 - 13:24:53 EST

  • Next message: jeff witters: "*Physical Constants"

    >Could you please include:
    >
    >1) Development of biochemical processes step by step showing adaptive
    >utility of each step.
    >Photoactivity must be connected to a set re-set mechanism and must be
    >connected to the
    >neorological system in some fashion.

    Explaining this would require a lot of patience on your part, as someone
    has to find out what all the biochemical processes are in the first place,
    and I have to read them as well as finish my dissertation and get a job. I
    am not a biochemist, so I do not know what is known about all of these. I
    believe there are some ideas on the evolutionary precursors of
    photosensitive pigments, but do not remember any detail. I can describe
    the biochemical evolution of primate red-green color vision, if that would
    be of interest.

    From a morphological point of view, any sort of eye from a single
    photosensitive cell on up is useful. The wide range of eye types in living
    and fossil organisms suggests that there are quite a few genetic
    combinations that would be functional intermediates.

    For the most simple eye function, all that is needed is a connection to the
    appropriate response function. A brain is not necessary, just a neuron.
    For example, the ark shell in the aquarium that closed its valves when I
    walked past diid not have a brain. It did have simple eyes, enabling it to
    detect a moving shadow, and some sort of connection to the adductor muscles
    to send the message, but no image processing. Even its eyes are well ahead
    of the simplest.

    >Also, I want to know the purported time frame for these mutations. That
    >is,
    >according to the geological record, every so often a nasty rock from
    >space kinda messed
    >things up.

    The oldest fossil eyes I know of are on Early Cambrian arthropods. These
    are moderately well-developed, suggesting older eyes existed. As soft
    parts, they do not necessarily fossilize well. The genetic mechanism
    builds on similar precursors in all bilaterian animals, but it is unknown
    whether this means that the ancestor of all bilaterians had very primitive
    eyes or whether it simply had a gene useful towards that end, which evolved
    in parallel in different groups.

    Complex eyes have evolved several different times. They also have been
    lost multiple times, making it difficult to tell exactly when they evolved
    in what group. Scallops have eyes but the glass scallops do not. However,
    glass scallops are predominantly deep water species, where eyes are not
    very useful. No fossil soft parts are known for scallops, so it is not
    sure whether scallops evolved eyes after they separated from glass scallops
    or whether the ancestral form had eyes and glass scallops lost them. Thus,
    the timing of the evolution of eyes in scallops is not very clear.

    Overall, the timing of eye evolution could have, as a maximum, between a
    billion and half a billion years. Groups such as the scallops have
    apparently evolved less complex eyes in a shorter period of time.

    >as all
    >> the intermediate steps are useful,
    >*********
    >
    >WOW. This is a great assertion. Want to support it with someting.
    >Please, fill us in.

    Again, I was thinking of the morphology. Even rudimentary eyes are useful
    for any organism not always in total darkness. If you can see something,
    you can respond to it. If you can see more clearly and have the mental
    ability, you can respond more precisely.

    >Reduction in the utility of an existing function is not very
    >convincing. You
    >still have a great processing unit collecting even mitigated
    >information.

    My point was not clear. If something evolved to the point of seeing as
    well as I do without glasses, it would be able to get a lot of informaiton
    from that. If it evolved better vision than that, it could get more
    information without having to hold things within a few inches of its eyes.

    > Really, can you count the bytes of information in
    >the eye
    >for example and then estimate the number of bytes of information that
    >could
    >be generated per generation and then the number of generations.
    >Something
    >to hang this on, just something.

    A rough number of generations would be a few hundred million.

    I'm not sure how to estimate the number of bytes that would be equivalent
    to the genetic code. The order as well as the base can be important.
    However, a lot of rearrangement and substitution are possible without
    changing the result. Large pieces of DNA can be duplicated in a single
    generation, greatly increasing the amount of data, but then mutations must
    occur in the relevant genes for anything novel to appear. For example, red
    and green color vision in primates is the result of a duplication and
    slight mutation in the ancestral gene. It does not take too much of a
    change in a molecule to shift the wavelength to which it is sensitive, so
    development of color vision by such mutations is not too surprising.

    David C.



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