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Kauppi JJ, Chapman SN, Pettay JE, Lahdenperä M, Lummaa V, Loehr J. Sex, age, and family structure influence dispersal behaviour after a forced migration. EVOLUTIONARY HUMAN SCIENCES 2023; 5:e21. [PMID: 37587948 PMCID: PMC10426002 DOI: 10.1017/ehs.2023.16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2023] Open
Abstract
Dispersal does not only mean moving from one environment to another, but can also refer to shifting from one social group to another. Individual characteristics such as sex, age and family structure might influence an individual's propensity to disperse. In this study, we use a unique dataset of an evacuated World War II Finnish population, to test how sex, age, number of siblings and birth order influence an individual's dispersal away from their own social group at a time when society was rapidly changing. We found that young women dispersed more than young men, but the difference decreased with age. This suggests that young men might benefit more from staying near a familiar social group, whereas young women could benefit more from moving elsewhere to find work or spouses. We also found that having more younger brothers increased the propensity for firstborns to disperse more than for laterborns, indicating that younger brothers might pressure firstborn individuals into leaving. However, sisters did not have the same effect as brothers. Overall, the results show that individual characteristics are important in understanding dispersal behaviour, but environmental properties such as social structure and the period of flux after World War II might upend the standard predictions concerning residence and dispersal. Social media summary: Individual characteristics influence dispersal away from social group after a forced migration in a Finnish population.
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Affiliation(s)
- Jenni J. Kauppi
- Department of Biology, University of Turku, 20014Turku, Finland
| | - Simon N. Chapman
- INVEST Flagship Research Centre, University of Turku, 20014Turku, Finland
| | - Jenni E. Pettay
- INVEST Flagship Research Centre, University of Turku, 20014Turku, Finland
| | | | - Virpi Lummaa
- Department of Biology, University of Turku, 20014Turku, Finland
| | - John Loehr
- University of Helsinki, 00014Helsinki, Finland
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Nitsch A, Faurie C, Lummaa V. Sibling competition, dispersal and fitness outcomes in humans. Sci Rep 2023; 13:7539. [PMID: 37160936 PMCID: PMC10169773 DOI: 10.1038/s41598-023-33700-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 04/18/2023] [Indexed: 05/11/2023] Open
Abstract
Determining how sibling interactions alter the fitness outcomes of dispersal is pivotal for the understanding of family living, but such studies are currently scarce. Using a large demographic dataset on pre-industrial humans from Finland, we studied dispersal consequences on different indicators of lifetime reproductive success according to sex-specific birth rank (a strong determinant of dispersal in our population). Contrary to the predictions of the leading hypotheses, we found no support for differential fitness benefits of dispersal for either males or females undergoing low vs. high sibling competition. Our results are inconsistent with both hypotheses that family members could have different fitness maximizing strategies depending on birth rank, and that dispersal could be mainly driven by indirect fitness benefits for philopatric family members. Our study stresses the need for studying the relative outcomes of dispersal at the family level in order to understand the evolution of family living and dispersal behaviour.
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Affiliation(s)
- Aïda Nitsch
- Department of Biology, University of Turku, Turku, Finland.
- Institute for Advanced Study in Toulouse, Université Toulouse 1 Capitole 1, Esplanade de l'Université, 31080, Cedex 6, Toulouse, France.
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
- University of Montpellier, Montpellier, France.
- Institute of Evolutionary Sciences, Centre National de la Recherche Scientifique, Place Eugène Bataillon, CC 065, 34095, Montpellier Cedex 5, France.
