Population Age Structure

Humans have notably older population age structures than the other great apes. This reflects the later ages at first birth and lower adult mortality rates of our species. The wider range of ages in human families and communities increases the diversity of both potential allies and competitors, and affects social strategies for success. Young men face not only others like themselves in mating competition, but also older men who are well ahead of them in establishing their own social position. Since humans differ from other primates in the extent to which food is shared, the economic productivity of community members affects both their own consumption and the resource consumption of others. Unlike other apes, and most other primates, human males produce substantial proportions of the food consumed others, not only their own wives and children. Men’s productivity as well as production from juveniles and women past their age at last birth, can have large effects on lineage growth rates. Provisioning of grandchildren by ancestral females whose own fertility was declining may have favored increased longevity in those lineages, shifting age structures from an ancestral great ape pattern toward the one found in modern humans. Grandmother effects on survival and fertility have been found in many ethnographic and historical populations.