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Belinchón M, Polo P, Rodriguez-Sickert C, Figueroa O, Valenzuela N, Pavez P, Muñoz-Reyes JA. The effect of intergroup competition outcome on ingroup cooperation: insights from the male warrior hypothesis. Front Psychol 2024; 15:1303372. [PMID: 38855310 PMCID: PMC11157109 DOI: 10.3389/fpsyg.2024.1303372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 05/13/2024] [Indexed: 06/11/2024] Open
Abstract
Introduction The Male Warrior Hypothesis (MWH) proposes that sex-specific selective pressures have promoted male cooperation with the ingroup members to outcompete rival groups. However, intergroup conflicts do not occur in isolation and the outcomes of previous competitions may influence group cooperativeness. Since this phenomenon is not well understood, we aimed to shed light on the effect of previous competition outcome on later cooperative behavior under intergroup conflicts. Based on the MWH, we hypothesized that repeated contests between groups could enhance ingroup cooperation, regardless of the outcome of the previous contest because status is at risk, but when competition is not present, participants would move to the symmetric equilibria. Methods To test this hypothesis, we recruited 246 individuals organized in groups of 6 and measured cooperation using a threshold public good game over two rounds, manipulating the outcome in the first round to create groups of winners and losers. Results Our results show that intergroup conflict scenarios promoted cooperation in both victory and defeat conditions, whereas, in the control scenario only losers increased their cooperation. Discussion We argue that winners under the presence of an external threat may enhance in-group cooperation in order to assure their status; whereas, losers may be attempting to regain it.
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Affiliation(s)
- Montserrat Belinchón
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - Pablo Polo
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - Carlos Rodriguez-Sickert
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - Oriana Figueroa
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - Nohelia Valenzuela
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - Paula Pavez
- Facultad de Educación, Universidad San Sebastián, Santiago, Chile
| | - José Antonio Muñoz-Reyes
- Laboratorio de Comportamiento Animal y Humano, Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
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Guyon L, Guez J, Toupance B, Heyer E, Chaix R. Patrilineal segmentary systems provide a peaceful explanation for the post-Neolithic Y-chromosome bottleneck. Nat Commun 2024; 15:3243. [PMID: 38658560 PMCID: PMC11043392 DOI: 10.1038/s41467-024-47618-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Accepted: 04/08/2024] [Indexed: 04/26/2024] Open
Abstract
Studies have found a pronounced decline in male effective population sizes worldwide around 3000-5000 years ago. This bottleneck was not observed for female effective population sizes, which continued to increase over time. Until now, this remarkable genetic pattern was interpreted as the result of an ancient structuring of human populations into patrilineal groups (gathering closely related males) violently competing with each other. In this scenario, violence is responsible for the repeated extinctions of patrilineal groups, leading to a significant reduction in male effective population size. Here, we propose an alternative hypothesis by modelling a segmentary patrilineal system based on anthropological literature. We show that variance in reproductive success between patrilineal groups, combined with lineal fission (i.e., the splitting of a group into two new groups of patrilineally related individuals), can lead to a substantial reduction in the male effective population size without resorting to the violence hypothesis. Thus, a peaceful explanation involving ancient changes in social structures, linked to global changes in subsistence systems, may be sufficient to explain the reported decline in Y-chromosome diversity.
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Affiliation(s)
- Léa Guyon
- Eco-Anthropologie (UMR 7206), Muséum National d'Histoire Naturelle, CNRS, Université Paris Cité, Paris, 75116, France.
| | - Jérémy Guez
- Eco-Anthropologie (UMR 7206), Muséum National d'Histoire Naturelle, CNRS, Université Paris Cité, Paris, 75116, France
- Université Paris-Saclay, CNRS, INRIA, Laboratoire Interdisciplinaire des Sciences du Numérique, Orsay, 91400, France
| | - Bruno Toupance
- Eco-Anthropologie (UMR 7206), Muséum National d'Histoire Naturelle, CNRS, Université Paris Cité, Paris, 75116, France
- Université Paris Cité, Eco-anthropologie, Paris, F-75006, France
| | - Evelyne Heyer
- Eco-Anthropologie (UMR 7206), Muséum National d'Histoire Naturelle, CNRS, Université Paris Cité, Paris, 75116, France
| | - Raphaëlle Chaix
- Eco-Anthropologie (UMR 7206), Muséum National d'Histoire Naturelle, CNRS, Université Paris Cité, Paris, 75116, France.
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3
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Ross CT, Hooper PL, Smith JE, Jaeggi AV, Smith EA, Gavrilets S, Zohora FT, Ziker J, Xygalatas D, Wroblewski EE, Wood B, Winterhalder B, Willführ KP, Willard AK, Walker K, von Rueden C, Voland E, Valeggia C, Vaitla B, Urlacher S, Towner M, Sum CY, Sugiyama LS, Strier KB, Starkweather K, Major-Smith D, Shenk M, Sear R, Seabright E, Schacht R, Scelza B, Scaggs S, Salerno J, Revilla-Minaya C, Redhead D, Pusey A, Purzycki BG, Power EA, Pisor A, Pettay J, Perry S, Page AE, Pacheco-Cobos L, Oths K, Oh SY, Nolin D, Nettle D, Moya C, Migliano AB, Mertens KJ, McNamara RA, McElreath R, Mattison S, Massengill E, Marlowe F, Madimenos F, Macfarlan S, Lummaa V, Lizarralde R, Liu R, Liebert MA, Lew-Levy S, Leslie P, Lanning J, Kramer K, Koster J, Kaplan HS, Jamsranjav B, Hurtado AM, Hill K, Hewlett B, Helle S, Headland T, Headland J, Gurven M, Grimalda G, Greaves R, Golden CD, Godoy I, Gibson M, Mouden CE, Dyble M, Draper P, Downey S, DeMarco AL, Davis HE, Crabtree S, Cortez C, Colleran H, Cohen E, Clark G, Clark J, Caudell MA, Carminito CE, Bunce J, Boyette A, Bowles S, Blumenfield T, Beheim B, Beckerman S, Atkinson Q, Apicella C, Alam N, Mulder MB. Reproductive inequality in humans and other mammals. Proc Natl Acad Sci U S A 2023; 120:e2220124120. [PMID: 37216525 PMCID: PMC10235947 DOI: 10.1073/pnas.2220124120] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Accepted: 04/16/2023] [Indexed: 05/24/2023] Open
Abstract
To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.
