Evolution of Human Life History Patterns
Humans are unique in more ways than simply our large brains, language abilities or two-footed walking. We also differ in our life histories or in the tempo and mode of the lives we live. We occupy the slow lane and have unusually long childhoods and long lifespans, while at the same time weaning our infants early and producing the next offspring in relatively rapid succession. This strange life pattern relates specifically to the energy demands of the large human brain. We know that in modern humans, the rate of body growth in children is at its lowest when the energetic costs of the growing brain are at the highest. The long period of human childhood is therefore the direct energetic result of our large human brains. It also has a number of benefits including, for example, an extended time for childhood learning and the opportunity for early weaning and cooperative childcare that helps reduce the mother’s energetic burden. The question is when this unique life history pattern emerged in human evolution. The fossils provide some clues and suggest that although cooperative childcare may have been present early in the evolution of the genus Homo, the full human life history pattern including both extended childhood growth and development and longevity were much more recent evolutionary developments.