Question about evolution, genetic bottlenecks, and inbreeding

You're confused because that's not the way evolution works. You're close, but "common ancestor" does not imply individual.Evolution occurs over populations.So, Population A is comprised of 20,000 individuals. Something happens, and that population splits into two daughter populations - Pop. B and C, each with around 10,000 individuals. These two populations, if they do not interbreed, will continue to evolve in divergent pathways. Population B could be the ancestors of humanity, while Population C could be the ancestors of chimpanzees.No inbreeding required.The separation of populations can happen for any number of reasons - natural disasters, migration due to overpopulation, what have you. Edited by Rahvin, : No reason given.

That's a mistaken impression. As I said, evolution happens over populations, not individuals. It's an incredibly slow process that happens by increments of mutations - Species X does not give birth to Species Y. Species Y is a descendant of Species X only after many generations of mutations sufficient to disallow interbreeding between the two.In each generation, the given population is able to interbreed with itself. No familial inbreeding, and no "single individual" common ancestors (Not to say that single individual common ancestors are impossible, simply that this is not typically what happens).

Incorrect. The most recent common ancestor is still the most recent common ancestor species, which is a population. Individuals don't even enter the picture. All of Species Y is not descended from an individual of Species X; Species Y is descended from a population from Species X.