. "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
bioinformatics challenge that cannot have a purely organic solution but must be seen as a problem of biocultural inheritance.
The following sections explore these two set of reproductive mechanisms—endocrine architecture for translating life history design into phenotype and biocultural inheritance for transmitting information to instruct translation.
Endocrine Architecture of Life History
Physiological mechanisms for producing life history phenotypes remain unspecified in life history theory, but neuroendocrine-endocrine (or neuro-endocrine) systems are obvious candidates (Finch and Rose, 1995). Hormones act like pacemakers for growth and developmental transitions. They are responsible for establishing the prolonged juvenile period in humans and govern the timing of puberty and the progression to reproductive maturity. Neuro-endocrine action thereafter orchestrates adult reproductive function, including the production of gametes, establishment and course of pregnancy, parturition, lactation, reproductive aging, and menopause.
The large array of neuro-endocrine regulatory systems handles resource partitioning among growth, reproduction, and maintenance. Interactions across this array determine productivity and negotiate resource allocation to short- and long-term life history projects, balancing the immediate demands of survival (e.g., metabolism, immune function) against long-term needs for growth or reproduction.
For instance, neuro-endocrine responses to psychosocial distress antagonize gonadal activity, for such distress arises from conditions likely to be less favorable for reproduction. Moreover, psychological distress and poor nutritional state each reduce sexual interest, and thereby dampen reproduction by both physiologic and behavioral routes. Hence, hormones mediate the interface between individual and environment, effecting triage to meet shifting demands and exigencies. They also present the means for facultative adjustment of life history parameters, mediating for instance the relationship of maternal workload to duration of postpartum amenorrhea.
Figure 10-3 presents the principal endocrine regulatory pathways that mediate energy allocation and trade-offs among growth, reproduction, and maintenance (reviewed in Worthman, 1999b, 2002). All these pathways traffic between brain and periphery, and four of them run from the hypothalamus at the floor of the brain, which regulates pituitary activity by releasing hormones or inhibitory factors (CRH, GnRH, etc.). Hypothalamic-releasing hormones stimulate or suppress pituitary output of trophic hormones (ACTH, LH/FSH, etc.) that act on target glands in the periphery (adrenals, gonads, etc.). In turn, target glands release hormones that mediate the stress response, reproductive function and behavior, growth, and metabolism.