On Thu, 8 Apr 2004 04:41:17 +0000 (UTC), Jeffrey Turner
 wrote:

>Larry Moran wrote:
>
>
>> The current models of speciation emphasize allopatric speciation as
>> a major player. When species arise as a result of geographical
>> separation they do not directly complete for resources.
>
>Ah, there's the crux of the problem.  Species do indeed arise as a
>result of geographical separation and it is that geographical
>separation that is the driving force.  The crucial quality of species
>is that they cannot mate outside their own kind.  As soon as you have
>a geographical separation you create a separate species.  It is only
>in the context of competition for resources that it makes sense to
>talk about whether a mutation is beneficial, harmful or neutral.
>

This is not true.  Geographical separation alone does NOT create a
separate species.  Failure to interbreed strictly due to physical
separation does not count as a reproductive isolating mechanism. Once
you remove the geographical barrier, if there is no other isolating
mechanism then interbreeding will quickly merge the two gene pools and
eliminate any differences that may have developed during the
separation.  The same thing happens is there is sufficient migration
between the two incompletely isolated populations.

What geographical separation does is eliminate the interbreeding that
keeps the gene pool intact.  Geographical separation also usually
means small population sizes in at least one of the groups, increasing
the probability of drift.  And, of course, geographical separation
greatly increases the probability that the two environments are
sufficiently different to allow different selective forces to work in
the two populations.
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