[Potowmack]

No, it wouldn't, because there are many modes of speciation which work just fine even with populations that are "always in contact".

How would that work? If a population of critters is always more or less one group with no geographic borders separating them into sub-groups, how would speciation occur?

After all, wouldn't any mutations in the population spread throughout the population?

Now, the population might evolve, as a whole, from Species A to Species B over a long period. However, unless the population is separated into subgroups, I don't see how you could end up with two different species at the end of this period.

[ahayes]

http://www.evowiki.org/index.php/Theory_of_Evolution#Sympatric_speciation

This gives a very short summary of only a few mechanisms.