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An Evolutionary and Ecological Analysis of Human Fertility, Mating Patterns, and Parental Investment

Hillard S. Kaplan and Jane B. Lancaster

This chapter considers the evolutionary biology of human fertility, parental investment, and mating and is designed to provide a broad overview of the topic. It focuses on three themes. The first is the timing of life events, including development, reproduction, and aging. Second is the regulation of reproductive rates and its relationship to parental investment. Sexual dimorphism and its relationship to mating systems together are the third theme. Each of these themes is addressed from two perspectives: first, in a comparative cross-species context, and second, in terms of variation within and among human groups. Our primary goal is to introduce a new ecological framework for understanding variations in each of those domains and then to apply the framework to understanding both the special characteristics of our species in a comparative perspective and variations within and among human groups. A secondary goal is to discuss how evolutionary biology can be integrated with more traditional approaches to human demography and the new research questions such integration would generate.

The first section of this chapter presents an introduction to life history theory and current thinking in evolutionary biology with respect to the three themes. Since the fitness consequences of alternative fertility and parental investment regimes depend on ecology and individual condition, both specialization and flexibility in life histories are considered. Building on this foundation, an ecological framework for understanding variation in each of those domains is then introduced. The second section discusses humans in a comparative context, with a particular emphasis on the hunter-and gatherer lifestyle because of its relevance to the vast majority of human



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Offspring: Human Fertility Behavior in Biodemographic Perspective 7 An Evolutionary and Ecological Analysis of Human Fertility, Mating Patterns, and Parental Investment Hillard S. Kaplan and Jane B. Lancaster This chapter considers the evolutionary biology of human fertility, parental investment, and mating and is designed to provide a broad overview of the topic. It focuses on three themes. The first is the timing of life events, including development, reproduction, and aging. Second is the regulation of reproductive rates and its relationship to parental investment. Sexual dimorphism and its relationship to mating systems together are the third theme. Each of these themes is addressed from two perspectives: first, in a comparative cross-species context, and second, in terms of variation within and among human groups. Our primary goal is to introduce a new ecological framework for understanding variations in each of those domains and then to apply the framework to understanding both the special characteristics of our species in a comparative perspective and variations within and among human groups. A secondary goal is to discuss how evolutionary biology can be integrated with more traditional approaches to human demography and the new research questions such integration would generate. The first section of this chapter presents an introduction to life history theory and current thinking in evolutionary biology with respect to the three themes. Since the fitness consequences of alternative fertility and parental investment regimes depend on ecology and individual condition, both specialization and flexibility in life histories are considered. Building on this foundation, an ecological framework for understanding variation in each of those domains is then introduced. The second section discusses humans in a comparative context, with a particular emphasis on the hunter-and gatherer lifestyle because of its relevance to the vast majority of human

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Offspring: Human Fertility Behavior in Biodemographic Perspective evolutionary history. The third section applies the framework developed in the first two parts to understanding major historical trends in human fertility, parental investment, and mating regimes. The transition from hunting and gathering to farming and pastoralism is considered first. Land- and power-based stratified societies are then discussed, followed by an analysis of wage-based competitive labor markets and demographic transition. The chapter concludes with a discussion of the new research questions and approaches to research design suggested by this framework. THE THEORETICAL FRAMEWORK Fundamental Trade-Offs in Life History Theory Natural selection acts on variability in the traits of individual organisms within populations. Traits (and the genes that code for them) increase in frequency relative to other traits when their average effects on the individuals possessing those traits act to maximize their long-term production of descendents through time.1 Fertility is the most direct contributor to an organism’s fitness (i.e., the number of descendents it produces). In fact, all other fitness components, such as mortality, only affect fitness through their effects on fertility (e.g., mortality rates affect fitness by affecting the probability of living to the next reproductive event). All else constant, any increase in fertility increases an organism’s fitness. However, there are two trade-offs affecting natural selection on fertility. The first is the trade-off between present and future reproduction. An organism can increase its energy capture rates in the future by growing and thus increasing its future fertility. For this reason, organisms typically have a juvenile phase in which fertility is zero until they reach a size at which some allocation to reproduction increases fitness more than growth. Similarly, among organisms that engage in repeated bouts of reproduction (humans included), some energy during the reproductive phase is diverted away from reproduction and allocated to maintenance so that it can live to reproduce again. The general expectation is that natural selection on age of first reproduction and on the adult reproductive rate will tend to maximize total allocations of energy to reproduction over the life course. 1   Selection acts on the “inclusive fitness” of genes coding for traits. Inclusive fitness includes effects on both the reproductive success of the individual bearing the gene and other individuals, related by common descent, who also bear the gene. For example, selection on genes affecting alarm calls in response to predators depends both on their effects on the reproductive fitness of the caller (who may risk a greater threat of predation) and on relatives bearing those genes (whose lives may be saved by the call).

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Offspring: Human Fertility Behavior in Biodemographic Perspective The second trade-off is between quantity and quality of offspring, where quality is a function of parental investment in offspring and reflects its ability to survive and reproduce. The general expectation is that natural selection on offspring number and investment per offspring will tend to maximize the long-term production of descendents; this may be estimated by the number of offspring that survive to reproduce themselves during an organism’s lifetime (Smith and Fretwell, 1974) or if fertility affects the production and survival of grandchildren, by more distant effects. Sexual reproduction, which most probably evolved as a means of increasing variability among offspring through the sharing of parents’ genetic material, complicates the trade-off between quantity and quality of offspring. This is because offspring share roughly equal amounts of their parents’ genetic material, yet parents may contribute unequally to their viability. In this sense, offspring may be considered as “public goods,” with each parent profiting from the investments of the other and having an incentive to divert resources to the production of additional offspring. This public goods problem tends to create conflicts of interest between the sexes (see Gangestad, this volume, for a treatment of such conflicts). In fact, an almost universal by-product of sexual reproduction is the divergent evolution of the two sexes. Sex is defined by gamete size, and the sex with the larger gametes is called female. Larger gametes represent greater initial energetic investment in offspring. With increased investment beyond energy in gametes, the divergence between the two sexes is often exaggerated but may also balance or even reverse. For example, females provide all investment to offspring in greater than 95 percent of mammalian species, but males provide similar amounts or more total investments among most altricial birds, male brooding fish, and some insects, such as katydids (see Clutton-Brock and Parker, 1992, for a review). To the extent that one sex invests more in offspring than the other, the one that does more investing sex is in short supply resulting in operational sex ratios greater than unity and competition for mates among members of the sex that does less investing. This public goods problem generates the third major trade-off: that between mating and parental effort. Sexual reproduction involves two components: finding a mate and achieving a mating, on the one hand, and investing in the resulting offspring to increase its viability, on the other. To the extent that there are gains from specialization in the two components, one sex will evolve to produce many small highly mobile gametes specialized to mating, and another will evolve to produce fewer larger gametes, specialized for energetic investments in offspring. Trivers (1972) recognized that these differences in relative parental investment affect the structure of mating markets and the characteristics of the more and less investing sexes. The more investing sex is selected to be choosy about when

