Human evolutionary change has been rapid and extensive; so much so that the genetic similarity and recent divergence between the human and the chimp lineages came as a profound surprise. Three million years ago humans were relatively minor elements of a rich East African mammalian fauna. Since then, our lineage has expanded geographically, demographically and ecologically. Over roughly the same period, our lineage has experienced an explosive increase in co-operation. We are the only large mammal that depends for essential resources on co-operation with non-relatives. Likewise, tool-use. Beginning about 2.5 million years ago, we became obligate technovores, with the pace of innovation picking up over the last 200,000 years. These changes have been accompanied by others in morphology, life history and family organization. We are not what we used to be. Tellingly, this pattern has not been mirrored in other lineages, as it would be if this trajectory had an external cause. So a first framing idea is that human evolutionary change has been self-generated through positive feedback. Specifically: a feedback loop driven by the increasing complexity of human social environments, and by the problems this complexity causes for co-operation management.