. "10. Energetics, Sociality, and Human Reproduction: Life History Theory in Real Life." Offspring: Human Fertility Behavior in Biodemographic Perspective. Washington, DC: The National Academies Press, 2003.
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Offspring: Human Fertility Behavior in Biodemographic Perspective
ways are organized to reflect the nature of life history demands, as in the contrast between the centrally regulated, clearly localized operation in reproduction versus the decentralized, distributive organization of the immune system. Potentially expensive and risky reproductive behaviors are under high selective pressure for appropriate timing, prolonged reallocation of resources, maintenance of biological states (cyclicity, pregnancy, parturition), and target orientation (e.g., placental [i.e., fetal] regulation of pregnancy, lactation dependence on infant stimuli).
Second, contrary to the classic silo model of endocrine organization reflected in the vertical pathways of Figure 10-3, each axis demonstrates systematic cross-talk. Cross-talk is understood rather differently when viewed from a life history perspective that throws into relief the necessity for mechanisms to allocate and reallocate energetic resources. Cross-talk provides the means to reallocate energy and modulate axis activity to meet ongoing relative demands and to do so in a physiologically integrated and synchronized manner.
Third, the neuro-endocrine architecture of life history not only supports biological functions comprising reproduction, growth, and maintenance but also integrally involves cognition and behavior. This involvement runs both ways: Hormones directly inform affect and behavior, as exemplified in the operation of the adiposal axis and the immune system, but behavior and cognition also influence hormones, as most directly exemplified by the HPA axis (McEwen, 2000; Seeman and McEwen, 1996). Such mechanisms coordinate the endocrine with the behavioral architectures of life history, as reflected in the functions of the brain as a primary site for experiential processing and memory, a center for physiological regulation and integration, and a target of peripheral modulation and signaling through endocrine action.
Fourth, the timing and course of life history events depend on ecological signals of environmental quality. Neuro-endocrine mechanisms transduce this information into physiological responses over the short term and long term. In the case of humans, favorable ecological circumstances include energetic conditions that are at least permissive, which are signaled by hormones like leptin, insulin, or cytokines, as well as positive social conditions, which are indexed through central processing (cognition and memory), emotion systems, and the HPA. These systems embody the individual’s knowledge of the surrounding social ecology (a formulation analogous to Kaplan’s  notion of embodied capital).
Biocultural Inheritance and Fertility Behavior
The problem of intergenerational transmission for reproduction in the fullest, phenotypic, life history sense has concerned Western biologists and