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Offspring: Human Fertility Behavior in Biodemographic Perspective and with whom to mate, and the less investing sex is selected to possess characteristics that increase its mating opportunities. This leads to what economists call negative externalities, since male resources are wasted on costly displays or handicaps (Grafen, 1991) or on fighting, rather than in offspring production. The general expectation is that natural selection acts on mating and parenting effort in populations of males and females so that individual fitness tends to maximize in a competitive equilibrium (i.e., it tends to generate distributions of mating and parenting effort among males and females that cannot be “invaded” by alternative distributions). Ecology and Life History Evolution Variations across taxa and across conditions in optimal energy allocations and optimal life histories are shaped by ecological factors, such as food supply, mortality hazards, and the effects of body size on both energy capture and mortality hazards (Charnov, 1993; Kozlowski and Weigert, 1987; Werner, 1986). It is generally recognized that there are species-level specializations that result in bundles of life history characteristics, which, in turn, can be arrayed on a fast-slow continuum (Promislow and Harvey, 1990). For example, among mammals, species on the fast end exhibit short gestation times, early reproduction, small body size, large litters, and high mortality rates, with species on the slow end having opposite characteristics. It is also recognized that many, if not most, organisms are capable of slowing down or speeding up their life histories, depending on environmental conditions such as temperature, rainfall, food availability, density of conspecifics, and mortality hazards. Within-species variation in life history characteristics can operate over several different timescales. For example, there is abundant evidence that allocations to reproduction, as measured by fecundity and fertility, vary over the short term in relationship to food supply and energetic output among plants, birds, and humans (Hurtado and Hill, 1990; Lack, 1968). Extensive research on many bird species has shown that this phenotypic plasticity tracks fitness quite well (Godfray et al., 1991). Birds under variable conditions adjust clutch sizes in ways that tend to maximize the number of surviving young produced during the life course. The impact of the environment may operate over longer time intervals through developmental effects (Lummaa and Clutton-Brock, 2002). For example, calorie restriction of rats at young ages tends to slow down growth rates and leads to short adult stature, even when food becomes abundant later in the juvenile period (Shanley and Kirkwood, 2000). Some intraspecific variation operates at even longer timescales, mediated through differential selection on genetic variants in different habitats. For example, rates of senescence vary across different populations of grass-

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Offspring: Human Fertility Behavior in Biodemographic Perspective hoppers, with those at higher altitudes and earlier winters senescing faster than those at lower altitudes as a result of differential selection on genotypes (Tatar et al., 1997). Similarly, there is a great deal of evidence suggesting that male and female parental investments vary in relation to local ecology over both the short run and the long run (see Clutton-Brock and Parker, 1992 for a review). For example, among katydids, males provide females with a “nuptial gift” (a bolus of condensed food energy) to support offspring production. Experimental manipulation of food density, affecting the foraging time necessary for males to produce the food package, produces shifts in male and female mating effort. When the food supply is low, male inputs into reproduction require more time than female inputs, males are in short supply, and females actively compete for males; as food density increases, this trend is reversed and males compete for access to females (Clutton-Brock, 1991; Gwyne, 1991; Gwyne and Simmons, 1990). This mix of specialization and flexibility is fundamental to understanding human life histories and mating systems. On the one hand, it is generally agreed that the large human brain supports the ability to respond flexibly to environmental variation and to learn culturally. This suggests that humans may be most capable of short-term flexibility in the timing of life events and investment strategies. On the other hand, the commitment to a large brain and the long period of development and exposure to environmental information necessary to make it fully functional place important constraints on the flexibility of the human life course and require specializations for a slow life history. In fact, consideration of brain- and learning-intensive human adaptation reveals shortcomings in existing biological theory and inspires the development of a more general approach to life history evolution, which is the focus next. An Evolutionary Economic Framework A general explanatory framework for understanding our species must be able to account for both its distinctive features when compared to other species and the enormous range of variation exhibited by humans under different conditions, in different societies, and at different points in time. To account for these evolutionary trends, we have expanded existing models of life history evolution by explicitly modeling the three trade-offs discussed above using capital investment theory (Becker, 1975; Kaplan, 1996; Kaplan and Robson, 2002; Robson and Kaplan, 2003). The processes of growth, development, and maintenance are treated as investments in stocks of somatic or embodied capital. In a physical sense, embodied capital is organized somatic tissue—muscles, digestive organs, brains, and so forth. In

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Offspring: Human Fertility Behavior in Biodemographic Perspective a functional sense, embodied capital includes strength, speed, immune function, skill, knowledge, and other abilities. Since such stocks tend to depreciate with time, allocations to maintenance can also be seen as investments in embodied capital. Thus, the present-future reproductive trade-off can be understood in terms of optimal investments in own embodied capital versus reproduction, and the quantity-quality and mating-parenting trade-offs can be understood in terms of investments in the embodied capital of offspring versus their number. The central thesis of this chapter is that there are four major factors affecting the timing of reproduction in the life course, reproductive rates, and parental investment for each sex: (1) the important resources consumed and utilized in reproduction and the production process by which those resources are obtained; (2) risks of mortality and the “technology” of mortality reduction; (3) the extent of complementarity between the sexes in the production of offspring; (4) the degree of variation in resource production and capital holdings among individuals and within individuals over time. With respect to the first factor, the relative impacts of mass-based, brain-based, and extrasomatic physical capital on resource production are critical determinants (see Figure 7-1). What are the marginal effects of an increase in body size on acquisition and turnover rates for energy and other critical resources? What are the marginal effects of increases in brain size, brain complexity, knowledge, and skill on resource production? How does physical capital, such as land or a breeding territory, affect production? How do body mass, brain-based abilities, and extrasomatic physical capital combine in resource production? The general expectation is that, since investments in each of those forms of capital trade off against each other and against allocations to reproduction, natural selection will optimize those investments so as to maximize descendent production. The brain is a special form of embodied capital. On the one hand, neural tissue monitors the organism’s internal and external environment and induces physiological and behavioral responses to stimuli (Jerison, 1973; 1976). On the other hand, the brain has the capacity to transform present experiences into future performance. This is particularly true of the cerebral cortex, which specializes in the storage, retrieval, and processing of experiences. To the extent that capital investments in the brain generate rewards that are realized over time (e.g., an increased reproductive rate during adulthood), the payoffs to those investments depend on mortality rates, since they affect the length of time over which the return will be realized. Dynamic models of this process show that investments in embodied capital coevolve with investments affecting mortality and longevity (Kaplan and Robson, 2002; Robson and Kaplan, 2003). The longer the time spent growing and learning prior to reproducing, the more natural

