A friend in need is a friend indeed: Need-based sharing, rather than cooperative assortment, predicts experimental resource transfers among Agta hunter-gatherers

https://doi.org/10.1016/j.evolhumbehav.2018.08.004Get rights and content

Abstract

Despite much theorizing, the evolutionary reasons why humans cooperate extensively with unrelated individuals are still largely unknown. While reciprocity explains many instances of non-kin cooperation, much remains to be understood. A recent suite of models based upon ‘cooperative assortativity’ suggest that non-kin cooperation can evolve if individuals preferentially assort with certain cooperative phenotypes, such as helping those who help others. Here, we test these assortative hypotheses among the Agta, a population of Filipino hunter-gatherers, using an experimental resource allocation game in which individuals divide resources between themselves and camp-mates. Individuals preferentially shared with less cooperative individuals, arguing against cooperative assortativity as a mechanism sustaining resource transfers in this population. Rather, sharing was often based on the recipient's level of need, in addition to kin-based transfers and reciprocal sharing. Contrary to several recent theoretical accounts, in this real-world setting we find no evidence for cooperative assortativity influencing patterns of cooperation. These results may reflect the demands of living in a foraging ecology characterized by high resource stochasticity, necessitating need-based sharing as a system of long-term reciprocity to mitigate repeated subsistence shortfalls.

Introduction

The question of why organisms display cooperative behavior – defined as a behavior which evolved to benefit others (West, Griffin, & Gardner, 2007b) – has been central to biology for over 50 years (Hamilton, 1964; Nowak, 2006). Although kin selection, where cooperation between relatives provides indirect fitness benefits (Hamilton, 1964), and reciprocity, where repeated cooperative interactions lead to greater long-term pay-offs than short-term defection (Trivers, 1971), explain many instances of cooperation throughout the animal kingdom (West, Griffin, & Gardner, 2007a), they appear insufficient to explain the full range of observed cooperative behavior. This is especially true in humans where cooperation is often between unrelated individuals who, particularly in modern market-based economies, may not interact again in the future (Nowak & Sigmund, 2005).

One potential theory to explain the human propensity for cooperation is indirect reciprocity, which suggests that organisms may help others if this increases their reputation as a cooperative individual, resulting in greater cooperation from others in the future (Alexander, 1987; Nowak and Sigmund, 1998, Nowak and Sigmund, 2005; Panchanathan & Boyd, 2003). Crucially, the evolution of indirect reciprocity depends upon preferential cooperation towards these cooperative individuals (‘helping those who help others’). Theories such as competitive altruism (also known as ‘reputation-based partner choice’) make similar predictions, such that cooperative individuals should be preferentially cooperated with (Roberts, 1998; Sylwester & Roberts, 2013). However, the mechanisms are distinct; competitive altruism is based on the principle of signaling cooperativeness to form future mutually-beneficial cooperative ventures, while indirect reciprocity does not require future repeated interactions. Nonetheless, both accounts are theories of ‘cooperative assortativity’, which suggest that cooperation can evolve if individuals preferentially cooperate with cooperative others.

In support of these theories, several lab studies have shown that cooperative individuals receive more help from others, even if they have never previously interacted (Milinski, 2016; Raihani & Barclay, 2016; Sylwester & Roberts, 2013). However, whether these patterns extend to real-world interactions where multiple forms of information can also be used on which to base cooperation, such as kinship or previous interactions, is largely an open question. Field studies have shown that individuals respond to threats to their reputation with increased cooperation (Yoeli, Hoffman, Rand, & Nowak, 2013), while sellers on eBay with a good reputation are more likely to attract customers (Livingston, 2005). However, whether people selectively cooperate with more cooperative individuals remains under-explored in real-world settings. Small-scale populations, where group sizes are small and acts of cooperation frequent – including food-sharing (Gurven, 2004), childcare (Hrdy, 2009), cooperative foraging (Hill, 2002), labor-sharing (Jaeggi, Hooper, Beheim, Kaplan, & Gurven, 2016) and political coalitions (Patton, 2005) – are particularly useful to explore how factors such as cooperativeness, kinship, reciprocity, and other considerations, influence cooperative decision-making. Research in small-scale societies, particularly hunter-gatherers, may also provide insights regarding the social and ecological bases of human cooperative evolution prior to the development of agriculture and large-scale societies (Lee & Daly, 1999).

In several foraging populations the most cooperative individuals, such as those who share the most food, do not necessarily receive more in return (Bliege Bird, Bird, Smith, & Kushnick, 2002; Kaplan & Hill, 1985). Among the Hadza, using a Public Goods Game to measure cooperation, the most cooperative individuals were not more likely to be given resources or nominated as social partners (Apicella, Marlowe, Fowler, & Christakis, 2012). However, among Dominican bay oil producers, individuals with a reputation for cooperativeness were preferred recipients of cooperation (Macfarlan, Remiker, & Quinlan, 2012), while Hiwi who invested more time in foraging received more resources than others (Gurven, 2006). Although this pattern was not found among Ache foragers (Gurven, 2006), Ache who consistently provisioned others were more likely to receive resources when they were sick or injured (Gurven, Allen-Arave, Hill, & Hurtado, 2000). In summary, there is only partial support for models of cooperative assortativity in small-scale societies.

