Thus we will look at a few major steps in evolution and some of the things affecting human evolution.
Primates are a relatively old order of mammals.
These traits may have played a role in the evolution of brain size in the lineage leading to humans. At least 20 mybp the Hominoids split off from the other old world monkeys. 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.