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Affiliation(s)
- Cody T. Ross
- Santa Fe Institute, Santa Fe, NM87501
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Paul L. Hooper
- Santa Fe Institute, Santa Fe, NM87501
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
| | | | - Adrian V. Jaeggi
- Institut für Anthropologie und Anthropologisches Museum, University of Zürich, Zürich8006, Switzerland
| | - Eric Alden Smith
- Department of Anthropology, University of Washington, Seattle, WA98195
| | - Sergey Gavrilets
- Departments of Ecology and Evolutionary Biology and Mathematics, University of Tennessee, Knoxville, TN37996
| | - Fatema tuz Zohora
- International Centre for Diarrheal Disease Research, Dhaka1000, Bangladesh
| | - John Ziker
- Department of Anthropology, Boise State University, Boise, ID83725
| | | | | | - Brian Wood
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of Anthropology, University of California, Los Angeles, CA90095
| | | | - Kai P. Willführ
- Institute for Social Science, University of Oldenburg, Oldenburg26129, Germany
| | - Aiyana K. Willard
- Centre for Culture and Evolution, Brunel University, LondonUB8 3PH, United Kingdom
| | - Kara Walker
- College of Veterinary Medicine, North Carolina State University, Raleigh, NC27695
| | | | - Eckart Voland
- Institute for Philosophy, Justus-Liebig University, Giessen35390, Germany
| | | | - Bapu Vaitla
- Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, MA02115
| | - Samuel Urlacher
- Department of Anthropology, Baylor University, Waco, TX76706
- Canadian Institute for Advanced Research, Toronto, CAM5G 1M1
| | - Mary Towner
- Department of Integrative Biology, Oklahoma State University, Stillwater, OK74078
| | - Chun-Yi Sum
- College of General Studies, Boston University, Boston, MA02215
| | | | - Karen B. Strier
- Department of Zoology, University of Wisconsin, Madison, WI53706
| | | | - Daniel Major-Smith
- Department of Anthropology and Archaeology, University of Bristol, BristolBS8 1QU, United Kingdom
| | - Mary Shenk
- Department of Anthropology, Pennsylvania State University, University Park, PA16802
| | - Rebecca Sear
- Department of Population Health, London School of Hygiene and Tropical Medicine, LondonWC1E 7HT, United Kingdom
| | - Edmond Seabright
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
| | - Ryan Schacht
- Department of Anthropology, East Carolina University, Greenville, NC27858
| | - Brooke Scelza
- Department of Anthropology, University of California, Los Angeles, CA90095
| | - Shane Scaggs
- Department of Anthropology, Ohio State University, Columbus, OH43210
| | - Jonathan Salerno
- Department of Human Dimensions of Natural Resources, Colorado State University, Fort Collins, CO80523
| | - Caissa Revilla-Minaya
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Daniel Redhead
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Anne Pusey
- Department of Evolutionary Anthropology, Duke University, Durham, NC27708
| | - Benjamin Grant Purzycki
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of the Study of Religion, Aarhus University, Aarhus8000, Denmark
| | - Eleanor A. Power
- Santa Fe Institute, Santa Fe, NM87501
- Department of Methodology, London School of Economics and Political Science, LondonWC2A 2AE, United Kingdom
| | - Anne Pisor
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of Anthropology, Washington State University, Pullman, WA99164
| | - Jenni Pettay
- Department of Biology, University of Turku, Turku20014, Finland
| | - Susan Perry
- Department of Anthropology, University of California, Los Angeles, CA90095
| | - Abigail E. Page
- Department of Population Health, London School of Hygiene and Tropical Medicine, LondonWC1E 7HT, United Kingdom
| | - Luis Pacheco-Cobos
- Facultad de Ciencias Biológicas y Agropecuarias, Universidad Veracruzana, Veracruz94294, Mexico
| | - Kathryn Oths
- Department of Anthropology, University of Alabama, Tuscaloosa, AL35487
| | - Seung-Yun Oh
- Korea Insurance Research Institute, Seoul150-606, Korea
| | - David Nolin
- Department of Sociology, University of Massachusetts, Amherst, MA01003
| | - Daniel Nettle
- Département d’Etudes Cognitives, Ecole Normale Supérieure, Université PSL, Paris75230, France
| | - Cristina Moya
- Department of Anthropology, University of California, Davis, CA95616
| | - Andrea Bamberg Migliano
- Institut für Anthropologie und Anthropologisches Museum, University of Zürich, Zürich8006, Switzerland
| | - Karl J. Mertens
- Department of Anthropology, Boise State University, Boise, ID83725
| | - Rita A. McNamara
- School of Psychology, Victoria University of Wellington, Wellington6012, New Zealand
| | - Richard McElreath
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Siobhan Mattison
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
| | - Eric Massengill
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
| | - Frank Marlowe
- Department of Biological Anthropology, University of Cambridge, CambridgeCB2 1TN, United Kingdom
| | - Felicia Madimenos
- Department of Anthropology, Queens College (CUNY), New York, NY11367
| | - Shane Macfarlan
- Department of Anthropology, University of Utah, Salt Lake City, UT84112
| | - Virpi Lummaa
- Department of Biology, University of Turku, Turku20014, Finland
| | - Roberto Lizarralde
- Facultad de Ciencias Económicas y Sociales, Universidad Central de Venezuela, Caracas1010A, Venezuela
| | - Ruizhe Liu
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
| | - Melissa A. Liebert
- Department of Anthropology, Northern Arizona University, Flagstaff, AZ86011
| | - Sheina Lew-Levy
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of Psychology, Durham University, DurhamDH1 3LE, United Kingdom
| | - Paul Leslie
- Department of Anthropology, University of North Carolina, Chapel Hill, NC27599
| | | | - Karen Kramer
- Department of Anthropology, University of Utah, Salt Lake City, UT84112
| | - Jeremy Koster
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of Biological Sciences, University of Cincinnati, Cincinnati, OH45221
| | | | | | - A. Magdalena Hurtado
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ85287
| | - Kim Hill
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ85287
| | - Barry Hewlett
- Department of Anthropology, Washington State University, Pullman, WA99164
| | - Samuli Helle
- Department of Biology, University of Turku, Turku20014, Finland
| | | | | | - Michael Gurven
- Department of Anthropology, University of California, Santa Barbara, CA93106
| | | | - Russell Greaves
- Department of Anthropology, University of Utah, Salt Lake City, UT84112
| | - Christopher D. Golden
- Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, MA02115
| | - Irene Godoy
- Department of Animal Behaviour, Bielefeld University, Bielefeld33615, Germany
| | - Mhairi Gibson
- Department of Anthropology and Archaeology, University of Bristol, BristolBS8 1QU, United Kingdom
| | - Claire El Mouden
- School of Anthropology and Museum Ethnography, University of Oxford, OxfordOX1 2JD, United Kingdom
| | - Mark Dyble
- Department of Anthropology, University College London, LondonWC1E 6BT, United Kingdom
| | - Patricia Draper
- School of Global Integrative Studies, University of Nebraska, Lincoln, NE68588
| | - Sean Downey
- Department of Anthropology, Ohio State University, Columbus, OH43210
| | | | | | - Stefani Crabtree
- Santa Fe Institute, Santa Fe, NM87501
- Department of Environment and Society, Utah State University, Logan, UT84322
| | - Carmen Cortez
- Department of Anthropology, University of California, Davis, CA95616
| | - Heidi Colleran
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Emma Cohen
- School of Anthropology and Museum Ethnography, University of Oxford, OxfordOX1 2JD, United Kingdom
| | - Gregory Clark
- Department of Economics, University of California, Davis, CA95616
| | | | - Mark A. Caudell
- Department of Anthropology, Washington State University, Pullman, WA99164
| | - Chelsea E. Carminito
- Department of Biological Sciences, University of Cincinnati, Cincinnati, OH45221
| | - John Bunce
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Adam Boyette
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | | | - Tami Blumenfield
- Department of Anthropology, University of New Mexico, Albuquerque, NM87131
- School of Ethnology and Sociology, Yunnan University, Yunnan650106, China
| | - Bret Beheim
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
| | - Stephen Beckerman
- Department of Anthropology, Pennsylvania State University, University Park, PA16802
| | - Quentin Atkinson
- School of Psychology, University of Auckland, Auckland1010, New Zealand
| | - Coren Apicella
- Department of Psychology, University of Pennsylvania, Philadelphia, PA19104
| | - Nurul Alam
- International Centre for Diarrheal Disease Research, Dhaka1000, Bangladesh
| | - Monique Borgerhoff Mulder
- Santa Fe Institute, Santa Fe, NM87501
- Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig04103, Germany
- Department of Anthropology, University of California, Davis, CA95616
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Historical and hunter-gatherer perspectives on fast-slow life history strategies. EVOL HUM BEHAV 2023. [DOI: 10.1016/j.evolhumbehav.2023.02.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
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Hackman J, Kramer KL. Kin networks and opportunities for reproductive cooperation and conflict among hunter-gatherers. Philos Trans R Soc Lond B Biol Sci 2023; 378:20210434. [PMID: 36440562 PMCID: PMC9703223 DOI: 10.1098/rstb.2021.0434] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 10/03/2022] [Indexed: 11/29/2022] Open
Abstract
Little is known about the potential for reproductive conflict among hunter-gatherer populations, who are characterized by bilateral kinship ties, flexible residential mobility, and high offspring mortality. To assess the potential for reproductive conflict, we use longitudinal residence and reproductive history data for two bands of South American foragers. Using multilevel logistic regressions (N = 44 women, N = 712 person years), we examine how yearly measures of (i) camp composition, (ii) distribution of female kin and (iii) a woman's position in a female kinship network impact the likelihood of giving birth or experiencing a child's death. We compare conflict models to a demographic model that accounts for the proportion of women giving birth in a given year. Contrary to conflict models, results show that the odds of giving birth increase with the presence of highly related women. However, the odds of experiencing an offspring death are insensitive to the presence of coresident women. Network measures of closeness and centrality in the female kin network also show no significant effect on reproductive outcomes. Furthermore, chances of both births and deaths increase in years when proportionally more women are giving birth. We argue that demographic stochasticity relating to ecological conditions best predicts reproductive outcomes for women. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.
