Pooled Energy Budgets: Resituating Human Energy Allocation Trade-offs

Across taxa, many life-history traits vary as a function of differences in body size. Among primates, including humans, allometric relationships explain many trends in metabolic, growth, reproductive, and mortality rates. But humans also deviate from nonhuman primates with respect to other developmental, reproductive, and parenting characteristics. Broad relationships between life-history traits and body size assume that energy expended in activity (foraging effort) is proportional to body size, and that energy available for growth and reproduction are equivalent. Because human subsistence and parenting are based on food sharing, and cooperation in labor and childrearing, the ways by which energy is acquired and allocated to alternate expenditures are expanded. We present a modification of the general allocation model to include a mechanism for these energy transfers. Our goal is to develop a framework that incorporates this mechanism and can explain the human life-history paradox; that is, slow juvenile growth and rapid reproduction. We suggest that the central characteristics of human subsistence and energy transfer need to be accounted for in order to more fully appreciate human life-history variability.