To Give and to Give Not: The behavioral ecology of human food transfers

Abstract: 211 (Long), 102 (Short)

Main Text: 13,990

References: 3,179

Total Text: 17,482

Michael Gurven

Department of Anthropology

UC-Santa Barbara

Santa Barbara, CA 93106

gurven@anth.ucsb.edu, chatidye@hotmail.com

May 31, 2002

key words: behavioral ecology, costly signaling, cooperation, food sharing, foragers, reciprocal altruism

Long Abstract

The transfer of food among group members is an 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 paper attempts to organize available cross-cultural evidence pertaining to several contentious evolutionary models—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 paper 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.

Short Abstract

This paper attempts to organize available cross-cultural evidence pertaining to several contentious evolutionary models of food transfers in traditional populations—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. This paper introduces a framework for better understanding variation in sharing behavior across small-scale traditional societies, paying particular attention to the importance of resource ecology and the degree of coordination in acquisition activities

1. Introduction

Why do individuals give valuable resources away to others? To give or not to give is a special case of a more general dilemma--why do individuals engage in acts that incur personal costs and benefit others? Behavioral researchers are interested in discovering both the “ultimate” level evolutionary explanations for observed patterns of resource transfer across societies (Winterhalder 1997) and the “proximate” determinants that shape these and other kinds of costly pro-social behavior (Caporael et al. 1989). Anthropologists have focused on explaining the pattern of food transfer among small-scale subsistence economies. Psychologists and economists have tried to understand the motivations for altruistic, “other-regarding” behavior in western societies with market economies (e.g. Rose-Ackerman 1996; Andreoni 2001; Camerer & Thaler 1994). Behavioral biologists have studied several pro-social behaviors including food transfer (e.g. capuchin monkeys, chimpanzees, vampire bats), grooming (e.g. impala, chimpanzees, baboons), foraging (e.g. lions, African wild dogs, killer whales), and group defense. Costly pro-social behavior is viewed by all these researchers as “anomalous” (Dawes & Thaler 1988) because any behavior benefiting others at a substantial personal expense violates the “axiom of rationality” which assumes that higher levels of consumption provide higher individual utility or fitness.

One important source of information for understanding the evolution of pro-social behavior and cooperation is the rich literature on food transfers among people who meet their daily food needs from consuming wild foods and cultigens, with little access to modern markets. These are hunter-gatherers and small-scale forager-agriculturalists. The literature on food transfers among peoples practicing a subsistence economy has grown in the past twenty years. These data are useful for illustrating existing variation in cooperative sharing within and among groups, and may serve as a basis for systematic hypothesis testing.

Research among these groups is critical to resolve debates on the nature of human sociality and cooperation. First, evolutionary psychology emphasizes that the tendency for humans to cooperate, even among strangers in mock scenarios, experiments, and in real life, may be hard-wired due to a long evolutionary history of cooperative big-game hunting and food sharing (e.g. Hoffman et al. 1998; Cosmides & Tooby 1992). Common notions of fairness, equity, and punishment in many domains may have thus been shaped in the sharing context of a hunting and gathering lifestyle (Fehr & Schmidt 1999; Gintis 2000). These researchers should be concerned that assumptions made about hunter-gatherers are well-founded and that empirical results based on western, market-oriented groups are generalizable to a non-market, non-western context.

Second, if the economies of scale and the high levels of specialization found in complex societies were made possible by the development of a pro-social brain developed during a long evolutionary history of hunting and gathering, then understanding the flexibility of “pro-social” behavior may help increase our understanding of how humans have succeeded in generating cultural institutions favoring cooperative outcomes, and subsequently populating the globe. Indeed, it has been suggested that the ability to reap gains from cooperation may be responsible for the recent proliferation of Homo sapiens sapiens (Boyd and Richerson n.d.) at the expense of earlier hominid forms.

Lastly, reinterpretations of men’s hunting and sharing practices as mating rather than as subsistence “strategies”, have called into question traditional notions of the sexual division of labor and the origins of the family (Hawkes 1993; Bird 1999). The extent to which men’s food production and distribution strategies function as forms of family provisioning or as status display has repercussions on future depictions of the evolution of long-term pair bonds (i.e. marriage) and whether the nuclear family is best viewed as a cooperative or competitive enterprise. Whether men are an important source of calories for subsidizing women’s reproduction and child growth within the family can also impact our understanding of the evolution of fundamental human life history traits such as delayed childhood, long post-menopausal lifespans, and large brains (Hawkes et al. 1999; Kaplan et al. 2000).

