2.04 – 1.94 million years ago
Two million years ago, there were multiple hominin species in Africa. There was Homo habilis, with a larger brain than any australopithecine, but similar body size and long arms. There was also the recently discovered Australopithecus sediba, with brain not especially large, but maybe reorganized in a human direction, and teeth trending human-wards as well.
There were two robust species that we know of, boisei in east Africa and robustus in southern Africa. The robusts had huge premolars and molars, and enormous jaw muscles running through a large zygomatic arch to attach all the way up to the sagittal crest in the middle of the skull. Gorillas have sagittal crests too, but with them it’s about powerful bites from incisors and canines. You, on the other hand, don’t have a sagittal crest. Your temporalis muscle only runs up to your temple.
The robusts are sometimes given their own genus Paranthropus, other times included in Australopithecus. This reflects uncertainty about their relationships. Did robust morphology evolve once, with both boisei and robustus evolving from aethiopicus? Or did it evolve independently several times, with robustus evolving from Australopithecus africanus in southern Africa?
And remarkably, we now know that three different hominin genera were around not just at the same time and but in the same place, hanging around a South African cave system: Paranthropus robustus, plus Australopithecus africanus (an old-timer, with more than a million year past behind her), plus Homo erectus (a newcomer, with a more than a million year future ahead of her).
Logarithmic History 