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Affiliation(s)
- Joseph Hackman
- Department of Anthropology, University of Utah, Salt Lake City, UT 84112, USA
| | - Karen L. Kramer
- Department of Anthropology, University of Utah, Salt Lake City, UT 84112, USA
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6
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Daly M. Inequality, grievances, and the variability in homicide rates. EVOL HUM BEHAV 2023. [DOI: 10.1016/j.evolhumbehav.2023.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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7
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Understanding the sex inequality in childlessness: an approach using Swedish register data. J Biosoc Sci 2023; 55:99-115. [PMID: 36515091 DOI: 10.1017/s0021932021000638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In most countries, men are more likely to be childless than women. Understanding how this inequality arises is important given the significance of parenthood for individuals' lives. The objective of this study was to explore how three prominent explanations for sex inequalities in childlessness relate to the Sex Gap in Childlessness (SGC) in Sweden. The three explanations examined were sex ratio imbalance (more men than women), mismeasurement of fatherhood (inequalities in registration) and partnership differences (inequality in multi-partner fertility). Administrative register data for cohorts born in 1945-1974 were used. The population was restricted to men and women who were born in Sweden or arrived prior to the age of 15, and all registered childbearing partnerships were examined. To explore the possible significance of the three explanations, counter-factual standardization was used. Of the three explanations examined, the population sex ratio had the largest positive impact on the SGC, while multi-partner fertility had a negative impact. The results show that inequalities in the sex ratio can explain about 20-34% of the SGC depending on cohort. Inequalities in registration of fathers explain about 9-24% of the SGC depending on cohort. Finally, results show that women are slightly more likely to have multiple partners, and that this behaviour has a substantial minimizing effect on the SGC (minimizing it by 6-65%). To the authors' knowledge this was the first paper to estimate the scope of the impacts of these three mechanisms on the SGC. Differences in multi-partner fertility have in many instances been used as an explanation for men's higher childlessness. This study shows that women have slightly more childbearing partners than men, and that this actually leads to a smaller SGC in the studied population.
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Variability in energy expenditure is much greater in males than females. J Hum Evol 2022; 171:103229. [PMID: 36115145 PMCID: PMC9791915 DOI: 10.1016/j.jhevol.2022.103229] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 06/01/2022] [Accepted: 06/12/2022] [Indexed: 11/24/2022]
Abstract
In mammals, trait variation is often reported to be greater among males than females. However, to date, mainly only morphological traits have been studied. Energy expenditure represents the metabolic costs of multiple physical, physiological, and behavioral traits. Energy expenditure could exhibit particularly high greater male variation through a cumulative effect if those traits mostly exhibit greater male variation, or a lack of greater male variation if many of them do not. Sex differences in energy expenditure variation have been little explored. We analyzed a large database on energy expenditure in adult humans (1494 males and 3108 females) to investigate whether humans have evolved sex differences in the degree of interindividual variation in energy expenditure. We found that, even when statistically comparing males and females of the same age, height, and body composition, there is much more variation in total, activity, and basal energy expenditure among males. However, with aging, variation in total energy expenditure decreases, and because this happens more rapidly in males, the magnitude of greater male variation, though still large, is attenuated in older age groups. Considerably greater male variation in both total and activity energy expenditure could be explained by greater male variation in levels of daily activity. The considerably greater male variation in basal energy expenditure is remarkable and may be explained, at least in part, by greater male variation in the size of energy-demanding organs. If energy expenditure is a trait that is of indirect interest to females when choosing a sexual partner, this would suggest that energy expenditure is under sexual selection. However, we present a novel energetics model demonstrating that it is also possible that females have been under stabilizing selection pressure for an intermediate basal energy expenditure to maximize energy available for reproduction.
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Rucas SL, Alami S. Female-Female Competition Occurs Irrespective of Patrilocality. ARCHIVES OF SEXUAL BEHAVIOR 2022; 51:3287-3292. [PMID: 34799834 DOI: 10.1007/s10508-021-02221-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 11/05/2021] [Accepted: 11/06/2021] [Indexed: 06/13/2023]
Affiliation(s)
- Stacey L Rucas
- Department of Social Sciences, California Polytechnic State University, 1 Grand Avenue, San Luis Obispo, CA, 93407-0329, USA.
| | - Sarah Alami
- Department of Anthropology, University of California, Santa Barbara, CA, USA
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The Cocksure Conundrum: How Evolution Created a Gendered Currency of Corporate Overconfidence. ADAPTIVE HUMAN BEHAVIOR AND PHYSIOLOGY 2022. [DOI: 10.1007/s40750-022-00197-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Abstract
AbstractBiological differences between men and women mandate that women’s obligatory investment in reproduction is significantly greater than that of men. As a result, women have evolved to be the “choosier” of the two sexes and men have evolved to compete for female choice. To the degree that overconfidence is an effective tool for attracting mates and driving away competitors, greater competition among men suggests that they should express more overconfidence than women. Thus, sexual selection may be the primary reason why overconfidence is typically more pronounced in men than it is in women. Sexual selection may also be a distal, causal factor in what we describe as a cult of overconfidence pervading modern organizations and institutions. Whereas overconfidence was once regulated and constrained by features of ancestral life, levels of social mobility and accountability in contemporary society and modern organizations make it increasingly difficult to keep this gendered bias in check.
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Zhang Y, Santtila P. Social status predicts different mating and reproductive success for men and women in China: evidence from the 2010–2017 CGSS data. Behav Ecol Sociobiol 2022. [DOI: 10.1007/s00265-022-03209-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Abstract
Evolutionary psychological theories posit that higher social status is conducive to men’s reproductive success. Extant research from historical records, small scale societies, as well as industrialized societies, support this hypothesis. However, the relationship between status difference between spouses and reproductive success has been investigated less. Moreover, even fewer studies have directly compared the effect of status and status difference between spouses on reproductive success in men and women. Using data from the Chinese General Social Survey (CGSS) conducted between 2010 and 2017 (N = 55,875; 28,931 women) and operationalizing social status as standardized income and educational level (compared with same-sex peers), we examined how social status and relative status between spouses impact men’s and women’s mating and reproductive success. We found that (1) men with higher social status were more likely to have long-term mating (being in a marriage and/or not going through marriage disruption) and reproductive success, mainly through having a lower risk of childlessness; (2) women with higher social status were less likely to have mating and reproductive success; and (3) relative status between spouses had an impact on the couple’s reproductive success so that couples, where the husband had higher status compared to the wife, had higher reproductive success. Thus, social status positively impacted men’s reproductive success, but relative status between spouses also affected mating and impacted childbearing decisions.
Significance statement
In terms of standardized educational level and income among peers, social status positively predicts men’s mating and reproductive success in contemporary China. However, while a higher social status increases the probability of having at least one child, it does not predict a greater number of children for men. A status difference between spouses, on the other hand, consistently predicts having children. Thus, the higher the husband’s status relative to his wife, the greater the likelihood of having the first, second, and third children. The current results suggest that when examining the effect of status on mating and reproduction, social status and status within a family should be considered. We also stress the importance of exploring the potential proximate mechanisms by which a status difference influences childbearing decisions.
