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Ross CT, Mulder MB, Oh SY, Bowles S, Beheim B, Bunce J, Caudell M, Clark G, Colleran H, Cortez C, Draper P, Greaves RD, Gurven M, Headland T, Headland J, Hill K, Hewlett B, Kaplan HS, Koster J, Kramer K, Marlowe F, McElreath R, Nolin D, Quinlan M, Quinlan R, Revilla-Minaya C, Scelza B, Schacht R, Shenk M, Uehara R, Voland E, Willführ K, Winterhalder B, Ziker J. Correction to: ‘Greater wealth inequality, less polygyny: rethinking the polygyny threshold model’. J R Soc Interface 2018; 15:rsif.2018.0752. [PMID: 30381348 PMCID: PMC6228491 DOI: 10.1098/rsif.2018.0752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
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Ross CT, Borgerhoff Mulder M, Oh SY, Bowles S, Beheim B, Bunce J, Caudell M, Clark G, Colleran H, Cortez C, Draper P, Greaves RD, Gurven M, Headland T, Headland J, Hill K, Hewlett B, Kaplan HS, Koster J, Kramer K, Marlowe F, McElreath R, Nolin D, Quinlan M, Quinlan R, Revilla-Minaya C, Scelza B, Schacht R, Shenk M, Uehara R, Voland E, Willführ K, Winterhalder B, Ziker J. Greater wealth inequality, less polygyny: rethinking the polygyny threshold model. J R Soc Interface 2018; 15:20180035. [PMID: 30021924 PMCID: PMC6073648 DOI: 10.1098/rsif.2018.0035] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2018] [Accepted: 06/25/2018] [Indexed: 11/12/2022] Open
Abstract
Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.
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Affiliation(s)
- Cody T Ross
- Behavioral Sciences Program, Santa Fe Institute, Santa Fe, NM, USA
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | | | - Seung-Yun Oh
- Korea Insurance Research Institute, Yeongdeungpo-gu, Republic of Korea
| | - Samuel Bowles
- Behavioral Sciences Program, Santa Fe Institute, Santa Fe, NM, USA
| | - Bret Beheim
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - John Bunce
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - Mark Caudell
- Allen School for Global Animal Health, Washington State University, Pullman, WA, USA
| | - Gregory Clark
- Department of Anthropology, University of California, Davis, CA, USA
| | - Heidi Colleran
- Dept. of Linguistic and Cultural Evolution, Max Planck Institute for the Science of Human History, Leipzig, Germany
| | - Carmen Cortez
- Department of Anthropology, University of California, Davis, CA, USA
| | - Patricia Draper
- Department of Anthropology, University of Nebraska, Lincoln, NE, USA
| | | | - Michael Gurven
- Department of Anthropology, University of California, Santa Barbara, CA, USA
| | | | | | - Kim Hill
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA
| | - Barry Hewlett
- Department of Anthropology, Washington State University, Vancouver, WA, USA
| | - Hillard S Kaplan
- Department of Anthropology, University of New Mexico, Albuquerque, NM, USA
| | - Jeremy Koster
- Department of Anthropology, University of Cincinnati, Cincinnati, OH, USA
| | - Karen Kramer
- Department of Anthropology, University of Utah, Logan, UT, USA
| | - Frank Marlowe
- Department of Biological Anthropology, University of Cambridge, UK
| | - Richard McElreath
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - David Nolin
- Department of Anthropology, Pennsylvania State University, Philadelphia, PA, USA
| | - Marsha Quinlan
- Department of Anthropology, Washington State University, Vancouver, WA, USA
| | - Robert Quinlan
- Department of Anthropology, Washington State University, Vancouver, WA, USA
| | | | - Brooke Scelza
- Department of Anthropology, University of California, Los Angeles, CA, USA
| | - Ryan Schacht
- Department of Anthropology, University of Utah, Logan, UT, USA
| | - Mary Shenk
- Department of Anthropology, Pennsylvania State University, Philadelphia, PA, USA
| | | | - Eckart Voland
- Institut für Philosophie der Universität Giessen, Giessen, Germany
| | - Kai Willführ
- Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | | | - John Ziker
- Department of Anthropology, Boise State University, Boise, ID, USA