A related theory also based on assortativity posits that cooperation can evolve if agents assort according to cooperative homophily; that is, cooperating with others of a similar cooperative level (Apicella et al., 2012). However, it is unclear why, in the absence of other mechanisms, non-cooperators would preferentially assort with other non-cooperators. While cooperative homophily is an outcome of the above processes based on cooperative assortment, via mechanisms such as ‘walk away’ or partner choice (Aktipis, 2004; Lewis, Vinicius, Strods, Mace, & Migliano, 2014; McNamara, Barta, Fromhage, & Houston, 2008), these mechanisms do not require that defectors actively seek out other defectors. Nonetheless, Hadza individuals were more likely to nominate to live and cooperate with others of a similar cooperative level to themselves, suggesting that assortativity by cooperative homophily may occur and is not merely an outcome of other assortative processes (Apicella et al., 2012). There are therefore two pathways by which cooperative assortment may facilitate the evolution of cooperation: cooperating with the most cooperative individuals (indirect reciprocity and competitive altruism) and cooperating with others of a similar cooperative level (cooperative homophily).

As discussed above, contrary to expectations based on cooperative assortativity in several populations the most cooperative individuals are not preferred cooperative partners. This behavior may reflect need-based sharing, where those in greater need receive more assistance (Aktipis, Cronk, & de Aguiar, 2011). In studies of forager food-sharing, those with a larger family or with low calorific production relative to family consumption, and therefore in greater need, tend to receive more resources (Allen-Arave, Gurven, & Hill, 2008; Gurven, Hill, Kaplan, Hurtado, & Lyles, 2000), while Agta foragers were more likely to receive resources from others if they were unable to procure resources on a given day (Dyble et al., 2016). Consistent with this, Agta in less need were more cooperative in an experimental game (Smith et al., 2016), while lower socioeconomic status has been associated with reduced cooperation in developed countries (Silva & Mace, 2014). Similarly, in an experimental game among Fijians, the most common reason for sharing was the relative need of the recipient (Gervais, 2017).

However, in the absence of other mechanisms need-based sharing is a description of cooperation, not an adaptive evolutionary explanation; a strategy of altruistic donations to those in need, without any subsequent future fitness gain, is unlikely to be selected for. This situation is comparable to the ‘Banker's Paradox’ (Tooby & Cosmides, 1996), where the individuals most in need of a loan (or resources) are the least likely to receive them because they are a greater ‘credit risk’ and less likely to repay the loan. Nonetheless, these observed need-based transfers may be adaptive if they reflect direct reciprocity, where individuals with resources help those in need – as the costs to giving are low and the benefits to the recipient are high – which may be reciprocated in the future (Trivers, 1971). Although research on forager food-sharing has indicated the presence of need-based transfers (Allen-Arave et al., 2008; Gurven, 2004; Hooper, Gurven, Winking, Kaplan, & Hooper, 2015), from these observational studies it is difficult to assess whether these patterns are a result of giving to those in need (i.e., cooperation) or needy individuals taking resources from those with more resources, as predicted by models of tolerated theft (Blurton Jones, 1987; Winterhalder, 1996). Experimental studies which dissociate unsolicited giving from tolerated theft can be used to help answer these questions.

Here we explore resource transfers among Agta hunter-gatherers to test predictions of indirect reciprocity/competitive altruism and cooperative homophily. We use a novel experimental game in which resources are divided between self and known camp-mates. Using this approach, we previously found that individuals preferentially shared resources with both kin and reciprocal partners (Smith et al., 2016). We now extend this analysis to explore how an individual's cooperativeness influences their probability of receiving resources from others. Specifically, we test whether the Agta: i) preferentially share resources with cooperative individuals (in line with theories of indirect reciprocity and competitive altruism); and ii) share resources with others of a similar cooperative level (as predicted by cooperative homophily).

Section snippets

Ethnographic background

This study focuses on two Agta sub-populations, the Palanan Agta (~1000 individuals) and the Maconacon Agta (~250 individuals) from the remote Northern Sierra Madre Natural Park in northeast Luzon, the Philippines. They subsist predominantly as hunter-gatherers, engaging in hunting, fishing and gathering of wild resources, but also in wage or agricultural labor when available. Of the time spent in economic activities, 77% concerned foraging behavior, predominantly fishing (54%), but also

Results

Out of 1312 potential recipients, 492 received resources (37.5%). Of the 32 candidate models, those within two QIC values of the top model are displayed in Table 1. After model averaging, kinship, reciprocity and alter cooperativeness were each associated with sharing resources (Fig. 1; see also table S2 for log-odds estimates and confidence intervals). Consistent with a previous publication (Smith et al., 2016), primary kin (OR = 4.01) and distant kin (OR = 1.78) were more likely to receive