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12
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Li L, Jiang H. Development of Fertility, Social Status, and Social Trust of Farmers. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19084759. [PMID: 35457627 PMCID: PMC9027793 DOI: 10.3390/ijerph19084759] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 04/09/2022] [Accepted: 04/12/2022] [Indexed: 02/01/2023]
Abstract
Fertility, social status, and social trust are main social choice behaviors of Chinese farmers. This paper adopts the childbearing–value logic to establish a theoretical model of farmers’ childbearing–social status–social trust choices to examine the influence of farmers’ childbearing and social status on farmers’ social trust. The theoretical model showed that farmers will rationally choose the number of children to bear, emotional value, social value, economic value, social status, and social trust. The fertility of farmers’ children is actually a trade-off between quantity and value, and the fertility behavior affects social status through the direct mechanism of the number of children and the value of the adjustment mechanism, and together with the social status, through the direct mechanism, the adjustment mechanism of the number of children, the intermediate mechanism of social status, and the mixed adjustment mechanism. Asymmetry affects social trust equilibrium. Empirical research based on the CFPS (China Family Panel Studies) data in 2018 showed that farmers’ children quantity primarily inhibits, through the adjustment mechanism of children’s value–social status, social status and social trust; it exerts no direct impact or mediating effect on the social status. The economic value of children does not affect the social status, but it affects social trust through a positive child quantity adjustment mechanism, a negative social status mediation mechanism, and a negative mixed mediation mechanism. The social value of children affects social trust by the positive direct mechanism and the negative children quantity adjustment mechanism, as well as social trust by the negative direct mechanism, children quantity adjustment mechanism, children quantity–social status mixed adjustment mediating mechanism, and the positive social status–mediated mechanism. The emotional value of children affects the social status through the positive direct mechanism, as well as social trust through the positive direct mechanism, social status–mediated mechanism, and negative child quantity adjustment mechanism, and negative mixed mediation mechanism. Furthermore, social status positively impacts social trust rather than a symmetric transmission of the mediating effect of children’s value and the quantity adjustment effect of children’s value. However, no mediating effect of social trust was observed on children quantity. Social development leads to structural changes in the fertility value of farmers’ children, which makes farmers prefer their children’s social and economic value, exerting a complex impact on their own social status and social trust.
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13
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Gardner EJ, Neville MDC, Samocha KE, Barclay K, Kolk M, Niemi MEK, Kirov G, Martin HC, Hurles ME. Reduced reproductive success is associated with selective constraint on human genes. Nature 2022; 603:858-863. [PMID: 35322230 DOI: 10.1038/s41586-022-04549-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 02/07/2022] [Indexed: 12/22/2022]
Abstract
Genome-wide sequencing of human populations has revealed substantial variation among genes in the intensity of purifying selection acting on damaging genetic variants1. Although genes under the strongest selective constraint are highly enriched for associations with Mendelian disorders, most of these genes are not associated with disease and therefore the nature of the selection acting on them is not known2. Here we show that genetic variants that damage these genes are associated with markedly reduced reproductive success, primarily owing to increased childlessness, with a stronger effect in males than in females. We present evidence that increased childlessness is probably mediated by genetically associated cognitive and behavioural traits, which may mean that male carriers are less likely to find reproductive partners. This reduction in reproductive success may account for 20% of purifying selection against heterozygous variants that ablate protein-coding genes. Although this genetic association may only account for a very minor fraction of the overall likelihood of being childless (less than 1%), especially when compared to more influential sociodemographic factors, it may influence how genes evolve over time.
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Affiliation(s)
- Eugene J Gardner
- Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, Hinxton, UK.,Medical Research Council (MRC) Epidemiology Unit, University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, UK
| | | | - Kaitlin E Samocha
- Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, Hinxton, UK
| | - Kieron Barclay
- Max Planck Institute for Demographic Research, Rostock, Germany.,Demography Unit, Department of Sociology, Stockholm University, Stockholm, Sweden.,Swedish Collegium for Advanced Study, Uppsala, Sweden
| | - Martin Kolk
- Demography Unit, Department of Sociology, Stockholm University, Stockholm, Sweden
| | - Mari E K Niemi
- Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, Hinxton, UK
| | - George Kirov
- Division of Psychological Medicine and Clinical Neurosciences, School of Medicine, Cardiff University, Cardiff, UK
| | - Hilary C Martin
- Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, Hinxton, UK
| | - Matthew E Hurles
- Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, Hinxton, UK.
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14
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Konner M. Is History the Same as Evolution? No. Is it Independent of Evolution? Certainly Not. EVOLUTIONARY PSYCHOLOGY 2022; 20:14747049211069137. [PMID: 35253457 PMCID: PMC10523472 DOI: 10.1177/14747049211069137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 12/08/2021] [Accepted: 12/08/2021] [Indexed: 11/15/2022] Open
Abstract
History is full of violence and oppression within and between groups, and although group conflicts enhance within-group cooperation (mediated by oxytocin, which promotes parochial altruism) the hierarchy within groups ensures that spoils accrue very unevenly. Darwin suggested, and we now know, that sexual selection is as powerful as selection by mortality, and the main purpose of survival is reproduction. Male reproductive skew is greater than that among females in all societies, but the difference became much greater after the hunting-gathering era, and the rise of so-called "civilization" was everywhere a process of predatory expansion, producing kingdoms and empires where top males achieved astounding heights of reproductive success. This was shown by historical and ethnographic data now strongly confirmed by genomic science. Psychological research confirms that group identity, out-group stigmatization, leadership characterized by charisma, the will to power, narcissism, sociopathy, and cruelty, and followership characterized by hypnotic obedience, loss of individuality, and cruelty are integral parts of human nature. We can thank at least ten or twelve millennia of microevolutionary processes such as those described above, all more prominent in males than females. Followers in wars have faced a difficult risk-benefit analysis, but if they survived and won they too could increase their reproductive success through the rape and other sexual exploitation that have accompanied almost all wars. For modern leaders, social monogamy and contraception have separated autocracy from reproductive success, but only partly, and current worldwide autocratic trends still depend on the evolved will to power, obedience, and cruelty.
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Affiliation(s)
- Melvin Konner
- Department of Anthropology, Program in Neuroscience & Behavioral Biology, Atlanta, Georgia, USA
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15
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Geary DC. Spatial ability as a distinct domain of human cognition: An evolutionary perspective. INTELLIGENCE 2022. [DOI: 10.1016/j.intell.2021.101616] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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16
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Nine Levels of Explanation : A Proposed Expansion of Tinbergen's Four-Level Framework for Understanding the Causes of Behavior. HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE 2021; 32:748-793. [PMID: 34739657 DOI: 10.1007/s12110-021-09414-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/23/2021] [Indexed: 01/16/2023]
Abstract
Tinbergen's classic "On Aims and Methods of Ethology" (Zeitschrift für Tierpsychologie, 20, 1963) proposed four levels of explanation of behavior, which he thought would soon apply to humans. This paper discusses the need for multilevel explanation; Huxley and Mayr's prior models, and others that followed; Tinbergen's differences with Lorenz on "the innate"; and Mayr's ultimate/proximate distinction. It synthesizes these approaches with nine levels of explanation in three categories: phylogeny, natural selection, and genomics (ultimate causes); maturation, sensitive period effects, and routine environmental effects (intermediate causes); and hormonal/metabolic processes, neural circuitry, and eliciting stimuli (proximate causes), as a respectful extension of Tinbergen's levels. The proposed classification supports and builds on Tinbergen's multilevel model and Mayr's ultimate/proximate continuum, adding intermediate causes in accord with Tinbergen's emphasis on ontogeny. It requires no modification of Standard Evolutionary Theory or The Modern Synthesis, but shows that much that critics claim was missing was in fact part of Neo-Darwinian theory (so named by J. Mark Baldwin in The American Naturalist in 1896) all along, notably reciprocal causation in ontogeny, niche construction, cultural evolution, and multilevel selection. Updates of classical examples in ethology are offered at each of the nine levels, including the neuroethological and genomic findings Tinbergen foresaw. Finally, human examples are supplied at each level, fulfilling his hope of human applications as part of the biology of behavior. This broad ethological framework empowers us to explain human behavior-eventually completely-and vindicates the idea of human nature, and of humans as a part of nature.