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Offspring: Human Fertility Behavior in Biodemographic Perspective FIGURE 7-1 Production as a function of the capital stock. NOTE: The relationship between production and each form of capital varies with ecology and the resources produced. Capital may be size-based, brain-based, or extrasomatic. More or less initial investment may be required before returns increase, and with further increases in investment, returns may diminish rapidly or slowly. selection favors investments in staying alive to reap the benefits of those investments. Similarly, any investments that produce increased energy capture rates later in life, such as learning, select for additional investments to reach those older ages. In addition to the production of energy, organisms can allocate energy and/or invest in forms of capital that reduce risks of mortality. While most biological models treat mortality as essentially exogenous, observed mortality is best understood in terms of an interaction between exogenous risks (environmental assaults) and endogenous responses designed to reduce mortality in the face of those risks. The technology of mortality reduction (the immune system, the ability to run, protective coverings such as shells, defensive weapons) also affects the likelihood of dying from environmental assaults. Models of embodied capital also show that ecological features or investments that increase the probability of survival to older ages also produce selection for greater investments in income-related embodied capi-

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Offspring: Human Fertility Behavior in Biodemographic Perspective FIGURE 7-2 Offspring viability isoclines (indifference curves) as a function of male and female inputs. tal. These coevolutionary effects appear to have been particularly important in human life history evolution. With respect to the third factor, complementarity, each parent in sexually reproducing species contributes approximately half the offspring’s genes and some amount of parental investment. The fitness of offspring is likely to be some function of the genetic material and the investments received from each parent. Each of these inputs may act as substitutes or complements, as illustrated in Figure 7-2. Stated simply, complementarity occurs when the value of male investment in offspring depends positively on the amount given by females and vice versa (with fitness held constant).2 In 2   Technically, complementarity occurs when marginal rates of substitution along fitness isoclines or indifference curves change as the ratio of the two inputs changes, making those curves convex to the origin.

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Offspring: Human Fertility Behavior in Biodemographic Perspective contrast, male and female inputs are substitutes when the relative values of the two inputs are independent of the amount provided by the other sex (again holding fitness constant). Thus, there are four axes of potential complementarity (e.g., between mother’s and father’s genes, between mother’s and father’s investment, and between each parent’s genes and their own and the other parent’s investments). Gains from specialization in parenting and/or mating effort and complementarity between genes and investment are forces favoring sexual dimorphism, with females typically specializing in parenting effort and males specializing in mating effort. Complementarity between the investments of each sex is the force favoring decreased sexual dimorphism and increased male parental investment. This kind of complementarity can occur when both direct care and resources are important to offspring viability and when the provisioning of each conflicts with, or is incompatible with, the provisioning of the other. For example, protection and feeding of nestlings are incompatible among many flying bird species. Protection of the young by one parent complements provisioning by the other parent, since food is only valuable to offspring that have not been preyed on. This ecology favors biparental investment and taking turns in feeding and nest protection by males and females. Among grazing mammals, however, offspring follow their mothers, who are able to nurse and protect them simultaneously. Investments by males in this case are less complementary and would only substitute for the investments of females. Mate choice criteria and mating “market” characteristics are expected to result from the variance among and within individuals over time with respect to the resources critical for reproduction. When females provide all the parental investment in response to the conditions discussed above, they are expected to exercise choice among males in terms of their genetic quality, and males are expected to compete with other males for access to fecund females, either through physical competition or appeals to female choice. As support from males increases in value with a resultant increase in their contribution to reproduction, we expect female choice to respond to variation in male offers of investment and in their ability to acquire resources utilized in reproduction. Males, in turn, as their investments in offspring increase, are expected to exert choice with respect to variation in female quality and to compete with other males for access to the resources utilized in reproduction. Ecological variability affecting the variance among males and females in resource access or access to mates is expected to exert a significant influence on mating market dynamics and in male and female investments in parenting and mating effort. Intertemporal variation in productivity within individuals is also likely to affect their mate value because it increases the likelihood of shortfalls.

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Offspring: Human Fertility Behavior in Biodemographic Perspective Our proposal is that human evolution has resulted in a specialized life history that is due to a particular constellation of the factors discussed above. This constellation derives from the hunter-gatherer way of life, which characterized the vast majority of human evolutionary history. While, as discussed in the next section, there are some universal features associated with this way of life, there is significant ecological variability across habitats. We also propose that as a result of exposure to such variation, human psychology and physiology have evolved to respond in systematic ways to variations in the four factors discussed above. Finally, the domestication of plants and animals and subsequent economic transformations produced new socioecological conditions to which people responded in radical shifts in parenting and mating practices. HUMAN LIFE HISTORIES IN A COMPARATIVE CONTEXT Relative to other mammalian orders, the primate order is slow growing, slow reproducing, long lived, and large brained. Humans are at the extreme of the primate continuum. Compared to other primates, there are at least four distinctive characteristics of human life histories: (1) an exceptionally long life span, (2) an extended period of juvenile dependence, resulting in families with multiple dependent children of different ages, (3) multigenerational resource flows and support of reproduction by older postreproductive individuals, and (4) male support of reproduction through the provisioning of females and their offspring. The brain and its attendant functional abilities are also extreme among humans. Our theory (Kaplan et al., 2000; Kaplan and Robson, 2002; Robson andd Kaplan, 2003) is that these extreme values with respect to brain size and longevity are coevolved responses to an equally extreme commitment to learning-intensive foraging strategies and a dietary shift toward high-quality, nutrient-dense, difficult-to-acquire food resources. The following logic underlies our proposal. First, high levels of knowledge, skill, coordination, and strength are required to exploit the suite of high-quality, difficult-to-acquire resources that humans consume. The attainment of those abilities requires time and a significant commitment to development. This extended learning phase during which productivity is low is compensated for by higher productivity during the adult period, with an intergenerational flow of food from old to young. Since productivity increases with age, the time investment in skill acquisition and knowledge leads to selection for lowered mortality rates and greater longevity because the returns on the investments in development occur at older ages. Second, the feeding niche specializing on large valuable food packages, and particularly hunting, promotes cooperation between men and women and high levels of male parental investment, because it favors sex-specific

