> 40k years is between 1000 and 2000 generations. Why would it be unreasonable to think there could be significant genetic drift over that many iterations?

Sure, it looks like there "could be". So what is interesting is the evidence I presented that there hasn't been.

For why, maybe

https://news.ycombinator.com/user?id=dsfyu404ed

explains. Or, with plants and domestic animals, we managed the evolution with directions in mind, but for humans Darwin had less intense objectives.