system structurally and functionally organized around a life history strategy grounded in sociality allied with high-end extractiveness (Deacon, 1997; Kaplan et al., 2000). But the basis for plasticity also resides in reproductive adaptations for biocultural inheritance.

SOCIALITY AND MULTITASKING IN LIFE HISTORY

Life history theory recognizes ecological, cognitive, and behavioral dimensions but does not adequately consider sociality. Humans must belong to social groups to survive and develop and even to reproduce. Human reproduction depends on relationships, and on sharing resources with others.

The Need for Resource Sharing

The design of the species includes an unusually pronounced pattern of asynchronous energy consumption and production (Kaplan, 1997). In foraging societies, over 25 percent of lifetime energy needs is expended by children in the first 15 years, during which time they generate only 5 percent of lifetime energy production (Kaplan et al., 2000). Furthermore, forager women do not produce as much as they consume until the end of their reproductive careers, although they do show a substantial increase in productivity in the second decade. Males, by contrast, sharply escalate production over adolescence to generate a net energy excess by age 20 and produce double their own calorie consumption over most of the next three decades. Among elders, individual production falls below consumption at age 70 in women and age 60 in men (Kaplan, 1994).

In short, among foragers, provisioning of young and subvention of reproductive-age women are necessary because of asynchrony between production and consumption. Early consumption is returned in later adult production that supports children and grandchildren. The social-cognitive fabric that sustains provisioning others and concomitant lagged reciprocity is critical to human life history strategy. Yet life history models include neither social production and consumption nor social costs and benefits.

Sociodynamics, Cognition, and Learning

Sociodynamics create or influence conditions for virtually all aspects of life history—timing of weaning, growth rates and adult body size, timing of maturation and first reproduction, pace and degree of fertility, mortality risk, and so forth. Although humans are highly diverse in their beliefs, values, practices, and resultant human ecologies, they share one important similarity: social relationships universally dominate human experience and shape the material and social worlds that individuals must navigate.



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