Well the simplest explanation is the classic nature vs. nurture, paired with selective breeding. If you are raised by hippie shroom eating chimp parents, you'll probably be attracted to a different sort of mate than if you are raised in a warrior clan. This sort of taming can happen within 3-4 generations and have permanent effects.
It's not at all clear to me that humans, ancient or modern, are tamer than other great apes. Chimps in particular are notoriously violent (have you ever seen that picture of a shaved ape? That thing could tear you to shreds!), however other great apes are significantly more pleasant. Also modern humans have an incredible capacity for violence, and there is a lot of archeological evidence to suggest that ancient humans did as well.
What takes foxes a number of generations to change, corporations can change in people just by altering incentives. This is the double edged sword of intelligence.
Demonstrating how we can "play god", to some degree, in some circumstances. Kinda makes you wonder if humans might be capable of more than the current state of affairs on this planet.
Dmitry Belyayev was able to produce a tame variety of the red fox within 4 generations of breeding: https://en.wikipedia.org/wiki/Dmitry_Belyayev_(zoologist)#Be...