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Brandl E, Emmott EH, Mace R. Adoption, Fostering, and Parental Absence in Vanuatu. HUMAN NATURE (HAWTHORNE, N.Y.) 2023; 34:422-455. [PMID: 37642860 PMCID: PMC10543845 DOI: 10.1007/s12110-023-09456-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 07/28/2023] [Indexed: 08/31/2023]
Abstract
Alloparenting, wherein people provide care to children who are not their biological offspring, is a key aspect of human child-rearing. In the Pacific, many children are adopted or fostered by custodial alloparents even when both biological parents are still alive. From a behavioral ecology perspective, such behaviors are puzzling: why parent someone else's child at your expense? Furthermore, little is known about how these arrangements are made in Pacific Islander societies today, who provides care, and what kinds of outcomes fostered children experience. A better understanding of these proximate factors may help reveal the ultimate drivers behind custodial alloparenting. Here, we report findings from a survey carried out with the caregivers of 282 children in rural areas of Vanuatu, an island nation in Melanesia. Most fostered and adopted children lived with relatives such as aunts, uncles, and grandparents (87.5%) rather than unrelated caregivers, with a strong preference for maternal kin. The most common reasons for these arrangements were that the parents had separated (16.7%), were engaging in labor migration (27.1%), or a combination of both (27.1%). Results for investment in children's education and their educational outcomes were mixed, although children removed from crisis situations did more poorly than children removed for aspirational reasons. Our findings suggest that custodial alloparenting helps families adapt to socioeconomic transitions and changing marriage practices. Outcomes may depend on a range of factors, such as the reason children were transferred out of the natal home to begin with.
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Affiliation(s)
- Eva Brandl
- Lise Meitner Research Group BirthRites, Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, 04103, Leipzig, Germany.
| | - Emily H Emmott
- Department of Anthropology, University College London, London, WC1E 6BT, UK
| | - Ruth Mace
- Department of Anthropology, University College London, London, WC1E 6BT, UK
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Pettay JE, Danielsbacka M, Helle S, Perry G, Daly M, Tanskanen AO. Parental Investment by Birth Fathers and Stepfathers : Roles of Mating Effort and Childhood Co-residence Duration. HUMAN NATURE (HAWTHORNE, N.Y.) 2023:10.1007/s12110-023-09450-6. [PMID: 37300791 DOI: 10.1007/s12110-023-09450-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/17/2023] [Indexed: 06/12/2023]
Abstract
This study investigates the determinants of paternal investment by birth fathers and stepfathers. Inclusive fitness theory predicts higher parental investment in birth children than stepchildren, and this has consistently been found in previous studies. Here we investigate whether paternal investment varies with childhood co-residence duration and differs between stepfathers and divorced birth fathers by comparing the investment of (1) stepfathers, (2) birth fathers who are separated from the child's mother, and (3) birth fathers who still are in a relationship with her. Path analysis was conducted using cross-sectional data from adolescents and younger adults (aged 17-19, 27-29, and 37-39 years) from the German Family Panel (pairfam), collected in 2010-2011 (n = 8326). As proxies of paternal investment, we used financial and practical help, emotional support, intimacy, and emotional closeness, as reported by the children. We found that birth fathers who were still in a relationship with the mother invested the most, and stepfathers invested the least. Furthermore, the investment of both separated fathers and stepfathers increased with the duration of co-residence with the child. However, in the case of financial help and intimacy, the effect of childhood co-residence duration was stronger in stepfathers than in separated fathers. Our findings support inclusive fitness theory and mating effort theory in explaining social behavior and family dynamics in this population. Furthermore, social environment, such as childhood co-residence was associated with paternal investment.
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Affiliation(s)
- Jenni E Pettay
- Department of Social Research, University of Turku, Assistentinkatu 7, 20014, Turku, Finland.