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17
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Agey E, Morris A, Chandy M, Gaulin SJC. Arranged Marriage Often Subverts Offspring Mate Choice: An HRAF‐Based Study. AMERICAN ANTHROPOLOGIST 2021. [DOI: 10.1111/aman.13656] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Elizabeth Agey
- Department of Anthropology University of California Santa Barbara USA
| | - Addison Morris
- Department of Anthropology University of California Santa Barbara USA
| | - Maya Chandy
- Department of Anthropology University of California Santa Barbara USA
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18
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Scheidel W. Fitness and Power: The Contribution of Genetics to the History of Differential Reproduction. EVOLUTIONARY PSYCHOLOGY 2021; 19:14747049211066599. [PMID: 34918580 PMCID: PMC10303451 DOI: 10.1177/14747049211066599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Accepted: 11/28/2021] [Indexed: 11/16/2022] Open
Abstract
Textual evidence from pre-modern societies supports the prediction that status differences among men translate to variance in reproductive success. In recent years, analysis of genetic data has opened up new ways of studying this relationship. By investigating cases that range over several millennia, these analyses repeatedly document the replacement of local men by newcomers and reveal instances of exceptional reproductive success of specific male lineages. These findings suggest that violent population transfers and conquests could generate considerable reproductive advantages for male dominants. At the same time, this does not always seem to have been the case. Moreover, it is difficult to link such outcomes to particular historical characters or events, or to identify status-biased reproductive inequalities within dominant groups. The proximate factors that mediated implied imbalances in reproductive success often remain unclear. A better understanding of the complex interplay between social power and genetic fitness will only arise from sustained transdisciplinary engagement.
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19
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Betzig L. A Note on Religion. EVOLUTIONARY PSYCHOLOGY 2021; 19:14747049211066795. [PMID: 34939448 PMCID: PMC10303561 DOI: 10.1177/14747049211066795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Accepted: 11/29/2021] [Indexed: 11/17/2022] Open
Abstract
At the beginning of our era, after a battle on the Ionian Sea, Antony and Cleopatra took their own lives in Egypt, and Augustus was made an imperator by his senators. Roman emperors had sexual access to those senators' daughters and wives, and to thousands of slaves. But they ran governments with help from their cubicularii, castrated civil servants. And they enforced an Imperial Cult: subjects made sacrifices to the emperor's genius, or procreative spirit; or they got disemboweled by wild animals, or decapitated. Then Constantine moved off from the Tiber to the Bosporus, and Europe was ruled over by a few. Lords covered the countryside with bastards, but passed on estates on to their oldest sons. Daughters and younger sons were put away in the Church, where some became parents, but most were reproductively suppressed: they were ἄνανδρος or anandros, or without a husband, and ἄγαμος or agamos, or without a wife. Heretics who objected got burned at the stake. Then the Crusaders expanded Europe to the East, and Columbus went off to the West, and politics, sex and religion became more democratic. Power was more widely distributed; more men and women had families if they wanted them, and monasteries emptied out. The Reformation followed the Roman Church, which had followed the Imperial Cult.
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Affiliation(s)
- Laura Betzig
- Evolutionary Psychology: Human History as
Natural History
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20
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Smith JE, von Rueden CR, van Vugt M, Fichtel C, Kappeler PM. An Evolutionary Explanation for the Female Leadership Paradox. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.676805] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Social influence is distributed unequally between males and females in many mammalian societies. In human societies, gender inequality is particularly evident in access to leadership positions. Understanding why women historically and cross-culturally have tended to be under-represented as leaders within human groups and organizations represents a paradox because we lack evidence that women leaders consistently perform worse than men. We also know that women exercise overt influence in collective group-decisions within small-scale human societies, and that female leadership is pervasive in particular contexts across non-human mammalian societies. Here, we offer a transdisciplinary perspective on this female leadership paradox. Synthesis of social science and biological literatures suggests that females and males, on average, differ in why and how they compete for access to political leadership in mixed-gender groups. These differences are influenced by sexual selection and are moderated by socioecological variation across development and, particularly in human societies, by culturally transmitted norms and institutions. The interplay of these forces contributes to the emergence of female leaders within and across species. Furthermore, females may regularly exercise influence on group decisions in less conspicuous ways and different domains than males, and these underappreciated forms of leadership require more study. We offer a comprehensive framework for studying inequality between females and males in access to leadership positions, and we discuss the implications of this approach for understanding the female leadership paradox and for redressing gender inequality in leadership in humans.
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21
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Geary DC. Evolution and Sex Differences in Political Engagement. PSYCHOLOGICAL INQUIRY 2021. [DOI: 10.1080/1047840x.2021.1930766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- David C. Geary
- Department of Psychological Sciences, University of Missouri, Columbia, Missouri, USA
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22
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Life History Theory: Evolutionary mechanisms and gender role on risk-taking behaviors in young adults. PERSONALITY AND INDIVIDUAL DIFFERENCES 2021. [DOI: 10.1016/j.paid.2021.110752] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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23
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Geary DC. Now you see them, and now you don't: An evolutionarily informed model of environmental influences on human sex differences. Neurosci Biobehav Rev 2021; 125:26-32. [PMID: 33609571 DOI: 10.1016/j.neubiorev.2021.02.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 08/05/2020] [Accepted: 02/10/2021] [Indexed: 11/13/2022]
Abstract
The contributions of evolutionary processes to human sex differences are vigorously debated. One counterargument is that the magnitude of many sex differences fluctuates from one context to the next, implying an environment origin. Sexual selection provides a framework for integrating evolutionary processes and environmental influences on the origin and magnitude of sex differences. The dynamics of sexual selection involve competition for mates and discriminative mate choices. The associated traits are typically exaggerated and condition-dependent, that is, their development and expression are very sensitive to social and ecological conditions. The magnitude of sex differences in sexually selected traits should then be largest under optimal social and ecological conditions and shrink as conditions deteriorate. The basics of this framework are described, and its utility is illustrated with discussion of fluctuations in the magnitude of human physical, behavioral, and cognitive sex differences.
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Affiliation(s)
- David C Geary
- Department of Psychological Sciences, Interdisciplinary Neuroscience, University of Missouri, Columbia, MO, 65211-2500, United States.
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24
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Bribiescas RG. Evolutionary and Life History Insights into Masculinity and Warfare. CURRENT ANTHROPOLOGY 2021. [DOI: 10.1086/711688] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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25
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Stewart-Williams S, Halsey LG. Men, women and STEM: Why the differences and what should be done? EUROPEAN JOURNAL OF PERSONALITY 2021. [DOI: 10.1177/0890207020962326] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
It is a well-known and widely lamented fact that men outnumber women in a number of fields in STEM (science, technology, engineering and maths). The most commonly discussed explanations for the gender gaps are discrimination and socialization, and the most common policy prescriptions target those ostensible causes. However, a great deal of evidence in the behavioural sciences suggests that discrimination and socialization are only part of the story. The purpose of this paper is to highlight other aspects of the story: aspects that are commonly overlooked or downplayed. More precisely, the paper has two main aims. The first is to examine the evidence that factors other than workplace discrimination contribute to the gender gaps in STEM. These include relatively large average sex differences in career and lifestyle preferences, and relatively small average differences in cognitive aptitudes – some favouring males, others favouring females – which are associated with progressively larger differences the further above the average one looks. The second aim is to examine the evidence suggesting that these sex differences are not purely a product of social factors but also have a substantial biological (i.e. inherited) component. A more complete picture of the causes of the unequal sex ratios in STEM may productively inform policy discussions.
