A possible plausible explanation for why some primates became humans

[Chip (OP)]

https://www.quora.com/Africa-is-considered-the-cradle-of-humanity-as-no-hominid-fossil-dating-back-more-than-2-million-years-has-yet-been-found-outside-the-continent-Why-did-God-or-chance-choose-Africa?ch=10&oid=203456056&share=4c7afd16&srid=3wW4V0&target_type=question

Africa is considered the “cradle of humanity”, as no hominid fossil dating back more than 2 million years has yet been found outside the continent. Why did God or chance choose Africa?

What we think happened is that the cosmic radiation from a nearby supernova triggered a rush of electrical storms which burned off a lot of dry brush in Africa, opening up new savannah, and the population of our last common ancestor with the chimps, an already semi-bipedal ape, split.

One lot retreated into deeper jungle, went back down on all fours and evolved into chimps and bonobos whilst the other lot moved out into the savannah where they became more bi-pedal because it was useful to be able to see long distances across the open plains.

That freed up their hands to become more dexterous, so they could make better tools, and being able to make better tools made it worthwhile spending the energy to run bigger brains.

If it had happened in Asia instead, and fully sapient apes had evolved from a recent common ancestor with the orangutans, we would probably have been a lot nicer.