The first humans would have been the survivors and thrivers in the long-established pre-human enviroment from which they arose. That wouldn't have been easy an

The first humans would have been the survivors and thrivers in the long-established pre-human enviroment from which they arose. That wouldn't have been easy and the incredible amount of time it would take can be calculated but is still difficult to fathom. Seems like "survival of the fittest" could have been very fitting at the time, and there would be insignificant diversity in genetics and culture to begin with, compared to today. Once humans come along, then starts another huge period of gradual change in humanity itself. What could lead to greater diversity than gradual isolation of cultures in highly disparate environments for incredible amounts of time? Especially when humans are self-selecting for environment and culture more so than other earthlings by orders of magnitude. And time can do so much.