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Affiliation(s)
| | - Lewis G Halsey
- Department of Life Sciences, University of Roehampton, London, UK
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26
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Gettler LT, Boyette AH, Rosenbaum S. Broadening Perspectives on the Evolution of Human Paternal Care and Fathers’ Effects on Children. ANNUAL REVIEW OF ANTHROPOLOGY 2020. [DOI: 10.1146/annurev-anthro-102218-011216] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Unlike most mammals, human fathers cooperate with mothers to care for young to an extraordinary degree. Human paternal care likely evolved alongside our unique life history strategy of raising slow-developing, energetically costly children, often in rapid succession. Adaptive frameworks generally assume that paternal provisioning played a critical role in this pattern's emergence. We draw on nonhuman primate data to propose that nonprovisioning forms of low-cost hominin male care were potentially foundational and ratcheted up through evolutionary time, helping facilitate social contexts for later subsistence specialization and sharing. We then argue for expanding the breadth of anthropological research on paternal effects in families, particularly in three domains: direct care and teaching;social capital cultivation; and reduction of family conflict. Anthropologists can greatly contribute to conversations about the determinants of children's development across contexts, but we need to ask more expansive questions about the pathways through which caregivers (including fathers) affect child outcomes.
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Affiliation(s)
- Lee T. Gettler
- Department of Anthropology, and Eck Institute for Global Health, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Adam H. Boyette
- Department of Human Behavior, Ecology, and Culture, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany
| | - Stacy Rosenbaum
- Department of Anthropology, University of Michigan, Ann Arbor, Michigan 48109, USA
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA
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27
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Changes in life history and population size can explain the relative neutral diversity levels on X and autosomes in extant human populations. Proc Natl Acad Sci U S A 2020; 117:20063-20069. [PMID: 32747577 DOI: 10.1073/pnas.1915664117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
In human populations, the relative levels of neutral diversity on the X and autosomes differ markedly from each other and from the naïve theoretical expectation of 3/4. Here we propose an explanation for these differences based on new theory about the effects of sex-specific life history and given pedigree-based estimates of the dependence of human mutation rates on sex and age. We demonstrate that life history effects, particularly longer generation times in males than in females, are expected to have had multiple effects on human X-to-autosome (X:A) diversity ratios, as a result of male-biased mutation rates, the equilibrium X:A ratio of effective population sizes, and the differential responses to changes in population size. We also show that the standard approach of using divergence between species to correct for male mutation bias results in biased estimates of X:A effective population size ratios. We obtain alternative estimates using pedigree-based estimates of the male mutation bias, which reveal that X:A ratios of effective population sizes are considerably greater than previously appreciated. Finally, we find that the joint effects of historical changes in life history and population size can explain the observed X:A diversity ratios in extant human populations. Our results suggest that ancestral human populations were highly polygynous, that non-African populations experienced a substantial reduction in polygyny and/or increase in the male-to-female ratio of generation times around the Out-of-Africa bottleneck, and that current diversity levels were affected by fairly recent changes in sex-specific life history.
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28
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von Rueden C. Making and unmaking egalitarianism in small-scale human societies. Curr Opin Psychol 2020; 33:167-171. [DOI: 10.1016/j.copsyc.2019.07.037] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 07/20/2019] [Indexed: 11/28/2022]
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29
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Winegard B, Kirsch A, Vonasch A, Winegard B, Geary DC. Coalitional Value Theory: an Evolutionary Approach to Understanding Culture. EVOLUTIONARY PSYCHOLOGICAL SCIENCE 2020. [DOI: 10.1007/s40806-020-00235-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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30
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Alami S, von Rueden C, Seabright E, Kraft TS, Blackwell AD, Stieglitz J, Kaplan H, Gurven M. Mother's social status is associated with child health in a horticulturalist population. Proc Biol Sci 2020; 287:20192783. [PMID: 32156217 PMCID: PMC7126073 DOI: 10.1098/rspb.2019.2783] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 02/13/2020] [Indexed: 12/27/2022] Open
Abstract
High social status is often associated with greater mating opportunities and fertility for men, but do women also obtain fitness benefits of high status? Greater resource access and child survivorship may be principal pathways through which social status increases women's fitness. Here, we examine whether peer-rankings of women's social status (indicated by political influence, project leadership, and respect) positively covaries with child nutritional status and health in a community of Amazonian horticulturalists. We find that maternal political influence is associated with improved child health outcomes in models adjusting for maternal age, parental height and weight, level of schooling, household income, family size, and number of kin in the community. Children of politically influential women have higher weight-for-age (B = 0.33; 95% CI = 0.12-0.54), height-for-age (B = 0.32; 95% CI = 0.10-0.54), and weight-for-height (B = 0.24; 95% CI = 0.04-0.44), and they are less likely to be diagnosed with common illnesses (OR = 0.48; 95% CI = 0.31-0.76). These results are consistent with women leveraging their social status to enhance reproductive success through improvements in child health. We discuss these results in light of parental investment theory and the implications for the evolution of female social status in humans.
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Affiliation(s)
- Sarah Alami
- Department of Anthropology, University of California, Santa Barbara, CA 93106, USA
| | | | - Edmond Seabright
- Department of Anthropology, University of New Mexico, Albuquerque, NM 87131, USA
| | - Thomas S. Kraft
- Department of Anthropology, University of California, Santa Barbara, CA 93106, USA
| | - Aaron D. Blackwell
- Department of Anthropology, Washington State University, Pullman, WA 99163, USA
| | | | - Hillard Kaplan
- Economic Science Institute, Chapman University, Orange, CA, USA
| | - Michael Gurven
- Department of Anthropology, University of California, Santa Barbara, CA 93106, USA
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31
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Muñoz-Reyes JA, Polo P, Valenzuela N, Pavez P, Ramírez-Herrera O, Figueroa O, Rodriguez-Sickert C, Díaz D, Pita M. The Male Warrior Hypothesis: Testosterone-related Cooperation and Aggression in the Context of Intergroup Conflict. Sci Rep 2020; 10:375. [PMID: 31942026 PMCID: PMC6962424 DOI: 10.1038/s41598-019-57259-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 12/20/2019] [Indexed: 12/28/2022] Open
Abstract
The Male Warrior Hypothesis (MWH) establishes that men's psychology has been shaped by inter-group competition to acquire and protect reproductive resources. In this context, sex-specific selective pressures would have favored cooperation with the members of one's group in combination with hostility towards outsiders. We investigate the role of developmental testosterone, as measured indirectly through static markers of prenatal testosterone (2D:4D digit ratio) and pubertal testosterone (body musculature and facial masculinity), on both cooperation and aggressive behavior in the context of intergroup conflict among men. Supporting the MWH, our results show that the intergroup conflict scenario promotes cooperation within group members and aggression toward outgroup members. Regarding the hormonal underpinnings of this phenomenon, we find that body musculature is positively associated with aggression and cooperation, but only for cooperation when context (inter-group competition) is taken into account. Finally, we did not find evidence that the formidability of the group affected individual rates of aggression or cooperation, controlling for individual characteristics.
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Affiliation(s)
- J A Muñoz-Reyes
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile.
| | - P Polo
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile
| | - N Valenzuela
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile.,Departamento de Ciencias Biológicas, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Viña del Mar, Chile
| | - P Pavez
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile
| | - O Ramírez-Herrera
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile
| | - O Figueroa
- Laboratorio de Comportamiento Animal y Humano, Centro de Estudios Avanzados, Universidad de Playa Ancha, Valparaíso, Chile.,Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - C Rodriguez-Sickert
- Centro de Investigación en Complejidad Social, Facultad de Gobierno, Universidad del Desarrollo, Santiago, Chile
| | - D Díaz
- Facultad de Ciencias Económicas, Universidad de Chile, Santiago, Chile
| | - M Pita
- Departamento de Biología, Universidad Autónoma de Madrid, Madrid, Spain
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Testing the Trivers-Willard Hypothesis on Polish kings and dukes. ANTHROPOLOGICAL REVIEW 2019. [DOI: 10.2478/anre-2019-0030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Trivers-Willard Hypothesis (TWH), frequently investigated by evolutionary psychologists, states that human beings may have evolved to produce a greater number of sons when having a high status, and a greater number of daughters when having a low status. To test this hypothesis, we examined the sex of children of Polish high status: kings, dukes, magnates families; and of low status: peasants, burghers and gentry. Our findings do not provide evidence for the Trivers-Willard Hypothesis (TWH), as there were no differences between offspring’s sex ratio among any of the investigated social classes (with the exception of magnates families). We draw our conclusions with caution, as historical data carry many limitations.
