There is an inherent complexity in any social group. Not only must we remember the individuals who make up the group, we must also remember the relationships between them–and while the number of individuals increases arithmetically, the number of relationships grows exponentially. If we have 99 people, and add 1 more, we’ve only added one individual, but 99 new relationships. It seems that it was precisely that complexity that drove the growth of the primate brain. If that is true, then the seperation from Australopithecine to Homo was likely driven by a social evolution. This is the same time we start to see the first stone tools, and possibly the first evidence for hunting, rather than scavenging. Hierarchical troops make social groups less complex, by fitting all members into a strict hierarchy–chimpanzees can get by simply remembering the individuals and their rank. Rhizomatic societies–that is, egalitarian societies–have an exponential number of relationships, as each individual relates to every other individual in new and different ways. As humans became hunter-gatherers, the simple hierarchical model that served so many other primates ceased to suffice. We needed to become egalitarian to survive, and in order to do that, we needed bigger brains relative to our bodies.