Discussion

These results demonstrate that experimental resource transfers among the Agta do not conform to predictions made by theories of cooperative assortativity. We fail to find evidence for both indirect reciprocity and cooperative homophily; individuals were neither more likely to select cooperative partners or those of a similar cooperative level. Rather, the Agta preferentially shared with less cooperative individuals, which may reflect need-based sharing. Accordingly, we also demonstrate that

Ethics

Ethical clearance was granted by the University Ethics Committee (Ethics code 3086/003). Fieldwork permission was granted by local government units, including the Mayors of the Municipalities visited and from the Department of Environmental and Natural Resources (DENR) as the research took place in a protected area.

Data availability

The data and code associated with this research is available via figshare at https://doi.org/10.6084/m9.figshare.6960998.

Competing interests

We have no competing interests.

Acknowledgements

We thank the Agta communities and research assistants for their help and hospitality in the field.

Funding

This work was supported by the Leverhulme Trust (grant no. RP2011 R045).

References (78)

  • J.Q. Patton

    Meat sharing for coalitional support

    Evolution and Human Behavior

    (2005)
  • N.J. Raihani et al.

    Competitive helping in online giving

    Current Biology

    (2015)
  • K. Sylwester et al.

    Reputation-based partner choice is an effective alternative to indirect reciprocity in solving social dilemmas

    Evolution and Human Behavior

    (2013)
  • J. Winking et al.

    Natural-field dictator game shows no altruistic giving

    Evolution and Human Behavior

    (2013)
  • B. Winterhalder

    A marginal model of tolerated theft

    Ethology and Sociobiology

    (1996)
  • C.A. Aktipis et al.

    Risk-pooling and herd survival: an agent-based model of a Maasai gift-giving system

    Human Ecology

    (2011)
  • R. Alexander

    The biology of moral systems

    (1987)
  • C.L. Apicella et al.

    Social networks and cooperation in hunter-gatherers

    Nature

    (2012)
  • N. Blurton Jones

    Tolerated theft, suggestions about the ecology and evolution of sharing, hoarding and scrounging

    Social Science Information

    (1987)
  • G.G. Carter et al.

    Food sharing in vampire bats: Reciprocal help predicts donations more than relatedness or harassment

    Proceedings of the Royal Society B

    (2013)
  • N. Chaudhary et al.

    Polygyny without wealth: Popularity in gift games predicts polygyny in BaYaka Pygmies

    Royal Society Open Science

    (2015)
  • M. Doebeli et al.

    The evolution of interspecific mutualisms

    Proceedings of the National Academy of Sciences of the United States of America

    (1998)
  • P. Draper et al.

    Cultural considerations in the experience of aging: two African cultures

  • M. Dyble et al.

    Sex equality can explain the unique social structure of hunter-gatherer bands

    Science

    (2015)
  • A. Gelman

    Scaling regression inputs by dividing by two standard deviations

    Statistics in Medicine

    (2008)
  • M.M. Gervais

    RICH economic games for networked relationships and communities: development and preliminary validation in Yasawa, Fiji

    Field Methods

    (2017)
  • M. Gurven

    To give and to give not: the behavioral ecology of human food transfers

    Behavioral and Brain Sciences

    (2004)
  • M. Gurven

    The Evolution of Contingent Cooperation

    Current Anthropology

    (2006)
  • M. Gurven et al.

    Food transfers among Hiwi foragers of Venezuela: tests of reciprocity

    Human Ecology

    (2000)
  • M. Gurven et al.

    Collective action in action: prosocial behavior in and out of the laboratory

    American Anthropologist

    (2008)
  • R. Hames et al.

    Meal sharing among the Ye'kwana

    Human Nature

    (2007)
  • Q.-Q. He et al.

    Not leaving home: Grandmother and Mosuo male dispersal

    Behavioral Ecology

    (2016)
  • J. Henrich et al.

    “Economic man” in cross-cultural perspective: Behavioral experiments in 15 small-scale societies

    The Behavioral and Brain Sciences

    (2005)
  • K.R. Hill

    Altruistic cooperation during foraging by the Ache, and the evolved human predisposition to cooperate

    Human Nature

    (2002)
  • K.R. Hill et al.

    Cooperative breeding in South American hunter-gatherers

    Proceedings. Biological Sciences/The Royal Society

    (2009)
  • P.L. Hooper et al.

    Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society

    Proceedings of the Royal Society B

    (2015)
  • S.B. Hrdy

    Mothers and others: the evolutionary origins of mutual understanding

    (2009)
  • D.J. Hruschka

    Friendship: development, ecology, and evolution of a relationship

    (2010)
  • A.M. Hurtado et al.

    Trade-offs between female food acquisition and child care among hiwi and ache foragers

    Human Nature

    (1992)
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