The dates are rough and get changed now and then. These both seem to increase noticeably about 2 mybp. One theme that involves each of the different sequences of evolution is that there was some feedback that lead to the increase in cranial capacity, e.g., becoming bipedal creates selection pressure for a more elaborate brain to control motor function and to process incoming sensory information. This in turn would allow for more successful bipedalism, etc. The same argument could be leveled about culture leading to an increase in brain size, and vice versa, so the sequence cannot be resolved just on the logic of feedback loops alone.
Paleontological evidence suggests a single origin in Africa .
Molecular data shows low genetic diversity worldwide with the highest diversity in Africa, aslo suggsting an African origin. Recent re-analyses shown that the cladograms of mtDNA cannot support an African origin on statistical grounds. Moreover, some recent fossil finds have put humans outside Africa about 2.4 MYBP, but these may be due to early migrations. The analysis of the evolution of culture and civilization in humans clearly must be based in materials other than human bones alone. The spread of Homo out of Africa is presumed to have taken place about 1.5 MYBP by Homo erectus .