Despite the growing realization that cooperation among hunter-gatherers is critical to resolving the important issues mentioned above, only a handful of ethnographic studies focus on food transfers, and few of these are systematic or quantitative, making cross-cultural comparison difficult (see below). However, references to food sharing and production in numerous ethnographies can be useful for highlighting observations that are inconsistent with particular hypotheses.

The goal of this paper is to synthesize what is known cross-culturally about within-group food transfers in light of current theory. A complete behavioral ecology of food transfers should explain the function or purpose for food transfers in the first place, as well as the social mechanisms responsible for maintaining different levels of food transfers within populations. It should also predict quantitative aspects of sharing, based on social context, local conditions, and features of resource ecology. Food sharing, for example, has been explicitly modeled as an efficient means of reducing the high daily variance in acquisition (Winterhalder 1986; Kaplan & Hill 1985; Smith 1988). Others have suggested a social purpose for food sharing, where giving acts as an honest signal of donor quality or intent (Smith & Bleige Bird 2000; Gurven et al. 2000b; Zahavi & Zahavi 1998). Since most developed models propose specific benefits to food sharing, we also require a way to specify the relative importance of each hypothetical benefit to observed patterns of food transfers.

Several theoretical models may explain trends in within-group transfers. The most prominent of these include kin selection (KS), reciprocal altruism (RA), tolerated scrounging (TS), and costly signaling (CS) (see Winterhalder 1997). Recent analyses of food sharing have led researchers to believe that several or all of these models might explain some of the variation within the same population (Hill & Kaplan 1993; Winterhalder 1997; Gurven et al. 2000a). Efforts in the past fifteen years have focused on testing alternative hypotheses that can distinguish between these models. To date, most sharing studies have focused on one or few populations. Answers to several key questions can potentially resolve important issues about the general applicability of these models to food sharing in non-market settings. These include: 1) Is (large) game a public good? Do acquirers have control over the distribution of kills? 2) Is food transferred consistently from ‘haves’ to ‘have-nots’? 3) Is giving food contingent on prior or expected future receiving? I survey available evidence on these topics, putting to rest the notion that hunter-gatherer food exchange can easily be explained by any one model. I argue that available evidence cannot rule out reciprocal altruism as an important determinant of most food transfers, nor can it entirely eliminate tolerated scrounging as an explanation of some food transfers. Nonetheless, scenarios of human life history, the sexual division of labor, and the evolution of the family that depend on a tolerated scrounging-based explanation for food sharing are on shaky ground because of the large number of food sharing observations that contradict predictions from that model. Costly signaling of genetic or phenotypic quality may also be an important influence on the production and distribution decisions of certain age and sex classes of individuals. However, many instances of food transfers seem designed to signal a willingness to cooperate, which suggests reciprocity may be a major component of food sharing behavior.

Cross-cultural analyses of sharing require a standard vocabulary for talking about sharing in different populations. Gurven et al. (2001) introduce four terms that describe different aspects of sharing. Sharing depth refers to the percentage of food production given to members of other nuclear families (e.g. 77% of all fish obtained is given to other families). Breadth is the number of other individuals or different families who receive from a given distribution, or alternatively over a given sample period (e.g. on average 4.3 families receive a portion from each deer killed). Equality reflects any disparities in amounts given to different individuals or families in the population (e.g. family B received 6.7% of the food produced by family A but family C received only 1.2% of A's total food production). Balance describes long-term differences in amounts transferred between pairs of individuals or families (e.g. family A gave 47 kg of meat but received back only 12 kg of meat from family B over a 3 month observation period). Each of these measures describes a separate domain of giving or receiving. These four measures allow detailed comparisons of sharing behavior within and across groups, and can therefore facilitate intra-cultural and cross-cultural hypothesis testing.

In this paper, I discuss transfers of all food types[1]. Early observations of extensive meat sharing among social carnivores, the absence of sharing among herbivores and frugivores (Price 1975), and the popularized role of hunting in hominid social evolution (Washburn & Lancaster 1968) have led to a biased focus on game distributions in the sharing literature. Transfers of gathered foods and other food items are either rarely mentioned in ethnographies and food sharing studies, or given only minimal treatment. Even when strong evidence suggests that transfers of game may be explained by a single model, as in the sharing of sea turtles among the Meriam according to tolerated scrounging (Bliege Bird & Bird 1997), identical patterns cannot be inferred for all other components of the diet. If the Meriam reciprocally share yams, bananas, and chicken, or if the Hadza reciprocally share roots and small game--foods which contribute significant calories to the diet--then the fact that large game may be shared according to tolerated scrounging in these societies tells only part of the story of forager food sharing.