| | - Mirkka Danielsbacka
- Department of Social Research, University of Turku, Assistentinkatu 7, 20014, Turku, Finland
- Population Research Institute, Helsinki, Finland
| | - Samuli Helle
- Department of Social Research, University of Turku, Assistentinkatu 7, 20014, Turku, Finland
| | - Gretchen Perry
- Department of Sociology, Anthropology & Human Services, University of Canterbury, Christchurch, New Zealand
| | - Martin Daly
- Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, ON, Canada
| | - Antti O Tanskanen
- Department of Social Research, University of Turku, Assistentinkatu 7, 20014, Turku, Finland
- Population Research Institute, Helsinki, Finland
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Daly M, Perry G. Sexual Selection and the Treatment of Predecessors' Progeny by Replacement Mates. Front Psychol 2022; 13:924238. [PMID: 35769745 PMCID: PMC9234565 DOI: 10.3389/fpsyg.2022.924238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 05/24/2022] [Indexed: 11/23/2022] Open
Abstract
Darwin's theory of sexual selection provides a useful framework for understanding the behavior of stepparents. A non-human animal whose new mate has dependent young may kill, ignore, or adopt the predecessor's progeny. The third option has been interpreted as courtship ("mating effort"), and whether selection favors such investment over killing or ignoring the young apparently depends on aspects of the species-typical ecology and demography. The tripartite categorization of responses is a simplification, however, There is variability both within and between species along a continuum from rejection to "full adoption." The average stepparent invests less than the average birth parent, but more than nothing. Human stepparents have often been found to kill young children at higher rates than birth parents, but stepparental infanticide cannot plausibly be interpreted as a human adaptation, both because it is extremely rare and because it is almost certainly more likely to reduce the killer's fitness than to raise it. How sexual selection theory remains relevant to human stepparenting is by suggesting testable hypotheses about predictors of the variability in stepparental investment.
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Affiliation(s)
- Martin Daly
- Department of Psychology, Neuroscience & Behavior, McMaster University, Hamilton, ON, Canada
| | - Gretchen Perry
- Department of Sociology, Anthropology & Human Services, University of Canterbury, Christchurch, New Zealand
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Schacht R, Meeks H, Fraser A, Smith KR. Was Cinderella just a fairy tale? Survival differences between stepchildren and their half-siblings. Philos Trans R Soc Lond B Biol Sci 2021; 376:20200032. [PMID: 33938278 PMCID: PMC8090814 DOI: 10.1098/rstb.2020.0032] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/24/2020] [Indexed: 11/12/2022] Open
Abstract
The death of a parent, particularly the mother, is linked to a suite of negative outcomes across the life-course. Compounding concerns for child outcomes are expectations of poor treatment by step-parents after parental remarriage. Indeed, folk tales of step-parental abuse abound cross-culturally and are embedded into stories taught to children. To understand why child outcomes might be sensitive to levels of relatedness within the household, evolutionary-oriented research targets patterning in parental expenditure in ways predicted to maximize inclusive fitness. In particular, parents are expected to prioritize investments in their biological children. However, stepfamilies are only formed after children experience multiple unfortunate events (e.g. parental loss, poverty), blurring causal interpretations between step-parental presence and stepchild outcomes. Moreover, stepchildren have been shown to be integral to household functioning, caring for their half-siblings and stabilizing relationships. These results challenge narrow views of adaptive behaviour; specifically, that step-parents, unlike biological parents, do no stand to reap fitness benefits from the care that they provide to their stepchildren. To evaluate these critiques, we analyse the survival outcomes of stepchildren. We include over 400 000 individuals from across a natural fertility period (1847-1940) in the United States state of Utah and examine the consequences of parental loss and step-parental introduction. Our analyses yield three key results: (i) exposure to maternal loss in childhood is associated with elevated mortality risk, (ii) parental remarriage does not increase the risk of mortality among stepchildren compared to non-stepchildren who too had lost a parent, and (iii) stepchildren enjoy higher survival than their half-siblings within the same family. Ultimately, this work contributes to the increasingly recognized importance of cooperative relationships among non-kin for childcare and household functioning. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.
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Affiliation(s)
- Ryan Schacht
- Department of Anthropology, East Carolina University, Greenville 27858, USA
| | - Huong Meeks
- Population Science, Huntsman Cancer Institute, University of Utah, Salt Lake City 20270, USA
| | - Alison Fraser
- Population Science, Huntsman Cancer Institute, University of Utah, Salt Lake City 20270, USA
| | - Ken R. Smith
- Population Science, Huntsman Cancer Institute, University of Utah, Salt Lake City 20270, USA
- Department of Family and Consumer Studies, University of Utah, Salt Lake City 20270, USA
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Pettay JE, Chapman SN, Lahdenperä M, Lummaa V. Family dynamics and age-related patterns in marriage probability. EVOL HUM BEHAV 2020. [DOI: 10.1016/j.evolhumbehav.2019.09.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Glynn LM, Baram TZ. The influence of unpredictable, fragmented parental signals on the developing brain. Front Neuroendocrinol 2019; 53:100736. [PMID: 30711600 PMCID: PMC6776465 DOI: 10.1016/j.yfrne.2019.01.002] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 01/04/2019] [Accepted: 01/29/2019] [Indexed: 11/27/2022]
Abstract
Mental illnesses originate early in life, governed by environmental and genetic factors. Because parents are a dominant source of signals to the developing child, parental signals - beginning with maternal signals in utero - are primary contributors to children's mental health. Existing literature on maternal signals has focused almost exclusively on their quality and valence (e.g. maternal depression, sensitivity). Here we identify a novel dimension of maternal signals: their patterns and especially their predictability/unpredictability, as an important determinant of children's neurodevelopment. We find that unpredictable maternal mood and behavior presage risk for child and adolescent psychopathology. In experimental models, fragmented/unpredictable maternal care patterns directly induce aberrant synaptic connectivity and disturbed maturation of cognitive and emotional brain circuits, with commensurate memory problems and anhedonia-like behaviors. Together, our findings across species demonstrate that patterns of maternal signals influence brain circuit maturation, promoting resilience or vulnerability to mental illness.
