Sociality, Hierarchy, Health Comparative Biodemography: A Collection of Papers (2014) / Chapter Skim
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8 Social and Economic Underpinnings of Human Biodemography--Paul L. Hooper, Michael Gurven, and Hillard Kaplan
8 Social and Economic Underpinnings of Human Biodemography--Paul L. Hooper, Michael Gurven, and Hillard Kaplan
Pages 169-196
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From page 169... ...
Our proposal is that three distinctive forms of social relationships evolved and were likely to have been present in most populations prior to the advent of agriculture: (1) kin-based altruism, with net downward transfers of food energy and other forms of assistance across generations; (2)
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From page 170... ...
Given that we cannot directly observe the social relationships, demographic characteristics, and behavioral patterns of prehistoric populations during human evolution, we are reliant on data derived from the paleoarcheological record, primatology, and the study of contemporary human populations. The quantitative study of extant human groups engaged in foraging or a mix of foraging and rudimentary horticulture (forager- horticulturalists)
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From page 171... ...
In the following sections, we provide a characterization of modal patterns of social organization and demography among human foragers. For each of the key social relationships introduced above -- kin-based altruism within families, cooperative pair-bonds, and reciprocal cooperation -- we discuss insights derived from evolutionary economic models, and review available evidence from the study of modern human foragers and other small-scale human societies.
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From page 172... ...
Data on diet from chimpanzees in the Gombe reserve in Tanzania indicate that about 95 percent of calories are derived from leaves and fruit. In contrast, for the sample of 10 human foraging societies for which quantitative data are available, fruits constitute an average of only 10 percent of the diet.
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From page 173... ...
post-reproductive sur vival. Analytical models of life history evolution show that exogenous shifts 1 Because most of these data are cross-sectional, secular trends may confuse age trends.
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From page 174... ...
These effects are expected to interact positively with the degree of relatedness. This logic provides a basis for understanding variation in parental investment, and net transfers of energy, time, and effort between kin more generally.
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From page 175... ...
and net food transfers (right panel) within Tsimane extended families.
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From page 176... ...
, theory in evolutionary biology emphasizes fitness impacts of choice for male genetic quality versus paternal investment. For males, it focuses on fitness impacts of paternal investment versus investments in mating effort -- for example, in displays of genetic quality or contests with other males.
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From page 177... ...
Figure 8-4 depicts two different kinds of ecological conditions affecting the gains from biparental investment. Figure 8-4a represents what we hypothesize to be the modal mammalian pattern, with a convex budget constraint for individual parents (the solid black line)
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From page 178... ...
Conditions favoring biparental investment As individual As individual As pair As pair C Care → Care → D A B Energy → Energy → FIGURE 8-4 Hypothetical budget constraints reflecting tradeoffs between the pro vision of care and energy by parents to offspring. NOTE: The solid black lines represent the feasible levels of care and energy which a single parent can provide, while the dashed black lines represent the levels of care and energy that two parents can provide together.
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From page 179... ...
These conditions reflect a relatively harsher tradeoff between providing care versus energy and support biparental investment. This would occur, for example, where young are unable to accompany adults while foraging, but face high risks of predation if left unattended; where foraging activites would expose offspring to high levels of risk; or where foraging returns rates would greatly suffer if offspring accompanied adults.
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From page 180... ...
. There is substantial variability across foraging societies in male and female energy inputs, but there are no societies reported for which men are not important providers of meat (with the possible exception of some aboriginal Australian groups for which quantitative data do not exist)
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From page 181... ...
As male parental investment is rare among mammals, male-male competition tends to be high, leading to both later onset of reproduction and earlier termination of reproduction among males, compared with females (because it takes males longer to become competitive than for females to begin reproducing, and the effects of senescencing competitive abilities affects male reproduction more than female; Clutton-Brock, 1991; Clutton-Brock and Isvaran, 2007; see also Alberts et al., this volume)
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From page 182... ...
Two different theories have been advanced to explain the extent of food sharing in hunting and gathering societies, both of which emphasize the importance of variability in food supply. According to one view, r eciprocity-based risk reduction drives food transfers; according to the other, food transfers are the result of tolerated theft.
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From page 183... ...
By smoothing variability in intake rates, foragers maximized the nutritional benefit from large food packages. The "tolerated theft" ypothesis proposes h that large food packages create variation among individuals in their available food, with the "lucky" individuals possessing larger and the unlucky ones smaller quantities or none (Blurton Jones, 1984)
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From page 184... ...
The vertical axis indicates the mean percent of food items shared with each family. Large foods with more vari able return rates are shared with a broader network of social partners than smaller, less variable foods.
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From page 186... ...
If, at equilibrium, an average man can only support all the children of one woman, the gains from dominance over other men may be small. The gains from risk reduction, cooperative acquisition, and male parental investment may thus combine to generate the relatively egalitarian patterns of interaction that seem to characterize so many foraging groups and that differ markedly from most other primate species.
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From page 187... ...
One reason would be decreased gains from male parental investment, motivating women to choose males more on the basis of genetic quality, and motivating men to invest more in mating competition. The second reason is that, under conditions of high interpersonal violence, male protection may become a more critical input into wife and offspring success.
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From page 188... ...
. Seasonal variation in resource availability and patchiness can also have dramatic effects on this aspect of social organization.
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From page 189... ...
the coupling of male and female reproductive careers, biparental investment, and cooperative pair-bonds; and (3) survival and cooperative social insurance.
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From page 190... ...
The second avenue of insight into modern human behavior may stem from the theoretical principles that appear to order the data collected among foraging societies. The gains from investments in skill and other factors affecting age profiles of productivity, such as health in old age, may help explain patterns of inter enerational transfers and parental investment that change g over time and depend on socioeconomic status.
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From page 191... ...
. To give and to give not: The behavioral ecology of human food transfers.
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From page 192... ...
. From the womb to the tomb: The role of transfers in shaping the evolved human life history.
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From page 193... ...
. A theory of human life history evolution: Diet, intelligence, and longevity.
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From page 194... ...
. Parental investment, sexual selection and sex ratios.
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From page 195... ...
. Why men matter: Mating pat terns drive evolution of human lifespan.
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