Fission-fusion and the evolution of hominin social systems.

The course of hominin evolution has involved successive migrations towards higher absolute latitudes over the past three million years. Poorer habitat quality further from the equator has led to the necessity for groups occupying higher latitudes to live at lower population densities. Coupled with a trend towards increasing group size over this time period, this tendency towards expansion has led to exponential increases in the area requirements of hominin groups, and a concomitant need to adjust foraging patterns. The current analyses suggest that the development of increasingly complex, multi-level fission-fusion social systems could have freed hominins of the foraging constraints imposed by large group sizes and low population densities. Analyses of the fossil record suggest latitudinally-driven differences in area requirements of the australopithecines from East and South Africa, and African and Asian Homo erectus. In contrast, chronologically-driven differences appear between H. erectus as a whole and Homo heidelbergensis, and between H. heidelbergensis and the Neanderthals. These results are discussed in relation to studies of the foraging patterns of primates and hunter-gatherers.