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Offspring: Human Fertility Behavior in Biodemographic Perspective specialization in embodied capital investments and generates a complementarity between male and female inputs. The economic and reproductive cooperation between men and women facilitates provisioning of juveniles, which both bankrolls their embodied capital investments and acts to lower mortality during the juvenile and early adult periods. Cooperation between males and females also allows women to allocate more time to child care and improves nutritional status, increasing both survival and reproductive rates. The nutritional dependence of multiple young of different ages favors sequential mating with the same individual, since it reduces conflicts between men and women over the allocation of food. Finally, large packages also appear to promote interfamilial food sharing. Food sharing assists recovery in times of illness and reduces the risk of food shortfalls due to both the vagaries of foraging luck and the variance in family size due to stochastic mortality and fertility. These buffers against mortality also favor a longer juvenile period and higher investment in other mechanisms to increase life span. Thus, we propose that the long human life span, lengthening of the juvenile period, increased brain capacities for information processing and storage, intergenerational resource flows, and cooperative biparental investment in offspring coevolved in response to this dietary shift and the new production processes it entailed. It is not yet possible to know many vital statistics and behavioral characteristics from paleontological and archeological remains. It must be recognized that modern hunter-gatherers are not living replicas of our Stone Age past, and global socioeconomic forces affect them all. Furthermore, many foragers today live in marginalized habitats that underreward male hunting efforts. Yet despite the variable historical, ecological, and political conditions affecting them, there is remarkable similarity among foraging peoples, and even the variation often makes adaptive sense. Comparisons between foraging peoples and other modern primates are an important source of information about the life histories of our ancestors and the selection pressures acting on them, the subject of the next sections. Mortality and Production The age-specific mortality profile among chimpanzees is relatively V-shaped, decreasing rapidly after infancy to its lowest point (about 3 percent per year) at about age 13, the age of first reproduction for females, and increasing sharply thereafter. In contrast, mortality among human foragers decreases to a much lower point (about 0.5 percent per year) and remains low with no increase between about 15 and 40 years of age. Mortality then increases slowly, until there is a very rapid rise in the 60s and 70s. The pattern is much more block U-shaped. The strong similarities in the mortal-

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Offspring: Human Fertility Behavior in Biodemographic Perspective cially acquired, understanding cultural diffusion is critical. Evolutionary logic provides a framework for analysis of the active role that people play in determining which ideas they choose to adopt. ACKNOWLEDGMENTS This paper was written with support from the National Institute on Aging. The authors also wish to acknowledge the contributions of Kim Hill to the datasets and their analyses on the comparative diets and demography of chimpanzees and foragers published in a previous paper (Kaplan et al., 2000). We also thank Kim Hill and Magdalena Hurtado for their data on resource acquisition by age and sex among Hiwi and Ache. These datasets and analyses formed a critical base for part of this paper. We also wish to thank Monique Borgerhoff Mulder for her careful and extensive suggestions for revision of a draft of this paper. REFERENCES Anderson, K., H. Kaplan, D. Lam, and J. Lancaster 1999a Paternal care by genetic fathers and stepfathers II: Reports by Xhosa High School students. Evolution and Human Behavior 20:433-452. Anderson K.G., H. Kaplan, and D. Lam 2001 Grade repetition, schooling attainment and family background in South Africa. Unpublished manuscript. Population Studies Center, University of Michigan, Ann Arbor. Anderson, K.G., H. Kaplan, and J. Lancaster 1999b Paternal care by genetic fathers and stepfathers I: Reports from Albuquerque men. Evolution and Human Behavior 20:405-432. Bailey, R.C., M.R. Jenike, P.T. Ellison, G.R. Bentley, A.M. Harrigan, and N.R. Peacock 1992 The ecology of birth seasonality among agriculturalists in Central Africa. Journal of Biosocial Science 24:393-412. Becker, G.S. 1975 Human Capital. New York: Columbia University Press. Becker, G.S., and R.J. Barro 1988 A reformulation of the economic theory of fertility. Quarterly Journal of Economics 103:1-25. Bentley, G.R., R.R. Paine, and J.L. Boldsen 2001 Fertility changes with the prehistoric transition to agriculture. Pp. 203-232 in Reproductive Ecology and Human Evolution. P.T. Ellison, ed. Hawthorne, NY: Aldine de Gruyter. Betzig, L. 1986 Despotism and Differential Reproduction: A Darwinian View of History. Hawthorne, NY: Aldine de Gruyter. 1992a Roman monogamy. Ethology and Sociobiology 13:351-383. 1992b Roman polygyny. Ethology and Sociobiology 13:309-349.

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Offspring: Human Fertility Behavior in Biodemographic Perspective 1993 Sex, succession and stratification in the first six civilizations: How powerful men reproduced, passed power on to their sons, and used their power to defend their wealth, women and children. Pp. 37-74 in Social Stratification and Socioeconomic Inequality. L. Ellis, ed. New York: Praeger. Binford, L.R. 2001 Constructing Frames of Reference. Berkeley: University of California Press. Bird, D.W., and R. Bliege Bird 2002 Children on the reef: Slow learning or strategic foraging. Human Nature 13:269-297. Bliege Bird, R., and D.W. Bird 2002 Constraints of knowing or constraints of growing? Fishing and collecting among the children of Mer. Human Nature 13:00-00. Blake, J. 1989 Family Size and Achievement. Los Angeles: University of California Press. Blurton Jones, N.G., K. Hawkes, and J. O’Connell 1989 Modeling and measuring the costs of children in two foraging societies. Pp. 367-390 in Comparative Socioecology of Humans and Other Mammals. V. Standen and R.A. Foley, eds. London: Basil Blackwell. Blurton Jones, N.G., K. Hawkes, and P. Draper 1994a Differences between Hadza and !Kung children’s work: Original affluence or practical reason. Pp. 189-215 in Key Issues in Hunter-Gatherer Research. E.S. Burch, ed. Oxford: Berg. 1994b Foraging returns of !Kung adults and children: Why didn’t !Kung children forage? Journal of Anthropological Research 50:217-248. Bock, J. 1995 The Determinants of Variation in Children’s Activities in a Southern African Community. Ph.D. dissertation, University of New Mexico, Albuquerque. 1999 Evolutionary approaches to population: Implications for research and policy. Population and Environment 21:193-222. 2002 Learning, life history, and productivity: Children’s lives in the Okavango Delta, Botswana. Human Nature 13:161-198. Bongaarts, J., and R.G. Porter 1983 Fertility, Biology and Behavior: An Analysis of Proximate Determinants. New York: Academic Press. Boone, J. 1986 Parental investment and elite family structure in preindustrial states: A case study of late medieval-early modern Portuguese genealogies. American Anthropologist 88:259-278. 1988 Parental investment, social subordination and population processes among the 15th and 16th century Portuguese nobility. Pp. 201-220 in Human Reproductive Behavior: A Darwinian Perspective. L. Betzig, P. Turke, and M. Borgerhoff Mulder, eds. Cambridge: Cambridge University Press. Boone, J.L., and K.L. Kessler 1999 More status or more children? Social status, fertility reduction, and long-term fitness. Evolution and Human Behavior 20:257-277. Borgerhoff Mulder, M. 1988 Kipsigis bride wealth payments. In Human Reproductive Behavior. L. Betzig, M. Borgerhoff Mulder, and P. Turke, eds. Cambridge: Cambridge University Press. 1989 Early maturing Kipsigis women have higher reproductive success than late maturing women and cost more to marry. Behavioral Ecology and Sociobiology 24:145-153.

