That is not speculation. That is a fact. If your faith were dependent upon that being a “myth” it seems your faith is fragile.
Genetic changes within a population are the only thing that DO result in changes in morphology of a population.
What do YOU suppose determines our inherited morphology if not our DNA?
Besides, my question didn't ask about “additional morphology”, I asked about fertility between populations. Fertility between populations IS based upon DNA similarity, in case you were wondering and that was going to be your next wrong answer.
Here is the question again, in case you want to take another stab at it....
“What would preclude two separate populations of the same species from accumulating enough differences in DNA over time that they could no longer reproduce between groups after sufficient time and the accompanying INEVITABLE change in DNA?”
“Genetic changes within a population are the only thing that DO result in changes in morphology of a population.”
Seems to me, that one’s a bit off.
I’m no expert on feral pigs (outside the realm of my crosshairs), but let’s take a look at them. Longer snouts, bigger tusks induced by change in environment.
“What would preclude two separate populations of the same species from accumulating enough differences in DNA over time that they could no longer reproduce between groups after sufficient time and the accompanying INEVITABLE change in DNA?”
The question contains the same error as that which asks: “What would preclude a very large number of chimpanzees from typing out the complete works of Shakespeare, if we just provide them with enough time and typewriters?”
The error is failing to understand that (observable) objects and events in the real world are not unrestrained by space and time in the way mathematical calculations are.
To answer your question, the list of preclusions would be almost without end.