| | - Charlotte Faurie
- University of Montpellier, Montpellier, France
- Institute of Evolutionary Sciences, Centre National de la Recherche Scientifique, Place Eugène Bataillon, CC 065, 34095, Montpellier Cedex 5, France
| | - Virpi Lummaa
- Department of Biology, University of Turku, Turku, Finland
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3
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Templon AR, Kirsch DR, Towner MC. Contributions of evolutionary anthropology to understanding climate-induced human migration. Am J Hum Biol 2021; 33:e23635. [PMID: 34212453 PMCID: PMC8365686 DOI: 10.1002/ajhb.23635] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 06/18/2021] [Accepted: 06/19/2021] [Indexed: 12/17/2022] Open
Abstract
Humans are able to thrive in a multitude of ecological and social environments, including varied environments over an individual lifetime. Migration-leaving one place of residence for another-is a central feature of many people's life histories, and environmental change goes hand-in-hand with migration, both in terms of cause and consequence. Climate change has amplified this connection between environment and migration, with the potential to profoundly impact millions of lives. Although climate-induced migration has been at the forefront of other disciplines in the social sciences, evolutionary anthropologists (EAs) have given it little attention. In this paper we draw upon existing literature and contribute our EA perspective to present a framework for analyzing climate-induced migration that utilizes theoretical approaches from a variety of social science disciplines. We focus on three overlapping dimensions-time, space, and severity-relevant to understanding the impact of climate change on human migration. We apply this framework to case studies from North America of people impacted by climate change and extreme weather events, including hurricanes, droughts, rising sea-levels, and wildfires. We also consider how access to both economic and social resources influence decisions regarding migration. Research focused on climate-induced human migration can benefit equally from the addition of EA perspectives and a more interdisciplinary theoretical approach.
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Affiliation(s)
- Alannah R. Templon
- Department of Integrative BiologyOklahoma State UniversityStillwaterOklahomaUSA
| | - Danielle R. Kirsch
- Department of Integrative BiologyOklahoma State UniversityStillwaterOklahomaUSA
| | - Mary C. Towner
- Department of Integrative BiologyOklahoma State UniversityStillwaterOklahomaUSA
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4
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Clech L, Jones JH, Gibson M. Inequality in the household and rural-urban migration in Ethiopian farmers. EVOLUTIONARY HUMAN SCIENCES 2020; 2:e9. [PMID: 37588363 PMCID: PMC10427449 DOI: 10.1017/ehs.2020.10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Parental investment theory predicts that biases in investment favour migration by driving some of the sibling group to disperse for resources. Here we test hypotheses arising from this theory to explain patterns of rural-urban migration in south-central Ethiopia considering familial and individual strategies. We focus on the migration of low-skilled men, predicting two scenarios based on a low level of resource availability. Firstly, last-born sons will be more likely to migrate in order to offset their intra-household disadvantage when resources are limited (sibling competition). Alternatively, in households facing livelihood insecurity, older sons will migrate in order to free resources for their younger dependant brothers (reflecting sibling cooperation). Demographic, economic and relational data were collected from 217 families of male migrants, including information for 830 male adults. We performed multivariate analyses, including Bayesian generalised linear models and mixed models, to analyse quantitative data with a focus on household and individual likelihood of out-migration. Consistent with the predictions from parental investment theory, migration is dependent on intra-household resource allocation. Depending on the stage of the family cycle and livelihood context, families and individuals present different strategies: labour migration may result from sibling competition or from cooperation for resource enhancement.
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Affiliation(s)
- Lucie Clech
- Department of Anthropology and Archaeology, University of Bristol, 43 Woodland Rd, BristolBS81TH, UK
- Department of Anthropology, Stanford University, 50, 450 Serra Mall, Stanford, CA94305, USA
| | - James Holland Jones
- Department of Earth System Science, Stanford University, 473 Via Ortega, Stanford, CA94305USA
| | - Mhairi Gibson
- Department of Anthropology and Archaeology, University of Bristol, 43 Woodland Rd, BristolBS81TH, UK
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Clech L, Hazel A, Gibson MA. Does Kin-Selection Theory Help to Explain Support Networks among Farmers in South-Central Ethiopia? HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE 2019; 30:422-447. [PMID: 31729694 DOI: 10.1007/s12110-019-09352-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Social support networks play a key role in human livelihood security, especially in vulnerable communities. Here we explore how evolutionary ideas of kin selection and intrahousehold resource competition can explain individual variation in daily support network size and composition in a south-central Ethiopian agricultural community. We consider both domestic and agricultural help across two generations with different wealth-transfer norms that yield different contexts for sibling competition. For farmers who inherited land rights from family, firstborns were more likely to report daily support from parents and to have larger nonparental kin networks (n = 180). Compared with other farmers, firstborns were also more likely to reciprocate their parents' support, and to help nonparental kin without reciprocity. For farmers who received land rights from the government (n = 151), middle-born farmers reported more nonparental kin in their support networks compared with other farmers; nonreciprocal interactions were particularly common in both directions. This suggests a diversification of adult support networks to nonparental kin, possibly in response to a long-term parental investment disadvantage of being middle-born sons. In all instances, regardless of inheritance, lastborn farmers were the most disadvantaged in terms of kin support. Overall, we found that nonreciprocal interactions among farmers followed kin selection predictions. Direct reciprocity explained a substantial part of the support received from kin, suggesting the importance of the combined effects of kin selection and reciprocity for investment from kin.
