Six million years ago a couple in Africa had two sons and their names were Cain and .... Let me try that again.

Six million or so years ago there was a population of apes living in Africa who shared a lot of DNA (like 99%) with their surviving descendants, chimpanzees, bonobos and humans.  They probably looked a lot like those descendants, had brains about like chimps, were hairy like chimps and gorillas, and walked like them, but we really don't know because there is no trace of them in the fossil record.  Some of their offspring became chimps and bonobos, but we don't know much about their evolution since they didn't leave any trace in the fossil record for another 5 plus million years.  Other branches did start leaving traces a couple of millions of years later and they tend to be chimp sized, with chimp sized brains, but may have walked slightly more like humans.

By about three million years ago some definitely upright walkers appeared.  They were still about chimp size, very short, and had brains only slightly larger than  those of chimps, but around two million years ago they, or somebody, does appear to have made simple tools from rocks.  They shared perhaps the central human trait, an obligatory upright gait, but we really don't know if they were ancestral to us, but either they or some fellow upright walkers were.

About two million years ago, at the roughly the same time the chimps and bonobos were splitting from each other, the first definitely ancestral creatures appeared.  They were now much taller, our size, walked like us, and had brains more than twice as large as chimp brains, in fact only slightly smaller than ours.  They, Homo erectus, seem to have been the first humans to have gotten out of Africa, and after doing so spread over much of Eurasia.  They had learned to make simple hand axes, a technology that evolved very slowly over the next million and a half years.

They seemed to have evolved rather slowly over the next million years or so into several separate species, one of which split into Neandertal, Denisovan, and the ancestors of modern humans half a million or more years ago.  Anatomically modern human first appear in the African fossil record 200 or 300 kilo years ago (kya).  Evidence of modern behavioral traits (art and jewelry) didn't come until 60 or so kya.  About that time our ancestors left Africa again and outcompeted or exterminated all the other human species over the next 30,000 years or so.


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