Re: Part 1 (of 3): What are major aspects of evolutionary theory?

On Mon, 05 Dec 2005 02:16:16 GMT, John Harshman
<jharshman.diespamdie@xxxxxxxxxxx> wrote:

<snip>

> Selection and drift are two different processes that can
>operate simultaneously. Of course any drift component always averages
>out to zero, since there is no force pushing it in any direction. But of
>course, also, no single case is average, and an allele subject only to
>drift has only two possible fates: extinction or fixation, with the
>relative probabilitie of each at any moment equal to 1-p and p,
>respectively, where p is the current frequency.
>

I disagree. The transmission of alleles from one generation to the
next is inherently a stochastic process based on probability
distributions. Whether an individual survives or not, whether it
reproduces or not, whether the offspring survive or not depends both
on phenotype (and genotype) and on plain dumb luck. Which of the
parental alleles get passed on to a particular gamete and which gamete
succeeds in fertilization depends on plain dumb luck (possibly with
some contribution of the genotype). The point is that the
probabilities are not uniform -- some alleles end up with a higher
probability of appearing in the next generation than others. You can
separate drift from selection conceptually by saying that the
deviation of probabilities from a uniform distribution is called
"selection" while the fact that there are probabilities present at all
is called "drift". But the biological processes at work are all
stochastic, probabilistic, with non-uniform probabilities.

So I amend my previous definition of drift where you misunderstand the
meaning of correlation and environment. How is this?

The transmission of alleles from generation to generation is a
stochastic process, depending on random factors expressed through
probability distributions. Therefore allele frequencies will behave
as a sort of "random walk" process, changing over generations. The
probability distribution need not be uniform, all alleles equally
likely to appear in the next generation. The deterministic change in
the frequency distribution (mean, variance, etc.) from generation to
generation due to the unequal probabilities (unequal "fitness") is
called "selection". The remaining variation in frequency
distribution, including that occurring even when the probability
distribution is uniform, is called "drift".


.

Relevant Pages

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    ... Of course any drift component always averages ... > parental alleles get passed on to a particular gamete and which gamete ... > probability of appearing in the next generation than others. ... > separate drift from selection conceptually by saying that the ...
    (talk.origins)
  • Re: Part 1 (of 3): What are major aspects of evolutionary theory?
    ... >> parental alleles get passed on to a particular gamete and which gamete ... >> probability of appearing in the next generation than others. ... >> deviation of probabilities from a uniform distribution is called ... because both variance of the ...
    (talk.origins)
  • Re: Is bipedalism neutral? (was Re: Claims Of Abuse)
    ... >>involved in the shift to bipedalism have drifted to fixation. ... >>and the mutation rate of these alleles. ... >>The probability of bipedalism evolving over that time scale is then the ... and want to know whether it was by drift or something else. ...
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