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Offspring: Human Fertility Behavior in Biodemographic Perspective 1991 Behavioural ecology of humans: Studies of foraging and reproduction. Pp. 69-98 in Behavioural Ecology. J.R. Krebs and N.B. Davies, eds. Oxford: Blackwell Scientific Publications. 1992 Demography of pastoralists: Preliminary data on the Datoga of Tanzania. Human Ecology 20:383-405. 1995 Bride wealth and its correlates: Quantifying changes over time. Current Anthropology 36:573-603. 1998 Brothers and sisters: How sibling interactions affect optimal parental investment. Human Nature 9:119-162. 2000 Optimizing offspring: The quantity-quality tradeoff in agropastoral Kipsigis. Evolution and Human Behavior 21:391-410. Boserup, E. 1970 Women’s Role in Economic Development. London: Allen and Unwin. Boswell, J. 1990 The Kindness of Strangers: The Abandonment of Children in Western Europe from Late Antiquity to the Renaissance. New York: Vintage Books. Brown, J.K. 1970 A note on the division of labor by sex. American Anthropologist 72:1073-1078. Burck, C.G. 1976 A group profile of the Fortune 500 child executives. Fortune (May Issue):173-177. Burman, S., and E. Preston-Whyte, eds. 1992 Questionable Issue: Illegitimacy in South Africa. Cape Town: Oxford University Press. Burman, S., and P. Reynolds, eds. 1986 Growing Up in a Divided Society: The Contexts of Childhood in South Africa. Johannesburg: Ravan Press. Burton, L. 1990 Teenage childbearing as an alternative life-course strategy in multigenerational black families. Human Nature 1:123-144. Chagnon, N.A. 1979 Is reproductive success equal in egalitarian societies? Pp. 374-401 in Evolutionary Biology and Human Social Behavior: An Anthropological Perspective. N.A. Chagnon and W. Irons, eds. North Scituate, MA: Duxbury Press. 1988 Life histories, blood revenge, and warfare in a tribal population. Science 239:985-992. 2000 Manipulating kinship rules: A form of male Yanomamo reproductive competition. Pp. 115-132 in Adaptation and Human Behavior: An Anthropological Perspective. L. Cronk, N. Chagnon, and W. Irons, eds. Hawthorne, NY: Aldine de Gruyter. Charnov, E.L. 1993 Life History Invariants: Some Explanations of Symmetry in Evolutionary Ecology. Oxford: Oxford University Press. Child Trends, Inc. 1995 Teen Births and Births to Unmarried Women: Facts at a Glance. Washington, DC: Author. 1996 New Data from Child Trends, Inc: Facts at a Glance. Washington, DC: Author. Clarke, A.L. and B.S. Low 1992 Ecological correlates of human dispersal in 19th century Sweden. Animal Behavior 44:677-693.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective 2001 Testing evolutionary hypotheses with demographic data. Population and Development Review 27:633-660. Clutton-Brock, T.H. 1991 The Evolution of Parental Care. Princeton, NJ: Princeton University Press. Clutton-Brock, T.H., and G.A. Parker 1992 Potential reproductive rates and the operation of sexual selection. Quarterly Review of Biology 67:437-456. Coale, A.J., and R. Treadway 1986 A summary of the changing distribution of overall fertility, marital fertility and the proportion married in the provinces of Europe. Pp. 31-181 in The Decline of Fertility in Europe. A.J. Coale and S.C. Watkins, eds. Princeton, NJ: Princeton University Press. Colson, E. 1960 Social Organization of the Gwembe Tonga. Manchester: Rhodes-Livingstone Institute. Cromer, A. 1993 Uncommon Sense: The Heretical Nature of Science. New York: Oxford University Press. Crook, J.H., and S.J. Crook 1988 Tibetan polyandry: Problems of adaptation and fitness. Pp. 97-114 in Human Reproductive Behavior: A Darwinian Perspective. L. Betzig, M. Borgerhoff Mulder, and P. Turke, eds. Cambridge: Cambridge University Press. Curtin, P.D. 1989 Death by Migration: Europe’s Encounter with the Tropical World in the Nineteenth Century. Cambridge: Cambridge University Press. Dickemann, M. 1979a The ecology of mating systems in hypergynous dowry societies. Social Science Information 18:163-195. 1979b Female infanticide and the reproductive consequences of stratified human societies. In Evolutionary Societies and Human Social Behavior. N.A. Chagnon, and W. Irons, eds. North Scituate, MA: Duxbury Press. 1981 Paternal confidence and dowry competition: A biocultural analysis of purdah. In Natural Selection and Social Behavior. R.D. Alexander and D.W. Tinkle, eds. New York: Chiron Press. DiVale, W., and M. Harris 1976 Population, warfare, and the male supremacist complex. American Anthropologist 80:21-41. Downey, D.B. 1995 When bigger is not better: Family size, parental resources, and children’s education performance. American Sociological Review 60:746-761. Draper, P. 1992 Room to maneuver: !Kung women cope with men. Pp. 43-63 in Sanctions and Sanctuary: Cultural Perspectives on the Beating of Wives. D. Counts, J.K. Brown, and J. Campbell, eds. Boulder, CO: Westview Press. Dunbar, R.I.M. 1991 Sociobiological theory and the Cheyenne case. Current Anthropology 32:169-173. Ellison, P.T. 2001a On Fertile Ground: A Natural History of Human Reproduction. Cambridge, MA: Harvard University Press.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective Ellison, P.T., ed. 2001b Reproductive Ecology and Human Evolution. Hawthorne, NY: Aldine de Gruyter. Ember, C.R. 1983 The relative decline in women’s contributions to agriculture with intensification. American Anthropologist 85:285-304. Gaulin, S., and J. Boster 1990 Dowry as female competition. American Antrhopologist 92:994-1005. Geronimus, A.T. 1996 What teen mothers know. Human Nature 7:323-352. Geronimus, A.T., J. Bound, and T.A. Waidmann 1999 Health inequality and population variation in fertility timing. Social Science and Medicine 49:1623-1636. Geronimus, A.T., and S. Korenman 1992 The socioeconomic consequences of teen childbearing reconsidered. The Quarterly Review of Economics 107:1187-1214. Godfray, H.C.J., L. Partridge, and P.H. Harvey 1991 Clutch size. Annual Review of Ecology and Systematics 22:409-429. Goodale, J.C. 1971 Tiwi Wives. Seattle: University of Washington Press. Goody, J. 1973 Bride wealth and dowry in Africa and Eurasia. In Bride Wealth and Dowry. J.R. Goody and S.J. Tambiah, eds. Cambridge: Cambridge University Press. 1976 Production and Reproduction: A Comparative Study of the Domestic Domain. Cambridge: Cambridge University Press. 