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Affiliation(s)
- Laura M Glynn
- Department of Psychology, Chapman University, Orange, CA, USA.
| | - Tallie Z Baram
- Department of Anatomy/Neurobiology, University of California-Irvine, Irvine, CA, USA; Department of Pediatrics, University of California-Irvine, Irvine, CA, USA; Department of Neurology, University of California-Irvine, Irvine, CA, USA
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Rattay P, von der Lippe E, Mauz E, Richter F, Hölling H, Lange C, Lampert T. Health and health risk behaviour of adolescents-Differences according to family structure. Results of the German KiGGS cohort study. PLoS One 2018. [PMID: 29513693 PMCID: PMC5841741 DOI: 10.1371/journal.pone.0192968] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Objective This study’s aim was to investigate the association between family structure and different health-related outcomes in adolescence (self-rated health, emotional and behavioural problems, health-related quality of life, regular smoking, and heavy episodic drinking). Furthermore, we analysed the extent to which socio-economic status, family cohesion and the pre-transition health status explain family structure-related health disparities. Methods We used longitudinal data from the first two waves of the German KiGGS cohort study carried out by the Robert Koch Institute (baseline: 2003–2006, follow-up: 2009–2012). The sample comprised 4,692 respondents aged 11 to 17 years. Using data from both waves, effects of family structure on health status at follow-up were calculated applying linear and logistic regression models. Results We found that adolescents continuously living with both birth parents were in good health. Adolescents whose parents separated after the baseline survey, reported poorer health and were more likely to smoke. The transition from stepfamily to single parent family was also associated with a higher risk of regular smoking. Lower health-related quality of life as well as higher scores for emotional and behavioural problems occurred in almost all non-nuclear family structures, although not all effects were statistically significant. No significant effects of family structure on heavy episodic drinking were found. While family cohesion mediated the effects of family structure on adolescents’ health, the mediating effect of socio-economic status was small. After controlling for pre-transition health, the effects were even lower. Conclusions Because the direct effects of family structure on adolescents’ health were small and family cohesion was found to be an important mediator in the association between family structure and adolescents’ health, prevention programmes and interventions should be directed towards the parent–adolescent relationship rather than just the family structure, in order to minimize the psychosocial stress of adolescents during the period of family transition.
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Affiliation(s)
- Petra Rattay
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
- * E-mail:
| | - Elena von der Lippe
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
| | - Elvira Mauz
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
| | - Felicitas Richter
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
| | - Heike Hölling
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
| | - Cornelia Lange
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
| | - Thomas Lampert
- Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany
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Chikhungu LC, Newell ML, Rollins N. Under-five mortality according to maternal survival: a systematic review and meta-analysis. Bull World Health Organ 2017; 95:281-287. [PMID: 28479623 PMCID: PMC5407247 DOI: 10.2471/blt.15.157149] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Revised: 12/07/2016] [Accepted: 12/13/2016] [Indexed: 11/27/2022] Open
Abstract
OBJECTIVE To investigate, within so-called general populations, the relationship between maternal survival and mortality of children younger than five years. METHODS We conducted a systematic review of literature published between January 1990 and November 2016 that reported maternal vital status and the corresponding mortality of children younger than five years. Seven studies were included in a qualitative analysis and four in a random-effects meta-analysis. Summary estimates of the odds of dying by maternal survival were obtained and statistical heterogeneity estimated. Quality of the included studies and evidence was assessed using a Cochrane tool for assessing risk of bias and the Grading of Recommendations Assessment, Development and Evaluation criteria, respectively. FINDINGS Among children younger than five years, those whose mother had died were found to be 4.09 times (95% confidence interval, CI: 2.40-6.98) more likely to die than those with surviving mothers. Due to heterogeneity (I2: 83%), further pooled estimates were not possible. For children that were motherless as a result of maternal mortality, the increased odds of dying ranged from 1.40 (95% CI: 0.47-4.21) to 2.92 (95% CI: 1.21-7.04) among those aged between two and four years, 6.1 (95% CI: 2.27-16.77) to 33.78 (95% CI: 24.21-47.14) for those younger than one year and 4.39 (95% CI: 3.34-5.78) to 51.68 (95% CI: 20.26-131.80) for those younger than six months. CONCLUSION The loss of a mother was associated with increased mortality among children, especially when maternal death occurred in the first year of the child's life.
