A friend in need is a friend indeed: Need-based sharing, rather than cooperative assortment, predicts experimental resource transfers among Agta hunter-gatherers
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)
Know when to walk away: Contingent movement and the evolution of cooperation
Journal of Theoretical Biology
(2004)- et al.
Reciprocal altruism, rather than kin selection, maintains nepotistic food transfers on an Ache reservation
Evolution and Human Behavior
(2008) Strategies for cooperation in biological markets, especially for humans
Evolution and Human Behavior
(2013)- et al.
Risk and reciprocity in Meriam food sharing
Evolution and Human Behavior
(2002) - et al.
Prosocial signaling and cooperation among Martu hunters
Evolution and Human Behavior
(2015) - et al.
Networks of food sharing reveal the functional significance of multilevel sociality in two hunter-gatherer groups
Current Biology
(2016) - et al.
The evolution of one-shot cooperation: an experiment
Ethology and Sociobiology
(1993) - et al.
“Its a wonderful life”: signaling generosity among the Ache of Paraguay
Evolution and Human Behavior
(2000) The genetical evolution of social behavior
Journal of Theoretical Biology
(1964)- et al.
A tale of two defectors: The importance of standing for evolution of indirect reciprocity
Journal of Theoretical Biology
(2003)
Meat sharing for coalitional support
Evolution and Human Behavior
Competitive helping in online giving
Current Biology
Reputation-based partner choice is an effective alternative to indirect reciprocity in solving social dilemmas
Evolution and Human Behavior
Natural-field dictator game shows no altruistic giving
Evolution and Human Behavior
A marginal model of tolerated theft
Ethology and Sociobiology
Risk-pooling and herd survival: an agent-based model of a Maasai gift-giving system
Human Ecology
The biology of moral systems
Social networks and cooperation in hunter-gatherers
Nature
Tolerated theft, suggestions about the ecology and evolution of sharing, hoarding and scrounging
Social Science Information
Food sharing in vampire bats: Reciprocal help predicts donations more than relatedness or harassment
Proceedings of the Royal Society B
Polygyny without wealth: Popularity in gift games predicts polygyny in BaYaka Pygmies
Royal Society Open Science
The evolution of interspecific mutualisms
Proceedings of the National Academy of Sciences of the United States of America
Cultural considerations in the experience of aging: two African cultures
Sex equality can explain the unique social structure of hunter-gatherer bands
Science
Scaling regression inputs by dividing by two standard deviations
Statistics in Medicine
RICH economic games for networked relationships and communities: development and preliminary validation in Yasawa, Fiji
Field Methods
To give and to give not: the behavioral ecology of human food transfers
Behavioral and Brain Sciences
The Evolution of Contingent Cooperation
Current Anthropology
Food transfers among Hiwi foragers of Venezuela: tests of reciprocity
Human Ecology
Collective action in action: prosocial behavior in and out of the laboratory
American Anthropologist
Meal sharing among the Ye'kwana
Human Nature
Not leaving home: Grandmother and Mosuo male dispersal
Behavioral Ecology
“Economic man” in cross-cultural perspective: Behavioral experiments in 15 small-scale societies
The Behavioral and Brain Sciences
Altruistic cooperation during foraging by the Ache, and the evolved human predisposition to cooperate
Human Nature
Cooperative breeding in South American hunter-gatherers
Proceedings. Biological Sciences/The Royal Society
Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society
Proceedings of the Royal Society B
Mothers and others: the evolutionary origins of mutual understanding
Friendship: development, ecology, and evolution of a relationship
Trade-offs between female food acquisition and child care among hiwi and ache foragers
Human Nature
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2021, Journal of Theoretical BiologyCitation Excerpt :The interpretation of payoffs as survival probabilities also makes sense in cases of resource sharing, e.g., to prevent the death of starving roost mates, vampire bats commonly gift food to those who have been unsuccessful in foraging (Gerald and Wilkinson, 2012; Wilkinson, 1984; Wilkinson, 1988). Also, the Maasai pastoralists of East Africa practice a tradition called osotua: When an environmental disaster such as drought or disease reduces the herd size of a Maasai pastoralist, rather than being forced to sell off the remainder of the herd and leave the profession, they often receive a gift of cattle from another pastoralist to keep their herd size economically viable (Aktipis et al., 2011; Moritz, 2013; Smith et al., 2019). Both of these practices are examples of reciprocal gift giving where saving an at-risk individual from a donor’s surplus enables the recipient to be present and reciprocate the viability-saving gift in the future.