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Cited by 54Evolutionary Psychology and Human BehaviorAnimal Behavior and ReproductionEvolutionary Game Theory and Cooperation

Adult sex ratios and partner scarcity among hunter-gatherers: Implications for dispersal patterns and the evolution of human sociality

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Kramer, Karen L., Schacht, Ryan, Bell, Adrian·2017·Philosophical Transactions of the Royal Society B Biological Sciences
DOI 10.1098/rstb.2016.0316PMC PMC5540858
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Abstract

Small populations are susceptible to high genetic loads and random fluctuations in birth and death rates. While these selective forces can adversely affect their viability, small populations persist across taxa. Here, we investigate the resilience of small groups to demographic uncertainty, and specifically to fluctuations in adult sex ratio (ASR), partner availability and dispersal patterns. Using 25 years of demographic data for two Savannah Pumé groups of South American hunter-gatherers, we show that in small human populations: (i) ASRs fluctuate substantially from year to year, but do not consistently trend in a sex-biased direction; (ii) the primary driver of local variation in partner availability is stochasticity in the sex ratio at maturity; and (iii) dispersal outside of the group is an important behavioural means to mediate locally constrained mating options. To then simulate conditions under which dispersal outside of the local group may have evolved, we develop two mathematical models. Model results predict that if the ASR is biased, the globally rarer sex should disperse. The model's utility is then evaluated by applying our empirical data to this central prediction. The results are consistent with the observed hunter-gatherer pattern of variation in the sex that disperses. Together, these findings offer an alternative explanation to resource provisioning for the evolution of traits central to human sociality (e.g. flexible dispersal, bilocal post-marital residence and cooperation across local groups). We argue that in small populations, looking outside of one's local group is necessary to find a mate and that, motivated by ASR imbalance, the alliances formed to facilitate the movement of partners are an important foundation for the human-typical pattern of network formation across local groups.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

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  • Romantic love is present in almost all human societies, and despite differences in acceptance of polygamy and extra-marital sex across cultures, monogamy remains the dominant marriage type even in groups where polygamy is accepted.

    “Romantic love is present in almost all human societies, and despite differences in acceptance of polygamy and extra-marital sex across cultures, monogamy remains the dominant marriage type even in groups where polygamy is accepted [13,181,182].”

    From The Neurobiology of Love and Pair Bonding from Human and Animal Perspectives (2023) · cites this paper as [181]

    The Savannah Pumé marriage-market section says that most marriages are monogamous despite some polygyny, and the hunter-gatherer social-organization section says polygamy occurs in most hunter-gatherer societies but is usually uncommon (page numbers unavailable). The paper does not address romantic love across human societies or cultural differences in acceptance of extra-marital sex, and its marriage evidence does not establish the claim for human societies generally. (LLM, conf=0.88)

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Research works printed but not linked: 6

  1. Steward JH. 1955 Theory of culture C: the methodology of multilinear evolution. Urbana, IL: University of Illinois Press.
  2. Lee RB, DeVore I. 1968 Problems in the study of hunter -gatherers. In Man the hunter (eds RB Lee, I DeVore), pp. 3-12. Chicago, IL: Aldine.
  3. Meggitt MJ. 1965 Marriage among the Walbiri of Central Australia: a statistical examination. In Aboriginal man in Australia (eds RM Berndt, CH Berndt), pp. 146-166. Sydney, Australia: Angus and Robertson.
  4. Boesch C, Boesch H. 2000 The chimpanzees of the Tai forest. Oxford, UK: Oxford University Press.
  5. Kramer KL, Greaves RD. 2016 Diversity or replace. What happens to wild foods when cultigens are introduced into hunter -gatherer diets. In Why forage? Hunters and gatherers living in the 21st century (eds B Codding, KL Kramer), pp. 15-42. Santa Fe, NM: School of Advanced Research.
  6. Chisholm JS. 1999 Death, hope and sex: steps to an evolutionary ecology of mind and mortality. New York, NY: Cambridge University Press.

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Authors
Kramer, K. L., Schacht, R., & Bell, A.
Affiliations
University of Utah (US)
ORCID
Venue
Philosophical Transactions of the Royal Society B Biological Sciences
Publisher
The Royal Society
Published
2017-07-31
Volume
372
Issue
1729
Pages
20160316
ISSN
  • 0962-8436 (ISSN-L)
  • 1471-2970
DOI
10.1098/rstb.2016.0316
PMC
PMC5540858
OpenAlex
W2740796516
Cited by
54
References
130
Citations by year
2026: 4 · 2025: 5 · 2024: 5 · 2023: 5 · 2022: 4 · 2021: 9 · 2020: 4 · 2019: 5 · 2018: 4 · 2017: 9
FWCI
7.78
Type
journal article
Language
en
Open access
Licence
royalsociety.org/journals/ethics-policies/data-sharing-mining/ (tdm)
Locations
  • Philosophical Transactions of the Royal Society B Biological Sciences (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Science Foundation (0349963; DBS-9123875)
  • L.S.B. Leakey Foundation
Topics
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Evolutionary Psychology and Human Behavior
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Social Sciences › Sociology and Political Science › Evolutionary Game Theory and Cooperation
Keywords
adult sex ratio, dispersal, hunter-gatherers, small populations, demographic stochasticity, human sociality, resource provisioning, intergroup cooperation, coalition formation, network formation
MeSH terms
Adult, Biological Evolution, Female, Humans, Interpersonal Relations, Life Style, Male, Models, Biological, Sex Ratio, Social Behavior, Venezuela, Spouses

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