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Affiliation(s)
- Lana Clara Chikhungu
- School of Languages and Area Studies, University of Portsmouth, Park Building, King Henry 1 Street, Portsmouth, PO1 2DZ, England
| | - Marie-Louise Newell
- Academic Unit of Health and Development, University of Southampton, Southampton, England
| | - Nigel Rollins
- Department of Maternal, Newborn, Child and Adolescent Health, World Health Organization, Geneva, Switzerland
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Why does paternal death accelerate the transition to first marriage in the C18-C19 Krummhörn population? EVOL HUM BEHAV 2017. [DOI: 10.1016/j.evolhumbehav.2016.08.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Thomas MG, Shanley DP, Houston AI, McNamara JM, Mace R, Kirkwood TBL. A dynamic framework for the study of optimal birth intervals reveals the importance of sibling competition and mortality risks. J Evol Biol 2015; 28:885-95. [PMID: 25733026 DOI: 10.1111/jeb.12613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 02/23/2015] [Accepted: 02/25/2015] [Indexed: 11/27/2022]
Abstract
Human reproductive patterns have been well studied, but the mechanisms by which physiology, ecology and existing kin interact to affect the life history need quantification. Here, we create a model to investigate how age-specific interbirth intervals adapt to environmental and intrinsic mortality, and how birth patterns can be shaped by competition and help between siblings. The model provides a flexible framework for studying the processes underlying human reproductive scheduling. We developed a state-based optimality model to determine age-dependent and family-dependent sets of reproductive strategies, including the state of the mother and her offspring. We parameterized the model with realistic mortality curves derived from five human populations. Overall, optimal birth intervals increase until the age of 30 after which they remain relatively constant until the end of the reproductive lifespan. Offspring helping each other does not have much effect on birth intervals. Increasing infant and senescent mortality in different populations decreases interbirth intervals. We show that sibling competition and infant mortality interact to lengthen interbirth intervals. In lower-mortality populations, intense sibling competition pushes births further apart. Varying the adult risk of mortality alone has no effect on birth intervals between populations; competition between offspring drives the differences in birth intervals only when infant mortality is low. These results are relevant to understanding the demographic transition, because our model predicts that sibling competition becomes an important determinant of optimal interbirth intervals only when mortality is low, as in post-transition societies. We do not predict that these effects alone can select for menopause.
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Affiliation(s)
- M G Thomas
- Human Evolutionary Ecology Group, Department of Anthropology, University College London, London, UK
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Willführ K, Myrskylä M. Disease load at conception predicts survival in later epidemics in a historical French-Canadian cohort, suggesting functional trans-generational effects in humans. PLoS One 2014; 9:e93868. [PMID: 24739873 PMCID: PMC3989183 DOI: 10.1371/journal.pone.0093868] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 03/10/2014] [Indexed: 12/02/2022] Open
Abstract
Objective Functional trans-generational and parental effects are potentially important determinants of health in several mammals. For humans, the existing evidence is weak. We investigate whether disease exposure triggers functional trans-generational response effects among humans by analyzing siblings who were conceived under different disease loads, and comparing their mortality in later epidemics. Under functional trans-generational response mechanisms, we expect that those who were conceived under high pathogenic stress load will have relatively low mortality during a later epidemic. Methods We use data from the Registre de la Population du Québec Ancien, which covers the historical population living in St. Lawrence Valley, Québec, Canada. Children born in 1705–1724 were grouped according to their exposure during conception to the measles 1714–15 epidemic. The 1714–15 epidemic was followed by two mortality crises in 1729–1734. The cause of the first crises in 1729 is not exactly known. The second crisis in 1732 was caused by a smallpox epidemic. Using proportional hazard Cox regression models with multivariate adjustment and with fixed-effects approach that compare siblings, we analyze whether mortality in 1729–1734 is affected by exposure to the 1714–15 epidemic. Results Children who were conceived during the peak of the measles epidemic of 1714–15 exhibited significantly lower mortality during the 1729–1734 crisis than those who were born before the 1714–15 epidemic (mortality hazard ratio 0.106, p<.05 in multivariate adjusted models; 0.142 p<.1 in sibling comparison models). Conclusions The results are consistent with a trans-generational mechanism that functionally responds to pathogen stress and suggest that early disease exposure may be protective later in life. Alternative explanations for the mortality patterns are discussed and shown to be problematic.