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Cashdan E, Kramer KL, Davis HE, Padilla L, Greaves RD. Mobility and Navigation among the Yucatec Maya: Sex Differences Reflect Parental Investment, Not Mating Competition. Hum Nat 2017; 27:35-50. [PMID: 26650606 PMCID: PMC4742514 DOI: 10.1007/s12110-015-9250-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Sex differences in range size and navigation are widely reported, with males traveling farther than females, being less spatially anxious, and in many studies navigating more effectively. One explanation holds that these differences are the result of sexual selection, with larger ranges conferring mating benefits on males, while another explanation focuses on greater parenting costs that large ranges impose on reproductive-aged females. We evaluated these arguments with data from a community of highly monogamous Maya farmers. Maya men and women do not differ in distance traveled over the region during the mate-seeking years, suggesting that mating competition does not affect range size in this monogamous population. However, men’s regional and daily travel increases after marriage, apparently in pursuit of resources that benefit families, whereas women reduce their daily travel after marriage. This suggests that parental effort is more important than mating effort in this population. Despite the relatively modest overall sex difference in mobility, Maya men were less spatially anxious than women, thought themselves to be better navigators, and pointed more accurately to distant locations. A structural equation model showed that the sex by marital status interaction had a direct effect on mobility, with a weaker indirect effect of sex on mobility mediated by navigational ability.
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Affiliation(s)
- Elizabeth Cashdan
- Department of Anthropology, University of Utah, Salt Lake City, UT, USA
| | - Karen L Kramer
- Department of Anthropology, University of Utah, Salt Lake City, UT, USA.
| | - Helen E Davis
- Department of Anthropology, University of Utah, Salt Lake City, UT, USA
| | - Lace Padilla
- Department of Psychology, University of Utah, Salt Lake City, UT, USA
| | - Russell D Greaves
- Peabody Museum of Archaeology and Ethnology, Harvard University, Cambridge, MA, USA
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Veile A, Winking J, Gurven M, Greaves RD, Kramer KL. Infant growth and the thymus: data from two South American native societies. Am J Hum Biol 2012; 24:768-75. [PMID: 22915311 DOI: 10.1002/ajhb.22314] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 03/31/2012] [Accepted: 07/16/2012] [Indexed: 11/11/2022] Open
Abstract
The thymus plays an important role in the development of the immune system, yet little is known about the patterns and sources of variation in postnatal thymic development. The aim of this study is to contribute cross-cultural data on thymus size in infants from two South American native populations, the Tsimane of Bolivia and the Pumé of Venezuela. Thymic ultrasonography was performed and standard anthropometric measures collected from 86 Tsimane and Pumé infants. Patterns of infant growth and thymus size were compared between the two populations and the relationship between nutritional status and thymus size was assessed. Despite nearly identical anthropometric trajectories, Tsimane infants had larger thymuses than Pumé infants at all ages. Population, infant age, and infant mid-upper arm circumference were significant predictors of thymus area in the Tsimane and Pumé infants. This finding reveals a cross-cultural difference in thymus size that is not driven by nutritional status. We suggest that future studies focus on isolating prenatal and postnatal environmental factors underlying cross-cultural variation in thymic development.
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Affiliation(s)
- Amanda Veile
- Department of Human Evolutionary Biology, Harvard University, Cambridge Massachusetts 02138, USA.
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Kramer KL, Greaves RD. Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragers. Am J Phys Anthropol 2010; 141:235-44. [PMID: 19844999 DOI: 10.1002/ajpa.21139] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food-limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments.
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Affiliation(s)
- Karen L Kramer
- Department of Anthropology, Harvard University, Cambridge, MA 02138, USA.
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Kramer KL, Greaves RD, Ellison PT. Early reproductive maturity among Pumé foragers: Implications of a pooled energy model to fast life histories. Am J Hum Biol 2009; 21:430-7. [PMID: 19402033 DOI: 10.1002/ajhb.20930] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
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.
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Affiliation(s)
- Karen L Kramer
- Department of Anthropology, Harvard University, Cambridge, Massachusetts 02138, USA.
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