1983 The Development of the Family and Marriage in Europe. Cambridge: Cambridge University Press. Grafen, A. 1991 Modeling a behavioural ecology. Pp. 5-31 in Behavioural Ecology: An Evolutionary Approach. J.R. Krebs and N.B. Davies, eds. Oxford: Blackwell Scientific. Gurven, M., K. Hill, H. Kaplan, M. Hurtado, and R. Lyles 2000 Food transfers among Hiwi foragers of Venezuela: Tests of reciprocity. Human Ecology 28:171-218. Gwyne, D.T. 1991 Sexual competition among females: What causes courtship role reversal. Trends in Evolution and Ecology 6:118-1222. Gwyne, D.T., and L.W. Simmons 1990 Experimental reversal of courtship roles in an insect. Nature 346:172-174. Haaga, J.G. 2001 Comment: The pace of fertility decline and the utility of evolutionary approaches. In Global Fertility Transition, R.A. Bulatao, and J.B. casterline, eds. Population and Development Review (suppl) 27:53-59. Haddix, K. 2001 When polyandry falls apart: Leaving your wife and your brothers. Evolution and Human Behavior 22:47-60. Harpending, H. 1994 Infertility and hunter-gatherer demography. American Journal of Physical Anthropology 93:385-390. Hart, B., and T. Risley 1995 Meaningful Differences in the Everyday Experience of Young American Children. Baltimore, MD: Brookes.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective Hart, C.W.M., and A.R. Pilling 1960 The Tiwi of North Australia. New York: Holt, Rinehart and Winston. Hartung, J. 1982 Polygyny and the inheritance of wealth. Current Anthropology 23:1-12. Hawkes, K., and R.Bliege Bird 2002 Showing off, handicap signaling, and the evolution of men’s work. Evolutionary Anthropology 11:58-67. Hawkes, K., J.F. O’Connell, and H.G. Blurton Jones 1995 Hadza children’s foraging: Juvenile dependency, social arrangements and mobility among hunter-gatherers. Current Anthropology 36:688-700. Herrnstein, R.J., and C. Murray 1994 The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press. Hill, K., and A.M. Hurtado 1991 The evolution of reproductive senescence and menopause in human females. Human Nature 2:315-350. 1996 Ache Life History: The Ecology and Demography of a Foraging People. Hawthorne, NY: Aldine. Hoff-Ginsberg, E., and T. Tardiff 1995 Socioeconomic status and parenting. In The Handbook of Parenting. M. Bornstein, ed. Hillsdate, NJ: Erlbaum. Hrdy, S.B. 1994 Fitness tradeoffs in the history and evolution of delegated mothering with special reference to wet-nursing, abandonment, and infanticide. In Infanticide and Parental Care. S. Parmigiani and F.S. vom Saal, eds. Chur, Switzerland: Harwood Academic Publishers. 1999 Mother Nature: A History of Mothers, Infants, and Natural Selection. New York: Pantheon. Hrdy, S.B., and D. Judge 1993 Darwin and the puzzle of primogeniture: An essay on biases in parental investment after death. Human Nature 4:1-45. Hughes, A.L. 1986 Reproductive success and occupational class in eighteenth-century Lancashire, England. Social Biology 33:109-115. Hurtado, A.M., K. Hawkes, K. Hill, and H. Kaplan 1985 Female subsistence strategies among Ache hunter-gatherers of Eastern Paraguay. Human Ecology 13:29-47. Hurtado, A.M., and K. Hill 1990 Seasonality in a foraging society: Variation in diet, work effort, fertility, and the sexual division of labor among the Hiwi of Venezuela. Journal of Anthropological Research 46:293-345. Irons, W. 1979a Cultural and biological success. Pp. 257-272 in Natural Selection and Social Behavior. N.A. Chagnon and W. Irons, eds. North Scituate, MA: Duxbury Press. 1979b Investment and primary social dyads. Pp. 181-213 in Evolutionary Biology and Human Social Behavior. N.A. Chagnon and W. Irons, eds. North Scituate, MA: Duxbury Press. Isbell, L.A. 1991 Contest and scramble competition: Patterns of female aggression and ranging behavior among primates. Behavioral Ecology 2:143-155.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective Jasienska, G. 2000 Why energy expenditure causes reproductive suppression in women. Pp. 59-84 in Reproductive Ecology and Human Evolution. P. Ellison, ed. Hawthorne, NY: Aldine de Gruyter. Jerison, H. 1973 Evolution of the Brain and Intelligence. New York: Academic Press. 1976 Paleoneurology and the evolution of mind. Scientific American 234:90-101. Kaplan, H.S. 1996 A theory of fertility and parental investment in traditional and modern human societies. Yearbook of Physical Anthropology 39:91-135. Kaplan, H.S., and K. Hill 1985 Hunting ability and reproductive success among male Ache foragers. Current Anthropology 26:131-133. Kaplan, H.S., and J.B. Lancaster 2000 The evolutionary economics and psychology of the demographic transition to low fertility. Pp. 238-322 in Human Behavior and Adaptation: An Anthropological Perspective. L. Cronk, W. Irons, and N. Chagnon, eds. Hawthorne, NY: Aldine de Gruyter. Kaplan, H., K. Hill, A.M. Hurtado, J. Lancaster, and R. Robson 2001a Embodied Capital and the Evolutionary Economics of the Human Lifespan. Albuquerque: University of New Mexico. Kaplan, H.S., K. Hill, A.M. Hurtado, and J.B. Lancaster 2001b The embodied capital theory of human evolution. Pp. 293-318 in Reproductive Ecology and Human Evolution. P.T. Ellison, ed. Hawthorne, NY: Aldine de Gruyter. Kaplan, H., K. Hill, J.B. Lancaster, and A.M. Hurtado 2000 A theory of human life history evolution: Diet, intelligence, and longevity. Evolutionary Anthropology 9:156-185. Kaplan, H.S., J. Lancaster, J. Bock, and S. Johnson 1995 Does observed fertility maximize fitness among New Mexican men? A test of an optimality model and a new theory of parental investment in the embodied capital of offspring. Human Nature 6:325-360. Kaplan, H.S., J.B. Lancaster, W.T. Tucker, and K.G. Anderson 2002 An evolutionary approach to below replacement fertility. American Journal of Human Biology 14:1-24. Kaplan, H.S., and A. Robson 2002 The emergence of humans: the coevolution of intelligence and longevity with intergenerational transfers. Proceedings of the National Academy of Sciences 99(15):10221-10226. Keeley, L.H. 1996 War Before Civilization: The Myth of the Peaceful Savage. Oxford: Oxford University Press. Kirwin, M. 1979 African Widows. Maryknoll: Orbis. Kozlowski, J., and R.G. Weigert 1987 Optimal age and size at maturity in the annuals and perennials with determinant growth. Evolutionary Ecology 1:231-244. Kramer, K. 2002 Variability in the duration of juvenile dependence: The benefits of Maya children’s work to parents. Human Nature 13:299-325.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective Kuzawa, C.W. 1998 Adipose tissue in human infancy and childhood: An evolutionary perspective. Yearbook of Physical Anthropology 41:177-209. Lack, D. 1968 Ecological Adaptations for Breeding in Birds. London: Methuen. Lancaster, C.S. 1981 The Goba of the Zambezi: Sex Roles, Economics, and Change. Norman, OK: University of Oklahoma Press. Lancaster, J.B. 1989 Evolutionary and cross-cultural perspectives on single parenthood. Pp. 63-72 in Sociobiology and the Social Sciences. R.W. Bell and N.J. Bell, eds. Lubbock: Texas Tech University Press. 