Offspring Human Fertility Behavior in Biodemographic Perspective (2003) / Chapter Skim
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10. Energetics, Sociality, and Human Reproduction: Life History Theory in Real Life
10. Energetics, Sociality, and Human Reproduction: Life History Theory in Real Life
Pages 289-321
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From page 289... ...
This essay attempts to develop a fresh view of human fertility behavior and family formation by considering the intersection of three approacheslife history theory, behavioral and reproductive ecology, and developmental psychobiology. On the theoretical front, life history theory aims to integrate comparative, cross-taxonomic data into a framework comprising life course attributes such as the timing, pace, and forms of reproduction and reproductive effort.
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From page 290... ...
This bold proposition that human behavior has been shaped by selective pressures to optimize fitness inspired a wave of empirical research, the best of which sought to test the validity of this claim and probe its ability to illuminate human behavior. This research builds on an older foundation of evolutionary biology to assess whether and how adaptive design may explain the inter- and intrapopulation variations in human reproductive function.
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From page 291... ...
Using this insight, evolutionary models, reformulated as biocultural inheritance models, could build in developmental psychobiology to provide a more complete picture of human reproductive behavior that incorporates social viability as a goal for offspring, an absolute prerequisite for successful human reproduction. The analysis here begins with an examination of life history design, particularly resource allocation over the life course to growth, reproduction, and maintenance, as effected through neuroendocrine-endocrine regulators (abbreviated as neuro-endocrine)
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LIFE HISTORY THEORY AND ENERGETICS Life history theory concerns the evolved design constraints that shape species-specific phenotypes across the life course and that underlie the striking contrasts in life histories across the animal kingdom and even within taxa. Theorists seek design features from comparative evolutionary biology that will explain fertility and mortality schedules classic demographic concerns.
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. The acquisition and the disposition of resources are both components of life history strategy, but current life history theory attends little to the input or acquisition side (a focus of behavioral ecology; Smith and Winterhalder, 1992~.
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; sex determination and the relative contributions ot males and females to reproduction; and the slope of reproductive value with age. Evolutionary analysis has focused, virtually from its inception, on the necessary reproductive effort (Darwin 1871; Maynard Smith, 1978; Trivers, 1972; Williams, 1985)
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but required for attaining adult competence. Human Life History Strategy Humans are large, long lived, and obligately social primates that have altricial singleton births, spaced at 2 to 5 years, which are first breastied and then provisioned well into the second decade.
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Challenges for Life History Theory Life history theory has excited interest because it applies formal and game theoretical models to comparative data; provides a life span, timeintegrated framework; integrates across components of phenotype rather than focusing on specific features; identifies key cost-benefit trade-offs in the design of life history strategies; and thus suggests organic design criteria and evolutionary constraints. It promises to be generalizable, predictive, and hypothesis generating.
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From page 297... ...
The following sections bring the strengths of life history analysis to bear on human fertility behavior while addressing limitations and expanding the scope of adaptationist thinking to substantially strengthen the analytic purchase on human reproduction. TRANSLATION AND TRANSMISSION OF EVOLVED DESIGN An integrated theory of reproductive ecology requires linkage of life history theory with phenotype and the mechanisms that produce life history, particularly reproductive careers.
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. At this point, limitations on the applicability of life history theory to intraspecific variations become clear, for life history predicts that adult mortality risk will be associated with earlier onset of the reproductive career (Charnov, 1993~.
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Two Mediating Mechanisms Phenotypic variations in reproductive behavior, such as variations in the timing of puberty, must originate somehow from evolved life history design. Two issues are involved, and lead to two distinctive but ultimately related sets of mediating mechanisms.
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Endocrine Architecture of Life History Physiological mechanisms for producing life history phenotypes remain unspecified in life history theory, but neuroendocrine-endocrine (or neuroendocrine) systems are obvious candidates (Finch and Rose, 1995~.
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axis, which regulates gonadal function, including output of gonadal steroids (estradiol, E2; testosterone, T) , which are responsible for reproductive functions and behaviors and many sex differences; (3)
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This brief survey of endocrine architecture reveals that life history parameters have demonstrable physiological bases and furthermore raises several points about neuro-endocrine function. First, neuro-endocrine activity can be seen as clearly aimed at allocating resources among the domains of growth, reproduction, and maintenance.
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. Biocultural Inheritance and Fertility Behavior The problem of intergenerational transmission for reproduction in the fullest, phenotypic, life history sense has concerned Western biologists and
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Such integration sheds a different light on human reproduction and the selective pressures on it. If human development is coextensive with fertility in determining successful reproduction, the proximate determinants of fertility will require significant expansion to account for effective fertility, that is, for successful transmission of not only genotype but also biocultural patterns.
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From page 305... ...
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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From page 306... ...
Performances of social reciprocity (e.g., conversation) are crucial to form and maintain social relationships in the short term and long term, and require integrated use of memory, signal processing, social intelligence, empathy, emotion processing, and behavior production (language, expression, gesture)
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From page 307... ...
On the one hand are the tangible resources emphasized in life history analysis that constitute material capital: food, shelter, safety, labor, and mates. On the other hand are immaterial resources largely overlooked in life history theory and that comprise social capital: information, social connections and memberships, social support and opportunity, assistance and cooperation, coordination and triage, and economies of scale.
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Hence, social costs and benefits should be included in the energy calculus of life history theory. The Costs of Sociality Sociality requires energy and exacts costs that alter the calculus of resource allocation.
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Indeed, the differential reproductive burden imposed by types of labor may relate to their compatibility with multitasking (as with the Hadza, in Hawkes et al., 19971. Among Hadza foragers, for example, the value of granumaternai care tor easing a daughter's reproductive effort emerges as significant only in seasons when a mother's foraging involves tasks incompatible with concurrent child care.
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The ubiquity of multitasking relating to reproduction and involving social life indicates that its omission may limit the capacity of current behavioral ecology and life history theory to contribute to the understanding of human reproductive behavior. The importance of social relationships, their role in fertility behavior, and their value in determining long-term offspring viability are not unique to humans.
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. 1 J enough information to specify phenotype in its myriad details; indeed, initial human genome maps reported in 2001 gauge the number of proteincoding genes at 30,000 to 40,000 (International Human Genome Sequencing Consortium, 2001; Venter et al., 2001)
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are far more subtle than immediate ecological and cumulative sociocultural effects (Chisholm, 1993, 1996; Hill and Hurtado, 1995~. IMPLICATIONS FOR RESEARCH AND POLICY The view of human reproduction as rooted in biocultural inheritance casts new light on current human affairs.
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We can expect a large measure of robustness in biocultural transmission for critical features such as language and for those under previous selection for retention of plasticity. Other areas of human developmental ecology may be more vulnerable, particularly (1 )
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These formidable challenges raise the bar for effective theory that will support new hypotheses about human behavior, stimulate research, and inform policy. Pushing past dual thinking about the human condition and operationalizing biocultural inheritance models may provide the start to understanding the human implications of these challenges.
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Pp. 339-374 in Evolutionary Ecology and Human Behavior.
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1993 Death, hope, and sex Life history theory and the development of reproductive strategies. Current AntI7ropology 34:1-24.
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1994 Advances in human reproductive ecology. Annual Review of Anthropology 23 :255-275.
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Human Nature 6:325-360. The evolution of the human life course.
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Promislow, D., and P.H. Harvey 1990 Living fast and dying young: A comparative analysis of life history variation among mammals.
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Winterhalder, eds. 1992 Evolutionary Ecology and Human Behavior.
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From page 321... ...
Wood, J.W. 1994 Dynamics of Human Reproduction.
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