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Affiliation(s)
- Kai Willführ
- Max Planck Institute for Demographic Research, Rostock, Germany
- * E-mail:
| | - Mikko Myrskylä
- The London School of Economics and Political Science, London, United Kingdom
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Sheppard P, Garcia JR, Sear R. A not-so-grim tale: how childhood family structure influences reproductive and risk-taking outcomes in a historical U.S. Population. PLoS One 2014; 9:e89539. [PMID: 24599234 PMCID: PMC3943735 DOI: 10.1371/journal.pone.0089539] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 01/22/2014] [Indexed: 12/02/2022] Open
Abstract
Childhood family structure has been shown to play an important role in shaping a child's life course development, especially in industrialised societies. One hypothesis which could explain such findings is that parental investment is likely to be diluted in families without both natural parents. Most empirical studies have examined the influence of only one type of family disruption or composition (e.g. father absence) making it difficult to simultaneously compare the effects of different kinds of family structure on children's future outcomes. Here we use a large, rich data source (n = 16,207) collected by Alfred Kinsey and colleagues in the United States from 1938 to 1963, to examine the effects of particular childhood family compositions and compare between them. The dataset further allows us to look at the effects of family structure on an array of traits relating to sexual maturity, reproduction, and risk-taking. Our results show that, for both sexes, living with a single mother or mother and stepfather during childhood was often associated with faster progression to life history events and greater propensity for risk-taking behaviours. However, living with a single father or father and stepmother was typically not significantly different to having both natural parents for these outcomes. Our results withstand adjustment for socioeconomic status, age, ethnicity, age at puberty (where applicable), and sibling configuration. While these results support the hypothesis that early family environment influences subsequent reproductive strategy, the different responses to the presence or absence of different parental figures in the household rearing environment suggests that particular family constructions exert independent influences on childhood outcomes. Our results suggest that father-absent households (i.e. single mothers or mothers and stepfathers) are most highly associated with subsequent fast life history progressions, compared with mother-absent households, and those with two natural parents.
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Affiliation(s)
- Paula Sheppard
- London School of Hygiene and Tropical Medicine, Keppel Street, London, United Kingdom
- * E-mail:
| | - Justin R. Garcia
- The Kinsey Institute for Research in Sex, Gender, and Reproduction, Indiana University, Bloomington, Indiana, United States of America
- Department of Gender Studies, Indiana University, Bloomington, Indiana, United States of America
| | - Rebecca Sear
- London School of Hygiene and Tropical Medicine, Keppel Street, London, United Kingdom
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Störmer C, Lummaa V. Increased mortality exposure within the family rather than individual mortality experiences triggers faster life-history strategies in historic human populations. PLoS One 2014; 9:e83633. [PMID: 24421897 PMCID: PMC3885450 DOI: 10.1371/journal.pone.0083633] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 11/05/2013] [Indexed: 11/18/2022] Open
Abstract
Life History Theory predicts that extrinsic mortality risk is one of the most important factors shaping (human) life histories. Evidence from contemporary populations suggests that individuals confronted with high mortality environments show characteristic traits of fast life-history strategies: they marry and reproduce earlier, have shorter birth intervals and invest less in their offspring. However, little is known of the impact of mortality experiences on the speed of life histories in historical human populations with generally higher mortality risk, and on male life histories in particular. Furthermore, it remains unknown whether individual-level mortality experiences within the family have a greater effect on life-history decisions or family membership explains life-history variation. In a comparative approach using event history analyses, we study the impact of family versus individual-level effects of mortality exposure on two central life-history parameters, ages at first marriage and first birth, in three historical human populations (Germany, Finland, Canada). Mortality experience is measured as the confrontation with sibling deaths within the natal family up to an individual's age of 15. Results show that the speed of life histories is not adjusted according to individual-level mortality experiences but is due to family-level effects. The general finding of lower ages at marriage/reproduction after exposure to higher mortality in the family holds for both females and males. This study provides evidence for the importance of the family environment for reproductive timing while individual-level mortality experiences seem to play only a minor role in reproductive life history decisions in humans.
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Affiliation(s)
- Charlotte Störmer
- Institut für Philosophie, Justus-Liebig Universität Gieβen, Gieβen, Germany
| | - Virpi Lummaa
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
- Wissenschaftskolleg zu Berlin, Berlin, Germany
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