Evolution is defined as the changing over time of allele frequencies in the gene pool of organisms. Indivdual organisms do not evolve. Populations of organisms do. When a subgroup of the population becomes isolated from the rest of the population and evolves to the point where its members can no longer interbreed with the members of the main population, speciation has occurred. After many such speciation events occurring from within both the subpopulation and the remainder of the population, it is reasonable that the descendants of these two groups will eventually become very different.
So genetic drift, the imperceptable movement of a jawbone occuring over centuries that results in an organism with no selective advantage over its ancestor, do you define that as evolution? The population changed, but they're still capable of breeding with eachother.
This is an important point. You define evolution in these very stark terms... isolation, inability to interbreed. But evolutionists claim that genetic drift occuring in an intact population, resulting in healthy breeding populations is evolution just the same as freak accidents of nature that isolate groups as in your example.
Sorry, but if individuals do NOT evolve, then there's no way in hell populations of them will!