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Zhu N, Chang L. Evolved but Not Fixed: A Life History Account of Gender Roles and Gender Inequality. Front Psychol 2019; 10:1709. [PMID: 31396136 PMCID: PMC6664064 DOI: 10.3389/fpsyg.2019.01709] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Accepted: 07/09/2019] [Indexed: 12/03/2022] Open
Abstract
The rift between evolutionary psychology and the biosocial model of gender relations impedes a fuller understanding of gender roles and gender inequality. In a novel evolutionary account that complements both existing theories, we highlight life history strategies as intermediate mechanism linking distal environmental forces to variations in gender relations. Specifically, traditional versus modernized gender roles are seen as shaped by present-oriented versus future-oriented reproductive strategies, which are sensitive to uncontrollable morbidity-mortality risks. Gender inequality stems from a combination of present-oriented reproductive strategies adapted to high-risk environments and dominance hierarchies resulting from societal competition (i.e., the probability of obtaining resources desired by others through personal efforts). By contrast, gender egalitarian values develop as people increasingly enact future-oriented reproductive strategies in a competitive but orderly and controllable environment, which is conducive to prestige hierarchies. The current account provides novel interpretations of phenomena ranging from sex differences in mate preference, sociosexuality, and sexism to cross-cultural variability in marital systems and cultural practices. All of these serve to support the view that gender relations are evolved, changeable, and influenced by the interaction between ecological and social environments in ways predicted by the life history mechanism.
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Affiliation(s)
- Nan Zhu
- Department of Psychology, University of Macau, Macau, China
| | - Lei Chang
- Department of Psychology, University of Macau, Macau, China
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36
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Self-esteem as an adaptive sociometer of mating success: Evaluating evidence of sex-specific psychological design across 10 world regions. PERSONALITY AND INDIVIDUAL DIFFERENCES 2019. [DOI: 10.1016/j.paid.2019.02.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Abstract
Where should we look to understand the origin of inequality? I propose an unusual window of evidence—modern societies. I hypothesize that evidence for the origin of inequality is encoded in the institutional structure of industrial societies. To test this idea, I use a model to project modern trends into the past. This model takes the modern relation between energy, hierarchy, and inequality and creates a hindcast of the origin of inequality. The results are broadly consistent with the available evidence. The model predicts an explosion of inequality with the transition from hunter-gathering to agriculture, followed by a plateau. This finding potentially opens a new window of evidence into the origin of inequality.
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38
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Archer J. The reality and evolutionary significance of human psychological sex differences. Biol Rev Camb Philos Soc 2019; 94:1381-1415. [DOI: 10.1111/brv.12507] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 02/14/2019] [Accepted: 02/21/2019] [Indexed: 01/03/2023]
Affiliation(s)
- John Archer
- Department of PsychologyUniversity of Central Lancashire Preston Lancashire PR1 2HE U.K
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Minocher R, Duda P, Jaeggi AV. Explaining marriage patterns in a globally representative sample through socio-ecology and population history: A Bayesian phylogenetic analysis using a new supertree. EVOL HUM BEHAV 2019. [DOI: 10.1016/j.evolhumbehav.2018.11.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Investigating mitonuclear interactions in human admixed populations. Nat Ecol Evol 2019; 3:213-222. [PMID: 30643241 PMCID: PMC6925600 DOI: 10.1038/s41559-018-0766-1] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 11/22/2018] [Indexed: 12/13/2022]
Abstract
To function properly, mitochondria utilize products of 37 mitochondrial and >1,000 nuclear genes, which should be compatible with each other. Discordance between mitochondrial and nuclear genetic ancestry could contribute to phenotypic variation in admixed populations. Here, we explored potential mitonuclear incompatibility in six admixed human populations from the Americas: African Americans, African Caribbeans, Colombians, Mexicans, Peruvians and Puerto Ricans. By comparing nuclear versus mitochondrial ancestry in these populations, we first show that mitochondrial DNA (mtDNA) copy number decreases with increasing discordance between nuclear and mtDNA ancestry. The direction of this effect is consistent across mtDNA haplogroups of different geographic origins. This observation indicates suboptimal regulation of mtDNA replication when its components are encoded by nuclear and mtDNA genes with different ancestry. Second, while most populations analysed exhibit no such trend, in African Americans and Puerto Ricans, we find a significant enrichment of ancestry at nuclear-encoded mitochondrial genes towards the source populations contributing the most prevalent mtDNA haplogroups (African and Native American, respectively). This possibly reflects compensatory effects of selection in recovering mitonuclear interactions optimized in the source populations. Our results provide evidence of mitonuclear interactions in human admixed populations and we discuss their implications for human health and disease.
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When Saying "Sorry" Isn't Enough: Is Some Suicidal Behavior a Costly Signal of Apology? : A Cross-Cultural Test. HUMAN NATURE (HAWTHORNE, N.Y.) 2018; 30:117-141. [PMID: 30552579 DOI: 10.1007/s12110-018-9333-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Lethal and nonlethal suicidal behaviors are major global public health problems. Much suicidal behavior (SB) occurs after the suicide victim committed a murder or other serious transgression. The present study tested a novel evolutionary model termed the Costly Apology Model (CAM) against the ethnographic record. The bargaining model (BRM) sees nonlethal suicidal behavior as an evolved costly signal of need in the wake of adversity. Relying on this same theoretical framework, the CAM posits that nonlethal suicidal behavior can sometimes serve as an honest signal of apology in the wake of committing a severe transgression, thereby repairing valuable social relationships. To test this hypothesis, the CAM was operationalized into a set of variables, and two independent coders coded 473 text records on suicidal behavior from 53 cultures from the probability sample of the Human Relations Area Files. The results indicated that in ethnographic accounts of suicidal behavior, transgressions, punishment, and shame were relatively common, supporting the CAM, but explicit motives to apologize and evidence of forgiveness were rare, contrary to the CAM. The theoretical variables of the CAM nevertheless formed a cluster distinct from the BRM, and a subset of cases of suicidal behavior were largely related to transgressions and other CAM variables rather than BRM or other variables. Support for the CAM varied widely across cultures, but there was evidence for it in every major geographical region. Exploratory analyses suggested that the CAM is potentially more likely to occur in response to severe conflicts concerning transgressions committed against nonkin. Furthermore, in text records that involved transgressions, male suicidal behavior was most frequently associated with murder, whereas female suicidal behavior was most frequently associated with sexual transgressions. In conclusion, the results provided mixed support for the hypothesis that some instances of suicidal behavior function to send a costly signal of apology to those harmed by a transgression.
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Archer CR, Recker M, Duffy E, Hosken DJ. Intralocus sexual conflict can resolve the male-female health-survival paradox. Nat Commun 2018; 9:5048. [PMID: 30487539 PMCID: PMC6261961 DOI: 10.1038/s41467-018-07541-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 11/08/2018] [Indexed: 11/09/2022] Open
Abstract
At any given age, men are more likely to die than women, but women have poorer health at older ages. This is referred to as the “male-female, health-survival paradox”, which is not fully understood. Here, we provide a general solution to the paradox that relies on intralocus sexual conflict, where alleles segregating in the population have late-acting positive effects on male fitness, but negative effects on female health. Using an evolutionary modelling framework, we show that male-benefit, female-detriment alleles can spread if they are expressed after female reproduction stops. We provide support for our conflict based solution using experimental Drosophila data. Our results show that selecting for increased late-life male reproductive effort can increase male fitness but have a detrimental effect on female fitness. Furthermore, we show that late-life male fertility is negatively genetically correlated with female health. Our study suggests that intralocus sexual conflict could resolve the health-survival paradox. Although men have lower survival across ages, women have poorer health than men as they age. Here, Archer et al. suggest that this pattern is explained by intralocus sexual conflict and provide supporting evidence from a mathematical model and experiments with Drosophila.