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Affiliation(s)
- Lucie Clech
- Department of Anthropology and Archaeology, University of Bristol, 43 Woodland Rd, Bristol, BS81TH, UK. .,Department of Anthropology, Stanford University, 50, 450 Serra Mall, Stanford, CA, 94305, USA.
| | - Ashley Hazel
- Department of Earth System Science, Stanford University, 473 Via Ortega, Stanford, CA, 94305, USA
| | - Mhairi A Gibson
- Department of Anthropology and Archaeology, University of Bristol, 43 Woodland Rd, Bristol, BS81TH, UK
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6
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Koster J, Lukas D, Nolin D, Power E, Alvergne A, Mace R, Ross CT, Kramer K, Greaves R, Caudell M, MacFarlan S, Schniter E, Quinlan R, Mattison S, Reynolds A, Yi-Sum C, Massengill E. Kinship ties across the lifespan in human communities. Philos Trans R Soc Lond B Biol Sci 2019; 374:20180069. [PMID: 31303163 DOI: 10.1098/rstb.2018.0069] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A hypothesis for the evolution of long post-reproductive lifespans in the human lineage involves asymmetries in relatedness between young immigrant females and the older females in their new groups. In these circumstances, inter-generational reproductive conflicts between younger and older females are predicted to resolve in favour of the younger females, who realize fewer inclusive fitness benefits from ceding reproduction to others. This conceptual model anticipates that immigrants to a community initially have few kin ties to others in the group, gradually showing greater relatedness to group members as they have descendants who remain with them in the group. We examine this prediction in a cross-cultural sample of communities, which vary in their sex-biased dispersal patterns and other aspects of social organization. Drawing on genealogical and demographic data, the analysis provides general but not comprehensive support for the prediction that average relatedness of immigrants to other group members increases as they age. In rare cases, natal members of the community also exhibit age-related increases in relatedness. We also find large variation in the proportion of female group members who are immigrants, beyond simple traditional considerations of patrilocality or matrilocality, which raises questions about the circumstances under which this hypothesis of female competition are met. We consider possible explanations for these heterogenous results, and we address methodological considerations that merit increased attention for research on kinship and reproductive conflict in human societies. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.
