[Aquinasfan]

Now note, none of this is going on in the blink of an eye -- It still takes generations for the genetic differences to render the resulting populations unable to interbreed.

OK, then once again the theory is faced with the problem of the "gappy" fossil record. Where are the countless "micro-transitional" forms?

Another problem remains. According to the theory, at some point one creature in the "daughter population" must mutate sufficiently to become "reproductively isolated" from the "parent population." But at the same time this same creature would become "reproductively isolated" from the rest of the "daughter population," unless another member of the daughter population happened to mutate similarly and simultaneously.

[Junior]

If the fossil record is yielding only one individual in several thousand generations (a conservative estimate, considering the time spans we are dealing with), it is going to appear spotty and gappy. Now, for your second contention -- we are dealing with populations, not individuals. If individuals from the separated populations were to be bred, they'd breed fine for several generations after the split. However, as the genes in the two populations grow more and more divergent, the viability of any offspring decreases (horses and mules are sufficiently diverged that any offspring is rendered sterile, but offspring do result). Eventually, the two populations' genes are so divergent that viable offspring are no longer possible. At no point did any of this divergence require two individuals with the same mutation crop up at the same time -- the genes spread through the entire isolated population over time. And over time the mutations in the two separate render the two populations incompatible.