Yeah, the Khoisan seem to be the FIRST population group to diverge from mainstream homo Sapiens (or was it the other way around?), and IIRC supposedly compose half of humanity by numbers back 100,000-20,000 years ago. It seems Ice Age Central and Southern Africa were the best biome for hunting-gathering humans.

Of course, post-agriculture most humanity lives in (East and South) Asia, except in Cyrus' age where a third of humanity lives in West Asia and Eastern North Africa. Persia ruled 1/3rd of humanity then, the most out of any empire after that. Except perhaps China of some periods

What is meant here is "most divergent" genetics, but that sounds potentially loaded and less nice than "oldest".

See also the genetics of the San people here: https://en.wikipedia.org/wiki/San_people#Genetics