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Affiliation(s)
- Jeremy Koster
- 1 Department of Anthropology, University of Cincinnati , Cincinnati, OH 45221-0380 , USA.,2 Department of Human Behavior, Ecology, and Culture, Max Planck Institute of Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany
| | - Dieter Lukas
- 2 Department of Human Behavior, Ecology, and Culture, Max Planck Institute of Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany
| | - David Nolin
- 3 Department of Anthropology and Population Research Institute, Penn State University , University Park, PA 16802 , USA
| | - Eleanor Power
- 4 Department of Methodology, The London School of Economics and Political Science , Houghton Street, London WC2A 2AE , UK
| | - Alexandra Alvergne
- 5 School of Anthropology and Museum Ethnography, University of Oxford , 51 Banbury Road, Oxford OX2 6PE , UK
| | - Ruth Mace
- 6 Department of Anthropology, University College London , 14 Taviton St, London WC1H 0BW , UK.,7 School of Life Sciences, Lanzhou University , 222 Tianshui NanLu, Lanzhou, Gansu 73000 , People's Republic of China
| | - Cody T Ross
- 2 Department of Human Behavior, Ecology, and Culture, Max Planck Institute of Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany
| | - Karen Kramer
- 8 Department of Anthropology, University of Utah , Salt Lake City, UT 84112 , USA
| | - Russell Greaves
- 8 Department of Anthropology, University of Utah , Salt Lake City, UT 84112 , USA
| | - Mark Caudell
- 9 Paul G. Allen School for Global Animal Health, Washington State University , Pullman, WA 99164 , USA
| | - Shane MacFarlan
- 8 Department of Anthropology, University of Utah , Salt Lake City, UT 84112 , USA
| | - Eric Schniter
- 10 Economic Sciences Institute, Chapman University , Orange, CA 92866 , USA
| | - Robert Quinlan
- 11 Department of Anthropology, Washington State University , Pullman, WA 99164 , USA
| | - Siobhan Mattison
- 12 Department of Anthropology, University of New Mexico , Albuquerque, NM 87131 , USA
| | - Adam Reynolds
- 12 Department of Anthropology, University of New Mexico , Albuquerque, NM 87131 , USA
| | - Chun Yi-Sum
- 12 Department of Anthropology, University of New Mexico , Albuquerque, NM 87131 , USA.,13 Harvard-Yenching Institute , Vanserg Hall, Suite 20, 25 Francis Avenue, Cambridge, MA 02138 , USA
| | - Eric Massengill
- 12 Department of Anthropology, University of New Mexico , Albuquerque, NM 87131 , USA
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Borgerhoff Mulder M, Towner MC, Baldini R, Beheim BA, Bowles S, Colleran H, Gurven M, Kramer KL, Mattison SM, Nolin DA, Scelza BA, Schniter E, Sear R, Shenk MK, Voland E, Ziker J. Differences between sons and daughters in the intergenerational transmission of wealth. Philos Trans R Soc Lond B Biol Sci 2019; 374:20180076. [PMID: 31303159 DOI: 10.1098/rstb.2018.0076] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Persistent interest lies in gender inequality, especially with regard to the favouring of sons over daughters. Economists are concerned with how privilege is transmitted across generations, and anthropologists have long studied sex-biased inheritance norms. There has, however, been no focused cross-cultural investigation of how parent-offspring correlations in wealth vary by offspring sex. We estimate these correlations for 38 wealth measures, including somatic and relational wealth, from 15 populations ranging from hunter-gatherers to small-scale farmers. Although small sample sizes limit our statistical power, we find no evidence of ubiquitous male bias, at least as inferred from comparing parent-son and parent-daughter correlations. Rather we find wide variation in signatures of sex bias, with evidence of both son and daughter-biased transmission. Further, we introduce a model that helps pinpoint the conditions under which simple mid-point parent-offspring wealth correlations can reveal information about sex-biased parental investment. Our findings are relevant to the study of female-biased kinship by revealing just how little normative descriptors of kinship systems, such as patrilineal inheritance, capture intergenerational correlations in wealth, and how variable parent-son and parent-daughter correlations can be. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.
