From my college instruction, the basic idea is that a species-evolution can move rapidly under certain conditions.

And from my ongoing study of man?
That’s exactly what happened to sapiens, in a sense. That is-- 50-70Kyrs ago we only numbered ~10k individuals, like the other Great Apes. But then, we exploded out of Africa, and numbered around ~5B sapiens around the globe, when the Neolithic / Agricultural kicked-off.

Those are some crazy, crazy numbers, compared to other mammals.