The other key development is hominin brain encephalization. As our extreme encephalization occurs after the onset of bipedalism we can assume that bipedalism was a prerequisite. The increased meat diet of the bipedal H. erectus coincides with increased encephalization. There are a number of theories as to why encephalization occurred. For example, using hands for toolmaking and other complex activities in turn selects for increased encephalization. Environment can also influence adaptation i.e. Hominins with complex ecological behaviours will develop large brains. Lastly, some Paleoanthropologists argue encephalization is driven by social changes. Hominin hunter gatherers, developed cooperative foraging behaviours requiring development of complex