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Population size and molecular clock?

Mike Syvanen syvanen at ucdavis.edu
Sun Jan 3 08:32:22 EST 1999

"Jose Mª Muiño" wrote:

>     Ayala proved that the variability affect the speed of evolution, no?
>     If we have a high speed of evolution we´ll have a high variability, no?
>     If we have a high variability we´ll have a high heterozygosity (H), no?
>     if we have a high heterozygosity (H) we´ll have a high Ne, no?
>     Which is the problem?
> larger populations experience more neutral
> mutations (2NeV), but each neutral mutation has a smaller probability of
> ultimate
> fixation (1/2Ne). Yes, but if Ne is very high some mutations can be the
> same, and this 2NeV news mutations are less (i.e: 2NeV-x, where x are
> mutations not news). Then K isn´t the same than V, isn´t it?

Ayala's 1969 "proof" is not acceptable.  Not because the logic is inherrently
flawed, but because it leads to a result that does not explain patterns of
molecular evolution as they are revealed in the sequence data.  To a first
approximation, the molecular clock is independent of population size.  There
are many well documented cases where the clock in one lineage must be
significantly different than that in another lineage.  However, I am aware of
no  example that the differences can be explained by differences in population
size.  Does anybody know of an example?

In short, Ayala's theory fails for lack of explanatory power;  Jukes and Cantor
and Kimura's pass that test.

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