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Affiliation(s)
| | - Mary C Towner
- 3 Department of Integrative Biology, Oklahoma State University Stillwater , Stillwater, OK , USA
| | - Ryan Baldini
- 2 Graduate Group in Ecology, University of California Davis , Davis, CA , USA
| | - Bret A Beheim
- 4 Department of Human Behavior, Ecology, and Culture, Max Planck Institute for Evolutionary Anthropology , Leipzig, Sachsen , Germany
| | | | - Heidi Colleran
- 6 Department of Linguistic and Cultural Evolution, Max Planck Institute for the Science of Human History , Jena, Thüringen , Germany
| | - Michael Gurven
- 7 Department of Anthropology, University of California Santa Barbara , Santa Barbara, CA , USA
| | - Karen L Kramer
- 8 Department of Anthropology, University of Utah , Salt Lake City, UT , USA
| | - Siobhán M Mattison
- 9 Department of Anthropology, University of New Mexico , Albuquerque, NM , USA
| | - David A Nolin
- 10 Department of Anthropology, Pennsylvania State University , University Park, PA , USA
| | - Brooke A Scelza
- 11 Department of Anthropology, University of California Los Angeles , Los Angeles, CA , USA
| | - Eric Schniter
- 12 Economic Science Institute Chapman University , CA 92866
| | - Rebecca Sear
- 13 Department of Population Health, London School of Hygiene and Tropical Medicine , London , UK
| | - Mary K Shenk
- 10 Department of Anthropology, Pennsylvania State University , University Park, PA , USA
| | - Eckart Voland
- 14 Institut fur Philosophie, Justus Liebig Universitat Giessen , Giessen, Hessen , Germany
| | - John Ziker
- 15 Department of Anthropology, Boise State University , Boise, ID , USA
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Koster J. Family ties: the multilevel effects of households and kinship on the networks of individuals. ROYAL SOCIETY OPEN SCIENCE 2018; 5:172159. [PMID: 29765670 PMCID: PMC5936935 DOI: 10.1098/rsos.172159] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2017] [Accepted: 03/13/2018] [Indexed: 06/08/2023]
Abstract
Among social mammals, humans uniquely organize themselves into communities of households that are centred around enduring, predominantly monogamous unions of men and women. As a consequence of this social organization, individuals maintain social relationships both within and across households, and potentially there is conflict among household members about which social ties to prioritize or de-emphasize. Extending the logic of structural balance theory, I predict that there will be considerable overlap in the social networks of individual household members, resulting in a pattern of group-level reciprocity. To test this prediction, I advance the Group-Structured Social Relations Model, a generalized linear mixed model that tests for group-level effects in the inter-household social networks of individuals. The empirical data stem from social support interviews conducted in a community of indigenous Nicaraguan horticulturalists, and model results show high group-level reciprocity among households. Although support networks are organized around kinship, covariates that test predictions of kin selection models do not receive strong support, potentially because most kin-directed altruism occurs within households, not between households. In addition, the models show that households with high genetic relatedness in part from children born to adulterous relationships are less likely to assist each other.
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Nitsch A, Lummaa V, Faurie C. Sibship effects on dispersal behaviour in a pre-industrial human population. J Evol Biol 2016; 29:1986-1998. [DOI: 10.1111/jeb.12922] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 06/14/2016] [Accepted: 06/15/2016] [Indexed: 11/30/2022]
Affiliation(s)
- A. Nitsch
- Department of Animal and Plant Sciences; University of Sheffield; Sheffield UK
- Institute for Advanced Study in Toulouse; Toulouse France
- University of Montpellier; Montpellier France
- Institute des Sciences de l'Evolution-Montpellier; Centre National de la Recherche Scientifique; Montpellier Cedex 5 France
| | - V. Lummaa
- Department of Biology; University of Turku; Turku Finland
| | - C. Faurie
- University of Montpellier; Montpellier France
- Institute des Sciences de l'Evolution-Montpellier; Centre National de la Recherche Scientifique; Montpellier Cedex 5 France
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Abstract
Formal models of life-history evolution have been used to illuminate both the peculiarities of the human life cycle and its commonalities with those of other taxa. Understanding reproductive decisions in both the contemporary market-based economies of wealthy nation-states and rapidly changing populations largely of the Global South presents particular challenges to evolutionary life-history theory for several reasons. These include (a) the rapidity with which reproductive patterns change, (b) the magnitude of fertility reduction from previous equilibria, and (c) the frequent absence or even reversal of expected wealth-fertility gradients. These empirical challenges have been met to an increasing extent by specifically incorporating durable wealth and resource transfers into more traditional life-history models. Such relatively new models build on classical life-history theory to generate novel predictions. Among these are quite robust predictions that the existence of heritable wealth will decrease optimal fertility and that, once the system of resource transfers is established, fertility and resource transfers will coevolve.