2. Models of food sharing

Imagine a male forager with a fresh kill, or a female forager with a basket of fruits or roots. Each must decide (or have decided for them): 1) how much to give to others (depth); 2) How many families should receive a share (breadth) and 3) how much should be given to each of n other locally available individuals (equality)? Each model discussed below gives ceteris paribus conditions which predict when sharing should occur. These differ in the kinds of benefits returned to donors, and the manner in which these benefits are paid.

2.1. Kin selection-based nepotism (KS) Because biological kin share a percentage of ego’s genes through descent, kin-selected food sharing should favor biased transfers toward kin. The conditions which favor kin-selected sharing can be defined by a simple version of Hamilton’s rule (1964), as rB>C. An individual should give to kin when the benefits, B, to a recipient, weighted by Wright’s coefficient of relatedness, r, outweigh costs, C, to the donor.[2] B and C should be measured as impacts on survival and fertility, although these parameters have not been measured in any food sharing study among humans, and in only several cases among other organisms (Wilkinson 1984). It is important to remember that merely showing that kin receive food does not demonstrate nepotism, especially when the majority of one’s neighbors and peers may be related to some degree to any acquirer. A weak test of nepotism predicts that kin should at least receive more than non-kin, and close kin (r=0.5, offspring, parents) should receive more than distant kin (r=0.25, grandparents, grandchildren, r=0.125, first cousins). A stronger test must show that a kin bias is not just due to reciprocal altruism or tolerated scrounging.[3]

2.2. Reciprocal altruism (RA) One may also give portions of food to individuals with whom one has shared with in the past, and is likely to receive shares from in the future. The critical aspect of RA is that giving in the present is an incentive for receipt in the future. This is the concept of contingency (de Waal 1996; Gurven et al. 2000a; Hames 2000). Although tit-for-tat, as modeled via an iterated Prisoner’s Dilemma (Axelrod & Hamilton 1981), is often equated with RA in the game theory literature, tit-for-tat is only one manifestation of RA. A donor who gives a share to an unrelated individual may not know when he may receive a share in return, nor how much he is likely to receive, but may nonetheless give the morsel away, as long as time-discounted expected returns outweigh the costs of the initial sharing. RA, as well as KS and TS (below), are likely when B is significantly greater than C. Thus, the reciprocal transfer of unequal amounts of food is consistent with RA and expected from bargaining theory under a variety of conditions (see also Boyd 1992; Frean 1996). RA found in traditional societies may reflect a type of health insurance, where long-term benefits only sometimes outweigh the costs of giving (Gurven et al. 2000b).[4] Trade is a form of RA where the products given and received are in different currencies. Thus, meat for sex, fish for carbohydrates, honey for social deference, and fruit for assistance in clearing a field are examples of trade. While both trade and in-kind reciprocity yield net benefits to the donor, only in-kind reciprocity has the effect of risk- or variance-reduction in daily intake of specific food types (Hawkes 1993).

2.3. Tolerated scrounging (TS) If individuals get smaller increments of value from consuming additional portions of food, then remaining food portions will eventually be worth more to hungry individuals than to the sated acquirer. When one is unable to maintain control of a resource without paying a substantial cost to defend ‘surplus’ food, an acquirer should cede portions to other individuals if this price of defense is greater than the additional value that could be gained from consuming those extra pieces (Blurton Jones 1987). The acquirer should cede portions until all potential contenders have equal marginal consumption value or utility (Winterhalder 1996). Thus, TS describes food flows from haves to have-nots, when food given away is not contingent on shares received. If a producer can control who receives and how much, or if marginal value is linear or increasing (due to trade for example), then TS is unlikely to explain food transfers. As in RA, medium to large-sized items which are acquired intermittently are most susceptible to sharing by TS.

2.4. Costly signaling (CS) The food quest often involves tasks that require great risk, skill, stamina and vigor. If success in these tasks is due to certain valued characteristics of the acquirer, then engaging in those tasks may represent an honest signal of phenotypic quality. They are honest because they are not easily faked, and they can therefore provide reliable information about some quality of the acquirer. Although less explored, sharing can also be an honest signal of intent, either to initiate or maintain cooperative relations with other individuals. Thus, this different kind of signaling is consistent with RA models (Alexander 1987; Frank 1985; Gurven et al. 2000b).

