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Re: Information theory, entropy, and evo
Read, Dwight ANTHRO (Read@ANTHRO.SSCNET.UCLA.EDU)
Mon, 20 Feb 1995 16:52:00 PST
This is in reply to Yee's post:
In-Reply-To: <no.id> from "Steve Mizrach" at Feb 20, 95 02:00:13 am
Steve Mizrach writes:
> Anyway, not to go into a lot of detail here, but Campbell suggests the
> rather interesting hypothesis that the main problem with the neo-Darwinian
> evolutionary synthesis is that it considers all possible "sentences" formed
> from the DNA "alphabet" to be equally probable.
> Anyway, Campbell suggests that there may be a certain redundancy built into
> DNA (evidence for which comes out of the "jumping genes" theory of Barbara
> McClintock and the Human Genome Project) - a "grammar" if you will that
> constrains DNA 'messages' and guards against errors. All possible mutations
> (reshuffling of genetic information) are therefore not equally probable.
> Some sentences are more likely than others.
This is hardly evidence against neo-Darwinism or the modern synthesis,
surely? It's no different to meiotic drive, which has been known about
for decades.
My reply to Yee:
Darwin's orginal formulation is largely based on the idea that there are some
kind of unit that can undergo mutation (source of variation) and increase or
decrease in frequency within a population (effect of selection). The
original formulation essentially assumed that a system would be in stasis
without the driving force of evolution.
Neutral mutations and drift required a modification of this framework by
virtue of the possibility of allele frequencies changing stochastically, even
allowing for replacement of an existing allele by a new, mutant allele in the
absence of any selective effects. Neutral mutations do not invalidate the
general selectionist framework, but did require certain modifications; e.g.,
stasis is not the null condition in the absence of selective effects.
Recent work on self-organizing systems suggests that structures can
arise prior to selection (the self-organizing structure) and so selection
need not be invoked to account for the existence of these structures.
Selection might favor the conditions which give rise to the self organizing
structure, so that there could be selection at more of a macro, rather than
a micro level. Again, this does not negate the selectionist framework, only
that certain modifications will be needed such as macro structures possibly
may be introduced as a unity rather than being built up piece by piece, as it
were--i.e., macro evolution may be more than micro evolution writ large.
I take it that Campbell is suggesting yet another way in which what selection
acts on may be more complex than single alleles, namely that there may be
some kind of internal organization or structure to DNA that affects what
kinds of mutations are possible (my reading of what has been said here about
Campbell's argument is that this is not meiotic drive). Again, this will not
negate the selectionist framework. Rather, that it will (if the idea pans
out) require further modifications. (I am intrigued by Campbell's argument as
I have long thought that the phenomena which are produced via DNA has a level
of complexity that is hard to accomdate within DNA which is "merely" a
sequence of alleles each acting as an independent unit.)
So I suspect that what we will be seeing is more evidence of the way in which
the model of individual alleles independently susceptible to mutation and
selection will need modification is too simplistic and that more and more
structure (IMHO) will be identified that comes about not via selection
(though selection will act on what is produced), but via the whole nature of
chemical and biological processes involved.
D. Read
READ@ANTHRO.SSCNET.UCLA.EDU
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