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Affiliation(s)
- James Holland Jones
- Department of Anthropology, and
- Woods Institute for the Environment, Stanford University, Stanford, California 94305
- Division of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
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11
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Gibson MA, Gurmu E. Rural to urban migration is an unforeseen impact of development intervention in Ethiopia. PLoS One 2012; 7:e48708. [PMID: 23155400 PMCID: PMC3498254 DOI: 10.1371/journal.pone.0048708] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 10/02/2012] [Indexed: 11/18/2022] Open
Abstract
Rural development initiatives across the developing world are designed to improve community well-being and livelihoods. However they may also have unforeseen consequences, in some cases placing further demands on stretched public services. In this paper we use data from a longitudinal study of five Ethiopian villages to investigate the impact of a recent rural development initiative, installing village-level water taps, on rural to urban migration of young adults. Our previous research has identified that tap stands dramatically reduced child mortality, but were also associated with increased fertility. We demonstrate that the installation of taps is associated with increased rural-urban migration of young adults (15-30 years) over a 15 year period (15.5% migrate out, n = 1912 from 1280 rural households). Young adults with access to this rural development intervention had three times the relative risk of migrating to urban centres compared to those without the development. We also identify that family dynamics, specifically sibling competition for limited household resources (e.g. food, heritable land and marriage opportunities), are key to understanding the timing of out-migration. Birth of a younger sibling doubled the odds of out-migration and starting married life reduced it. Rural out-migration appears to be a response to increasing rural resource scarcity, principally competition for agricultural land. Strategies for livelihood diversification include education and off-farm casual wage-labour. However, jobs and services are limited in urban centres, few migrants send large cash remittances back to their families, and most return to their villages within one year without advanced qualifications. One benefit for returning migrants may be through enhanced social prestige and mate-acquisition on return to rural areas. These findings have wide implications for current understanding of the processes which initiate rural-to-urban migration and transitions to low fertility, as well as for the design and implementation of development intervention across the rural and urban developing world.
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Affiliation(s)
- Mhairi A Gibson
- Department of Archaeology and Anthropology, University of Bristol, Bristol, United Kingdom.
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12
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Beise J, Voland E. Intrafamilial resource competition and mate competition shaped social-group-specific natal dispersal in the 18th and 19th century Krummhörn population. Am J Hum Biol 2008; 20:325-36. [DOI: 10.1002/ajhb.20730] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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13
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Dickinson JL, McGowan A. Winter resource wealth drives delayed dispersal and family-group living in western bluebirds. Proc Biol Sci 2005; 272:2423-8. [PMID: 16243691 PMCID: PMC1559973 DOI: 10.1098/rspb.2005.3269] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Delayed dispersal, where offspring remain with parents beyond the usual period of dependence, is the typical route leading to formation of kin-based cooperative societies. The prevailing explanations for why offspring stay home are variation in resource wealth, in which offspring of wealthy parents benefit disproportionately by staying home, and nepotism, where the tendency for parents to be less aggressive and share food with offspring makes home a superior place to wait to breed. These hypotheses are not strict alternatives, as only wealthy parents have sufficient resources to share. In western bluebirds, Sialia mexicana, sons usually delay dispersal until after winter, gaining feeding advantages through maternal nepotism in a familial winter group. Experimentally reducing resource wealth (mistletoe) by half on winter territories caused sons to disperse in summer, even though their parents remained on the territory during the winter. Only 8% of sons remained with their parents on mistletoe-removal territories compared to 50% of sons on control territories (t(9,10)=3.33, p<0.005). This study is the first to demonstrate that experimentally reducing wealth of a natural food resource reduces delayed dispersal, facilitating nepotism and family-group living. The results clarify the roles of year-round residency, resource limitation and relative wealth outside the breeding season in facilitating the formation of kin-based cooperative societies.
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Affiliation(s)
- Janis L Dickinson
- University of California, Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, Berkeley, CA 94720-3160, USA.
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14
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