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Affiliation(s)
- C Ruth Archer
- Science and Engineering Research Support Facility, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK
| | - Mario Recker
- Science and Engineering Research Support Facility, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK.,College of Engineering, Mathematics and Physical Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK
| | - Eoin Duffy
- Science and Engineering Research Support Facility, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK
| | - David J Hosken
- Science and Engineering Research Support Facility, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK.
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von Rueden C, Alami S, Kaplan H, Gurven M. Sex differences in political leadership in an egalitarian society. EVOL HUM BEHAV 2018; 39:402-411. [PMID: 30319239 PMCID: PMC6178229 DOI: 10.1016/j.evolhumbehav.2018.03.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
We test the contribution of sex differences in physical formidability, education, and cooperation to the acquisition of political leadership in a small-scale society. Among forager-farmers from the Bolivian Amazon, we find that men are more likely to exercise different forms of political leadership, including verbal influence during community meetings, coordination of community projects, and dispute resolution. We show that these differences in leadership are not due to gender per se but are associated with men's greater number of cooperation partners, greater access to schooling, and greater body size and physical strength. Men's advantage in cooperation partner number is tied to their participation in larger groups and to the opportunity costs of women's intrahousehold labor. We argue these results highlight the mutual influence of sexual selection and the sexual division of labor in shaping how women and men acquire leadership.
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Affiliation(s)
- Chris von Rueden
- Jepson School of Leadership Studies, University of Richmond, 28 Westhampton Way, Richmond, VA 23173, USA
| | - Sarah Alami
- Department of Anthropology, University of California, Santa Barbara, CA 93106, USA
| | - Hillard Kaplan
- Department of Anthropology, University of New Mexico, Albuquerque, NM 87131 USA
| | - Michael Gurven
- Department of Anthropology, University of California, Santa Barbara, CA 93106, USA
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46
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Zeng TC, Aw AJ, Feldman MW. Cultural hitchhiking and competition between patrilineal kin groups explain the post-Neolithic Y-chromosome bottleneck. Nat Commun 2018; 9:2077. [PMID: 29802241 PMCID: PMC5970157 DOI: 10.1038/s41467-018-04375-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 04/24/2018] [Indexed: 01/18/2023] Open
Abstract
In human populations, changes in genetic variation are driven not only by genetic processes, but can also arise from cultural or social changes. An abrupt population bottleneck specific to human males has been inferred across several Old World (Africa, Europe, Asia) populations 5000–7000 BP. Here, bringing together anthropological theory, recent population genomic studies and mathematical models, we propose a sociocultural hypothesis, involving the formation of patrilineal kin groups and intergroup competition among these groups. Our analysis shows that this sociocultural hypothesis can explain the inference of a population bottleneck. We also show that our hypothesis is consistent with current findings from the archaeogenetics of Old World Eurasia, and is important for conceptions of cultural and social evolution in prehistory. A population bottleneck 5000-7000 years ago in human males, but not females, has been inferred across several African, European and Asian populations. Here, Zeng and colleagues synthesize theory and data to suggest that competition among patrilineal kin groups produced the bottleneck pattern.
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Affiliation(s)
- Tian Chen Zeng
- Department of Sociology, Stanford University, Stanford, CA, 94305, USA.,Mathematical and Computational Science Program, Stanford University, Stanford, CA, 94305, USA
| | - Alan J Aw
- Mathematical and Computational Science Program, Stanford University, Stanford, CA, 94305, USA.,Department of Biology, Stanford University, Stanford, CA, USA
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Abstract
Fitness is always relative to the fitness of others in the group or breeding population. Even in very low-fertility societies, individual fitness as measured by the share of genes in subsequent generations may still be maximized. Further, sexual selection theory from evolutionary biology suggests that the relationship between status and fertility will differ for males and females. For this reason it is important to examine the relationship between status and fertility separately for males and females-something few demographic studies of fertility do. When male fertility is measured separately, high-status men (as measured by their wealth and personal income) have higher fertility than low-status men, even in very low-fertility societies, so individual males appear to be maximizing their fitness within the constraints posed by a modern society. Thus male fertility cannot be considered maladaptive. When female fertility is measured separately, in both very high- and very low-fertility societies, there is not much variance across women of different statuses in completed fertility. Only in societies currently changing rapidly (with falling fertility rates) is somewhat high variance across women of different statuses in completed fertility found. What is seen across all phases of the demographic transition appears to be a continuation of two somewhat different evolved human reproductive strategies-one male, one female-in changing social and material contexts. Whether contemporary female fertility is maladaptive remains an open question.
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49
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Choleris E, Galea LAM, Sohrabji F, Frick KM. Sex differences in the brain: Implications for behavioral and biomedical research. Neurosci Biobehav Rev 2018; 85:126-145. [PMID: 29287628 PMCID: PMC5751942 DOI: 10.1016/j.neubiorev.2017.07.005] [Citation(s) in RCA: 137] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 07/16/2017] [Indexed: 01/11/2023]
Abstract
Biological differences between males and females are found at multiple levels. However, females have too often been under-represented in behavioral neuroscience research, which has stymied the study of potential sex differences in neurobiology and behavior. This review focuses on the study of sex differences in the neurobiology of social behavior, memory, emotions, and recovery from brain injury, with particular emphasis on the role of estrogens in regulating forebrain function. This work, presented by the authors at the 2016 meeting of the International Behavioral Neuroscience Society, emphasizes varying approaches from several mammalian species in which sex differences have not only been documented, but also become the focus of efforts to understand the mechanistic basis underlying them. This information may provide readers with useful experimental tools to successfully address recently introduced regulations by granting agencies that either require (e.g. the National Institutes of Health in the United States and the Canadian Institutes of Health Research in Canada) or recommend (e.g. Horizon 2020 in Europe) the inclusion of both sexes in biomedical research.
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Affiliation(s)
- Elena Choleris
- Department of Psychology and Neuroscience Program, University of Guelph, MacKinnon Bldg. Room 4020, Guelph, ON N1G 2W1, Canada.
| | - Liisa A M Galea
- Department of Psychology, Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, BC V6T1Z3, Canada
| | - Farida Sohrabji
- Women's Health in Neuroscience Program, Department of Neuroscience and Experimental Therapeutics, Texas A&M HSC College of Medicine, Bryan, TX 77807, United States
| | - Karyn M Frick
- Department of Psychology, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, United States
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50
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A model for warfare in stratified small-scale societies: The effect of within-group inequality. PLoS One 2017; 12:e0188970. [PMID: 29228014 PMCID: PMC5724843 DOI: 10.1371/journal.pone.0188970] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2017] [Accepted: 11/16/2017] [Indexed: 11/19/2022] Open
Abstract
In order to predict the features of non-raiding human warfare in small-scale, socially stratified societies, we study a coalitionary model of war that assumes that individuals participate voluntarily because their decisions serve to maximize fitness. Individual males join the coalition if war results in a net economic and thus fitness benefit. Within the model, viable offensive war ensues if the attacking coalition of males can overpower the defending coalition. We assume that the two groups will eventually fuse after a victory, with ranks arranged according to the fighting abilities of all males and that the new group will adopt the winning group’s skew in fitness payoffs. We ask whether asymmetries in skew, group size and the amount of resources controlled by a group affect the likelihood of successful war. The model shows, other things being equal, that (i) egalitarian groups are more likely to defeat their more despotic enemies, even when these are stronger, (ii) defection to enemy groups will be rare, unless the attacked group is far more despotic than the attacking one, and (iii) genocidal war is likely under a variety of conditions, in particular when the group under attack is more egalitarian. This simple optimality model accords with several empirically observed correlations in human warfare. Its success underlines the important role of egalitarianism in warfare.
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