tomhendricks474{at}cs.com (TomHendricks474) wrote in message
news:...
> A genetic textbook says, "Four principal causes of change in the 
> frequency of alleles are usually distinguised:
> Mutation, Migration, Natural Selection, and Random genetic drift.
> 
> Yet in the end isn't it Natural Selection that makes the final call?
> 
> For instance all the mutation, migration, and random genetic drift
> won't amount to much if the environment stays the same.
> Then convergent evolution happens.

Perhaps, but the statement specifically discusses genetical evolution,
not phenotypic evolution.  A dolphin might look like a shark, but
their genetics will be very different.  And which particular alleles
reach which particular frequencies will often depend strongly on
forces such as drift.  If the selection coefficient is less than the
reciprocal of the effective population size, then drift is expected to
predominate.  If mutation is of the same order of magnitude as
selection, then we expect a not insignificant genetic load.  Migration
is conceptually similar to migration, so an analogous migration load
can be influential.
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