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Human Life History (human + life_history)
Selected AbstractsPooled energy budget and human life historyAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Meredith W. Reiches Human life history contains a series of paradoxes not easily explained by classical life history theory. Although overall reproductive output is higher than in related primates, juvenile growth is slower and age-specific reproductive rates decline faster with age. A simple energetic model would predict that growth and reproductive rates should be positively correlated and that reproductive effort should not decelerate with age. The pattern of negative correlations in humans suggest the presence of trade-offs among peak reproductive rate, childhood growth, and reproductive rate at older ages. To address this puzzle, we propose a synthesis of reproductive ecology and behavioral ecology focused on intra- and inter-somatic energy transfers. This integration includes three concepts: the mother as final common pathway through which energy must pass to result in offspring; a distinction between direct and indirect reproductive effort, proposing the latter as a novel net energy allocation category relative to growth and direct reproductive effort; and a pooled energy budget representing the energetic contributions and withdrawals of all members of a breeding community. Individuals at all reproductive life stages are considered in light of their contributions to the pooled energy budget. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Early reproductive maturity among Pumé foragers: Implications of a pooled energy model to fast life historiesAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Karen L. Kramer Life history theory places central importance on relationships between ontogeny, reproduction, and mortality. Fast human life histories have been theoretically and empirically associated with high mortality regimes. This relationship, however, poses an unanswered question about energy allocation. In epidemiologically stressful environments, a greater proportion of energy is allocated to immune function. If growth and maintenance are competing energetic expenditures, less energy should be available for growth, and the mechanism to sustain rapid maturation remains unclear. The human pattern of extended juvenile provisioning and resource sharing may provide an important source of variation in energy availability not predicted by tradeoff models that assume independence at weaning. We consider a group of South American foragers to evaluate the effects that pooled energy budgets may have on early reproduction. Despite growing up in an environment with distinct seasonal under-nutrition, harsh epidemiological conditions, and no health care, Pumé girls mature quickly and initiate childbearing in their midteens. Pooled energy budgets compensate for the low productivity of girls not only through direct food transfers but importantly by reducing energy they would otherwise expend in foraging activities to meet metabolic requirements. We suggest that pooled energy budgets affect energy availability at both extrinsic and intrinsic levels. Because energy budgets are pooled, Pumé girls and young women are buffered from environmental downturns and can maximize energy allocated to growth completion and initiate reproduction earlier than a traditional bound-energy model would predict. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Pooled energy budget and human life historyAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Meredith W. Reiches Human life history contains a series of paradoxes not easily explained by classical life history theory. Although overall reproductive output is higher than in related primates, juvenile growth is slower and age-specific reproductive rates decline faster with age. A simple energetic model would predict that growth and reproductive rates should be positively correlated and that reproductive effort should not decelerate with age. The pattern of negative correlations in humans suggest the presence of trade-offs among peak reproductive rate, childhood growth, and reproductive rate at older ages. To address this puzzle, we propose a synthesis of reproductive ecology and behavioral ecology focused on intra- and inter-somatic energy transfers. This integration includes three concepts: the mother as final common pathway through which energy must pass to result in offspring; a distinction between direct and indirect reproductive effort, proposing the latter as a novel net energy allocation category relative to growth and direct reproductive effort; and a pooled energy budget representing the energetic contributions and withdrawals of all members of a breeding community. Individuals at all reproductive life stages are considered in light of their contributions to the pooled energy budget. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Childhood, adolescence, and longevity: A multilevel model of the evolution of reserve capacity in human life historyAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Barry Bogin The grandmother hypothesis (GH) of Hawkes et al. ([1998]: Proc Natl Acad Sci USA 95: 1336,1339) finds that selection for lower adult mortality and greater longevity allow for the evolution of prolonged growth in human beings. In contrast, other researchers propose that the evolution of the human childhood and adolescent stages of life history prolonged the growth period and allowed for greater biological resilience and longevity compared with apes. In this article, the GH model is reanalyzed using new values for some of its key variables. The original GH set the age at human feeding independence at 2.8 years of age (weaning) and used demographic data from living foragers to estimate average adult lifespan after first birth at 32.9 years. The reanalysis of the GH uses age 7.0 years (end of the childhood stage) as the minimum for human feeding independence and uses data from healthier populations, rather than foragers, to derive an estimate of 48.9 years for average adult life span. Doing so finds that selection operated to first shorten the infancy stage (wean early compared with apes), then prolong the growth period, and finally result in greater longevity. The reanalysis provides a test of the reserve capacity hypothesis as part of a multilevel model of human life history evolution. Am. J. Hum. Biol. 2009. © 2009 Wiley-Liss, Inc. [source] Antiquity of postreproductive life: Are there modern impacts on hunter-gatherer postreproductive life spans?AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2002Nicholas G. Blurton Jones Female postreproductive life is a striking feature of human life history and there have been several recent attempts to account for its evolution. But archaeologists estimate that in the past, few individuals lived many postreproductive years. Is postreproductive life a phenotypic outcome of modern conditions, needing no evolutionary account? This article assesses effects of the modern world on hunter-gatherer adult mortality, with special reference to the Hadza. Evidence suggests that such effects are not sufficient to deny the existence of substantial life expectancy at the end of the childbearing career. Data from contemporary hunter-gatherers (Ache, !Kung, Hadza) match longevity extrapolated from regressions of lifespan on body and brain weight. Twenty or so vigorous years between the end of reproduction and the onset of significant senescence does require an explanation. Am. J. Hum. Biol. 14:184,205, 2002. © 2002 Wiley-Liss, Inc. [source] Brief communication: Evaluating grandmother effectsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009Kristen Hawkes Abstract Women who have outlived child-bearing have long been described as postreproductive. But contributions they make to the survival or fertility of their descendants enhance the reproduction of their genes. Consequently, natural selection affects this characteristic stage of human life history. Grandmother effects can be measured in data sets that include births and deaths over several generations, but unmeasured covariates complicate the task. Here we focus on two complications: cohort shifts in mortality and fertility, and maternal age at death. We use the Utah Population Database to show that longevity of grandmothers may be associated with fewer grandchildren, as reported by Madrigal and Melendez-Obando (Am J Phys Anthropol 136 (2008) 223,229) for a Costa Rican sample, even when grandmother effects are actually positive. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] The evolution of human life history , Edited by Kristen Hawkes & Richard R. PaineTHE JOURNAL OF THE ROYAL ANTHROPOLOGICAL INSTITUTE, Issue 3 2008Chris Knight [source] | ||||||||||