Environmental complexity, life history, and encephalisation in human evolution

Brain size has increased threefold during the course of human evolution, whilst body weight has approximately doubled. These increases in brain and body size suggest that reproductive (and, therefore, evolutionary) rates must have slowed considerably during this period. During the same period, however, environmental heterogeneity has increased substantially. A central tenet of life-history theory states that in heterogeneous environments, organisms with fast life histories will be favoured. The human lineage, therefore, has proceeded in direct contradiction of this theory. This contribution attempts to resolve this contradiction by recourse to Godfrey-Smith's Environmental Complexity Thesis, which states that the function of cognition is to enable the organism to deal with environmental complexity. It is suggested that among slowly reproducing organisms the behavioural flexibility provided by advanced cognitive abilities is a fundamental component of adaptation to heterogeneous environments. In the human lineage this flexibility is manifest particularly in the increasing complexity of material culture.