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

Published online by Cambridge University Press:  14 February 2005

Michael Gurven*
Department of Anthropology, University of California – Santa Barbara, Santa Barbara, CA93106-3210


The transfer of food among group members is a ubiquitous feature of small-scale forager and forager-agricultural populations. The uniqueness of pervasive sharing among humans, especially among unrelated individuals, has led researchers to evaluate numerous hypotheses about the adaptive functions and patterns of sharing in different ecologies. This article attempts to organize available cross-cultural evidence pertaining to several contentious evolutionary models: kin selection, reciprocal altruism, tolerated scrounging, and costly signaling. Debates about the relevance of these models focus primarily on the extent to which individuals exert control over the distribution of foods they acquire, and the extent to which donors receive food or other fitness-enhancing benefits in return for shares given away. Each model can explain some of the variance in sharing patterns within groups, and so generalizations that ignore or deny the importance of any one model may be misleading. Careful multivariate analyses and cross-cultural comparisons of food transfer patterns are therefore necessary tools for assessing aspects of the sexual division of labor, human life history evolution, and the evolution of the family. This article also introduces a framework for better understanding variation in sharing behavior across small-scale traditional societies. I discuss the importance of resource ecology and the degree of coordination in acquisition activities as a key feature that influences sharing behavior.

Research Article
Copyright © Cambridge University Press 2004

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1. Hames (2000) independently defines depth as “sharing intensity,” although from the perspective of a recipient rather than that of a donor. Breadth is defined as “sharing scope.”

2. I use the terms “transfer” and “sharing” interchangeably even though sharing implies intentionality and active giving, whereas transfer is a more neutral description. Ethnographies rarely distinguish between the two usages.

3. This important condition has rarely been tested empirically because estimation of B and C requires knowledge of hunger levels, the utility of macronutrients contained within the food, and any current resource holdings of the donor and potential recipients that are liable to influence the marginal value of receiving shares (Winterhalder 1996a).

4. Within kinship categories of equal r, we should also expect individuals whose reproductive value will increase the most from consuming shares to receive more, than those for whom food has a smaller impact (flow of food from old to young, haves to havenots) (Rogers 1993), because the former yields a greater inclusive fitness benefit to the donor.

5. To the extent that individuals give food to a sick producer, in the expectation of receiving future shares from the producer upon recovery, the donor's initial giving may be thought of as a form of RA, whereas others helping the sick producer recover may be viewed as a form of byproduct mutualism.

6. Although computer simulations reveal that significant correlations between individuals in amounts given and received are possible when tolerated theft is the sole cause of food sharing, correlations greater than 0.2 were only found in highly structured groups of few individuals.

7. It may be argued that individuals who consume all of a resource outside of camp could be punished or ostracized, and that this threat is sufficient to motivate individuals to return to camp with the majority of their catch. However, the likelihood of getting “caught” eating food acquired away from camp may be low, and punishment will not bring back the food already consumed, so few should be willing to incur the costs of punishing hoarding individuals (but see Gintis 2000).

8. Although acquirers may be willing to pay higher costs to defend small resources, if others’ utility for the same food is also high, then they should be willing to pay higher costs to obtain access to portions of these small items.

9. Contrary to these views, Woodburn (1998) argues that Hadza hunters get no benefits from sharing other than the “satisfaction” of completing a “difficult task.”

10. Because of the format of the data available for the Pilaga, I estimated contingency as the correlation between the percentage of family A's consumption (above A's own contribution) provided by family B and the percentage of B's consumption (above B's own contribution) provided by A.

11. In regression analyses of percent given on percent received, the correlation coefficient, r, is equivalent to and carries the same interpretation as the regression coefficient, _.

12. Correlations of general contingency are similar in magnitude to those of specific contingency, although they are less likely to be statistically significant, because the number of observations in general contingency analyses is equal to the number of individuals or families (n). Specific contingency analyses have a sample size of n (n _ 1)/2.

13. Vickery et al. (1991) show that among groups consisting of producers, scroungers, and opportunistic foragers, all three strategies can stably coexist in the same population. Defectors or “scroungers” do not proliferate when producers maintain sufficient control over their kills, when group size is moderate, and when opportunists are not very efficient. Thus, if some scroungers are tolerated (and perhaps provide other benefits), it can still be in producers’ interests to continue acquiring food.

14. If one is known as too generous, others may attempt to exploit them. Thus, people are more likely to give donations when confronted with direct requests, than to give on their own initiative. The desire to avoid requests for money may be an important explanation for anonymous giving to charities (Cicerchi & Weskerna 1991).

15. With a small sample, Dwyer and Minnegal (1993) showed that skilled Kubo hunters did not show higher reproductive success, when measured as the number of legitimate births, than poor hunters.

16. I thank Kim Hill for the analogy of people purchasing small items on credit to build up their credit record so that they can later secure larger credit limits, or bank loans to purchase more expensive items.

17. Path analysis is a useful tool for examining the separate effects of multiple, often codependent, variables related through some causal process (Loehlin 1987). Path values are usually expressed as standardized parameter estimates, where one standard deviation unit increase in the variable at the base of each arrow causes an increase in the variable at the head of each arrow equal to the parameter estimate, also given in standard deviation units. These path values control for all other effects in the model, and allow one to calculate both direct and indirect effects of predictor variables on the outcome variable of interest.

18. When residential bands increase in size because of nonforaging related benefits of grouping (e.g., mating opportunities, proximity to missions or nearby towns, defense against hostile neighbors, etc.), traditional group fissions like those described among the Yanomamo, Ache, Tsimane, and the Penan (Brosius 1990) are more unlikely, and thus, more restricted sharing networks and more stringent contingency can result. As Prost (1983, p. 63) discusses, among the Chácobo, access to market goods has caused larger villages (12–15 nuclear families instead of 6), an absence of traditional fissioning, and a lack of widespread sharing with everyone in the group. He argues that once group size moves beyond 35–45 people, sharing shifts from an intimate “uncalculated” pattern to one based on “rational, reciprocal, cost-benefit calculations.” The fact that individuals have the ability to make this shift and perform well in both small and large group contexts suggests that highly variable group size may have been common in our evolutionary past.

19. Even if TS explains some meat distributions, enforced norms of widespread meat sharing followed by a group of hunters can yield reliable shares of meat over time. Thus, even TS-based sharing can make hunting a viable provisioning strategy.