[MalcolmS]

In just a few hundred years, likely no more than a thousand, you can breed every variety of dog, from Chihuahua to Irish Wolf Hound, starting with some common mutts.

I would guess it would take about 16X longer for humans, given the likely age at onset of sexual maturity.

That would be if someone were directing the breeding program. A bit longer if left to themselves with geographic isolation, etc. as the diversity drivers.

[CobaltBlue]

Remember, human beings self-select based on individual preferences.

Researchers testing preferences have overlapped multiple faces of many different races to come up with a "generic" human face, and then tested to see whether this face is more or less attractive than any given human face. Surprisingly, this "average" face is considered quite attractive.

Women are more attracted to "masculine" faces when ovulating.

Human beings are very interesting creatures.