An analysis of the sexual reproduction practices of the ache people

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An analysis of the sexual reproduction practices of the ache people

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Kaplan and Jane B. 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.

THE THEORETICAL FRAMEWORK

Sexual dimorphism and its relationship to mating systems together are the third theme. Each of these themes is addressed from two perspectives: 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.

Offspring: Human Fertility Behavior in Biodemographic Perspective.

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 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. 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.

In fact, all other fitness components, such as mortality, only affect fitness through their effects on fertility e. 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 includedsome 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. 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, 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.

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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.

An analysis of the sexual reproduction practices of the ache people

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,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: Sexual reproduction involves two components: 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 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 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, 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.An account is given of Christianity as a religion, describing its origin, an analysis of the sexual reproduction practices of the ache people its relation to other religions, automobiles the single greatest source of pollution its essential nature and chief characteristics, but not Search.

Recent Posts. Start studying Anthro Test 1. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Search. True. Anthropologist John Hawk's research on the relationship between the genes of living and ancient people show that. how does one refrain from judging such cultural practices as infanticide, geronticide, or wife.

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An analysis of the sexual reproduction practices of the ache people