1997 The evolutionary history of human parental investment in relation to population growth and social stratification. Pp. 466-489 in Feminism and Evolutionary Biology. P.A. Gowaty, ed. New York: Chapman and Hall. Lancaster, J.B., and H. Kaplan 1992 Human mating and family formation strategies: The effects of variability among males in quality and the allocation of mating effort and parental investment. In Topics in Primatology: Human Origins. T. Nishida, W.C. McGrew, P. Marler, M. Pickford, and F. de Waal, eds. Tokyo: University of Tokyo Press. Lancaster, J.B., H. Kaplan, K. Hill, and A.M. Hurtado 2000 The evolution of life history, intelligence and diet among chimpanzees and human foragers. Pp. 47-72 in Perspectives in Ethology: Evolution, Culture and Behavior. F. Tonneau and N.S. Thompson, eds. New York: Plenum. Lawrence, M., and R.G. Whitehead 1988 Physical activity and total energy expenditure of child-bearing Gambian village women. European Journal of Clinical Nutrition 42:145-160. Low, B.S. 1990 Occupational status, landownership, and reproductive behavior in 19th-century Sweden: Tuna parish. American Anthropologist 92:457-468. 1991 Reproductive life in nineteenth century Sweden: An evolutionary perspective on demographic phenomena. Ethology and Sociobiology 12:411-448. 1994 Men in the demographic transition. Human Nature 5:223-253. 2000 Why Sex Matters: A Darwinian Look at Human Behavior. Princeton, NJ: Princeton University Press. Lummaa, V., and T. Clutton-Brock 2002 Early development, survival and reproduction in humans. Trends in Ecology and Evolution 17:141-147. Luttbeg, B., M. Borgerhoff Mulder, and M.S. Mangel 2000 To marry again or not: A dynamic model for demographic transition. Pp. 345-368 in Adaptation and Human Behavior: An Anthropological Perspective. L. Cronk, N.A. Chagnon, and W. Irons, eds. Hawthorne, NY: Aldine de Gruyter. Lutz, W., W. Sanderson, and S. Scherbov 2001 The end of world population growth. Nature 412:543-545. Mace, R. 2000 An adaptive model of human reproductive rate where wealth is inherited: Why people have small families. Pp. 261-282 in Adaptation and Human Behavior: An Anthropological Perspective. L. Cronk, N.A. Chagnon, and W. Irons, eds. Hawthorne, NY: Aldine de Gruyter. Manson, J., and R. Wrangham 1991 Intergroup aggression in chimpanzees and humans. Current Anthropology 32:369-390.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective McDade, T.W. 2001 Parent-offspring conflict and the cultural ecology of breast feeding. Human Nature 12:9-25. Mueller, U. 2001 Is there a stabilizing selection around average fertility in modern human populations? Population and Development Review 27:469-498. Murdock, G.P. 1967 Ethnographic atlas: A summary. Ethnology 6:109-236. Newcomer, M. 1955 The Big Business Executive: The Factors that Made Him, 1890-1950. New York: Columbia University Press. Orians, G.H. 1969 On the evolution of mating systems in birds and mammals. American Naturalist 103:589-603. Partridge, L., and P. Harvey 1985 Costs of reproduction. Nature 316:20-21. Pennington, R. 2001 Hunter-gatherer demography. Pp. 170-204 in Hunter-Gatherers: An Interdisciplinary Perspective. C. Panter-Brick, R.H. Layton, and P. Rowley-Conwy, eds. Cambridge: Cambridge University Press. Pike, I.L. 1999 Age, reproductive history, seasonality, and maternal body composition during pregnancy for nomadic Turkana of Kenya. American Journal of Human Biology 11:658-672. Poppitt, S.D., A.M. Prentice, E. Jequier, Y. Schutz, and R.G. Whitehead 1993 Evidence of energy sparing in Gambian women during pregnancy: A longitudinal study using whole-body calorimetry. American Journal of Clinical Nutrition 57:353-364. Potts, M. 1997 Sex and the birth rate. Population and Development Review 23:1-19. Prentice, A.M., and R.G. Whitehead 1987 The energetics of human reproduction. Symposium of the Zoological Society of London 57:275-304. Preston, S., and M. Haines 1991 Fatal Years: Child Mortality in Late Nineteenth Century America. Princeton, NJ: Princeton University Press. Promislow, D.E.L., and P.H. Harvey 1990 Living fast and dying young: A comparative analysis of life history variation among mammals. Journal of Zoology 220:417-437. Retherford, R.D. 1993 Demographic Transition and the Evolution of Intelligence: Theory and Evidence. Honolulu: East-West Center. Robson, A., and H.S. Kaplan 2003 The coevolution of intelligence and life expectancy in hunter-gatherer economies. American Economics Review (in press). Rogers, A. 1993 Why menopause? Evolutionary Ecology 7:406-420. Scott, S., and C.J. Duncan 1999 Reproductive strategies and sex-biased investment. Human Nature 10:85-108.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective Sear, R., R. Mace, and I.A. McGregor 2001 Determinants of fertility in rural Gambia: An evolutionary ecological approach. Paper presented at the General Population Conference, International Union for the Scientific Study of Population. Sellen, D.W., and R. Mace 1997 Fertility and mode of subsistence: A phylogenetic analysis. Current Anthropology 38:878-889. Sellen, D.W., and D.B. Smay 2001 Relationship between subsistence and age at weaning in “pre-industrial” societies. Human Nature 12:47-87. Shanley, D.P., and T.B.L. Kirkwood 2000 Calorie restriction and aging: A life-history analysis. Evolution 54:740-750. Smith, C.C., and S.D. Fretwell 1974 The optimal balance between size and number of offspring. American Naturalist 108:499-506. Stack, C. 1974 All Our Kin: Strategies for Survival in a Black Community. New York: Harper & Row. Sterck, E.H.M., D.P. Watts, and C.P. van Schaik 1997 The evolution of female social relationships in nonhuman primates. Behavioral Ecology and Sociobiology 41:291-309. Svedberg, P. 1990 Undernutrition in Sub-Saharan Africa: Is there a gender bias? Journal for Development Studies 26:469-486. Szreter, S., and E. Garrett 2000 Reproduction, compositional demography, and economic growth in early modern England. Population and Development Review 26:45-80. Tatar, M., D.W. Grey, and J.R. Carey 1997 Altitudinal variation in senescence in a Melanoplus grasshopper species complex. Oecologia 111:357-364. Towner, M. 1999 A dynamic model of human dispersal in a land-based economy. Behavioral Ecology and Sociobiology 46:82-94. 2001 Linking dispersal and resources in humans: Life history data from Oakham, Massachusetts (1750-1850). Human Nature 12:321-350. Trivers, R.L. 1972 Parental investment and sexual selection. In Sexual Selection and the Descent of Man, 1871-1971. B. Campbell, ed. Chicago: Aldine. Tucker, M.B., and C. Mitchell-Kernan 1995 The Decline in Marriage Among African Americans: Causes, Consequences, and Policy Implications. New York: Russell Sage Foundation. Vining, D.R. 1986 Social versus reproductive success: The central theoretical problem of human sociobiology. Behavioral and Brain Sciences 9:167-216. Vinovskis, M.A. 1994 Education and the economic transformation of nineteenth century America. Pp. 171-196 in Age and Structural Lag: Society’s Failure to Provide Meaningful Opportunities in Work, Family, and Leisure. M.W. Riley, R.L. Kahn, and A. Foner, eds. New York: John Wiley & Sons. Voland, E. 1990 Differential reproductive success with the Krummhorn population (Germany, 18th and 19th centuries) . Behavioral Ecology and Sociobiology 26:65-72.

OCR for page 170
Offspring: Human Fertility Behavior in Biodemographic Perspective 2000 Contributions of family reconstitution studies to evolutionary reproductive ecology. Evolutionary Anthropology 9:134-146. Voland, E., and A. Chasiotis 1998 How female reproductive decisions cause social inequality in male reproductive fitness: Evidence from eighteenth- and nineteenth-century Germany. Pp. 220-238 in Human Biology and Social Inequality. S.S. Strickland and P.S. Shetty, eds. Cambridge: Cambridge University Press. Voland, E., and R.I.M. Dunbar 1995 Resource competition and reproduction: The relationship between economic and parental strategies in the Krummhorn Population (1720-1874). Human Nature 6:33-49. 1997 The impact of social status and migration of female age at marriage in an historical population in north-west Germany. Journal of Biosocial Science 29:355-360. Voland, E., R.I.M. Dunbar, C. Engel, and P. Stephan 1997 Population increase and sex-biased parental investment: Evidence from 18th and 19th Century Germany. Current Anthropology 38:129-135. Voland, E., and C. Engel 1990 Female choice in humans: A conditional mate selection strategy of the Krummhorn women (Germany, 1720-1874). Ethology 84:144-154. Voland, E., E. Suegrekjiwm, and C. Engel 1991 Cost/benefit oriented parental investment by high status families: The Krummhorn case. Ethology and Evolutionary Biology 12:105-118. Weiss, Y., and R.J. Willis 1985 Children as collective goods and divorce settlements. Journal of Labor Economics 3:268-292. Werner, E.E. 1986 Amphibian metamorphosis: Growth rate, predation risk and the optimal time to transform. American Naturalist 128:319-341. White, D.R., and M.L. Burton 1988 Causes of polygyny: Ecology, economy, kinship, and warfare. American Anthropologist 90:871-887. Williams, G.C. 1957 Pleitropy, natural selection and the evolution of senescence. Evolution 11:398-411. Willis, R.J. 1987 Public and private intergenerational transfers, economic growth and demographic transition. Pp. 717-740 in Conference on Economic Development and Social Welfare in Taiwan. Taipei, Taiwan: Institute of Economics, Academica Sinica. 1994 Economic analysis of fertility: Micro foundations and aggregate implications. Pp. 139-171 in Population, Economic Development, and the Environment. K.L. Kiessling and H. Landberg, eds. New York: Oxford University Press. Willis, R.J., and J.G. Haaga 1996 Economic approaches to understanding nonmarital fertility. In Fertility in the United States: New Patterns, New Theories. J.D. Casterline, R.D. Lee, and K.A. Foote, eds. New York: The Population Council. Wood, J.W. 1994 Dynamics of Human Reproduction: Biology, Biometry and Demography. New York: Aldine de Gruyter.