CS of phenotypic quality is similar to the show-off hypothesis (Hawkes 1991; 1992), but differs in two important ways. First, it does not require TS-based sharing. It therefore does not assume that sharing is determined only by resource package size and asynchronicity in acquisition. Second, CS avoids the second-order collective action problem of who should reward generous sharers, because those that choose sharers as mates, allies, or other social partners, do so as a response to the advertised qualities of those individuals, and NOT as a form of payback for transferred food or as an encouragement for the good provider to stay with the social group (Smith & Bliege Bird 2000). Thus, donors should not resent a lack of giving on behalf of past recipients, nor should recipients feel obliged to return benefits to a donor. Applications of the show-off hypothesis have only been invoked to explain men’s foraging and sharing decisions, and with respect to large game, due to the proposed mating benefits accorded high status, even though signaling benefits may also include alliance building, social support, and mating opportunities for offspring. It is not invoked to explain food transfers by men of other resources (e.g. fruits, roots, honey, firewood) nor of food transfers by women.

3. Predictions of sharing models

The relevance of these models with respect to any particular society is difficult to assess because many predictions are consistent with several of the models. An analysis of the specific costs and benefits of sharing necessary to compare the impact of each model would require a level of estimation unseen in existing quantitative analyses. For this paper, I focus on several key predictions that are most useful for distinguishing among the four models:

3.1. Producer Control An assumption of TS is that producers have little to no control over who receives shares of items they acquire because these items are relinquished to those with greater need. TS asserts that only relative need and power should have any influence on the direction of food transfer. Without producer control, any agent-centered model that tries to understand directed transfers as a function of individual payoffs is suspect, unless the ‘goals’ of the appropriate decision-maker(s) correspond with those of the acquirer. Thus, lack of producer control over redistribution is inconsistent with KS and RA, but is consistent with CS.

3.2. Need The principal determinant of food flows in TS is the need of potential recipients relative to that of the acquirer. Assuming equal ability to defend resources (resource holding potential), food portions should flow to recipients until all possess the same marginal value of consumption (Winterhalder 1996). TS therefore directs food flows from haves to the have-nots, and in the simplest scenario (i.e. no differential information or travel costs, equal marginal values for additional portions), egalitarian distributions among all recipients (including the acquirer) are expected. Any strong bias in food sharing, towards kin (KS), neighbors, specific individuals (RA), etc. is therefore inconsistent with this assumption, unless these preferred recipients show greater relative need than other potential recipients or can obtain benefits at a smaller cost (smaller traveling or monitoring costs, for example). According to CS, we should also not find biased transfers toward privileged others based on need, because the payoffs to signaling derive only from the honest display of production to a wide audience, and not from giving to specific individual.

3.3. Contingency Only RA requires that food be given on condition of expected future receipt. Producers giving more to specific people should receive more back from those people, and similarly, those who do not give should not receive. This requires some form of punishment or ostracism of “defectors”. If shares are returned in the future, the net present value of expected future shares should at least compensate for the present costs of giving. As mentioned above, a contingency effect is generally inconsistent with TS[5]. Although CS does not require contingency among specific pairs of individuals, someone, perhaps other than recipients, is required to provide a benefit to offset the costs of giving up food to signal quality. Thus, according to CS, donors should not be angry or upset if recipients do not return favors, nor should recipients feel obligated to return those favors. It is important to emphasize that CS requires a generalized payback from others, whereas only RA requires a payback from past recipients. KS provides automatic benefits through increased inclusive fitness, while TS avoids a cost and thus provides no benefit.

Much theoretical work and ethnographic discussion on sharing has focused on function--reducing the risk of daily food shortfalls or reducing intake variance due to variance in acquisition (Winterhalder 1986; Smith 1988). It is important to realize that RA, TS, KS, and CS can all produce these effects, thus demonstrating group-level benefits from food sharing practices is not revealing.

The importance of surveying what is known about foragers in relation to these individual-oriented models has become evident in light of the issues raised in the beginning of this paper, particularly the recent arguments over men’s foraging goals (Hawkes 1993; Hill & Kaplan 1993), the sexual division of labor (Bird 1999), and the evolution of a human life history (Kaplan et al. 2000; Hawkes et al. 1998). If foragers lack producer control and if nothing is given in return for that which is received, then the production of large, asynchronously acquired resources, (i.e. wild game or any moderately large, valuable resource) is a partial public good, because others cannot be excluded from receiving shares. Food production, or allocation to the public good, is thus viewed as a collective action problem because non-producers consume portions without paying any production costs. Without producer control and contingency, the traditional notion of hunting as a family provisioning strategy is therefore suspect. It is then argued that men hunt and share game widely as a form of mating effort, vis à vis the show-off hypothesis and CS of phenotypic quality.

TABLE 1. Worldwide Ethnographic Sample

HUNTER-GATHERERS (31)

Africa North America

Hadza (Hawkes et al. 1991; 2001; Dogrib (Helm 1972)

Marlowe n.d.) Central Eskimo (Damas 1972; Balikci 1970)

Dobe !Kung (Lee 1972) Mistassini Cree (Rogers 1972)

G/wi Bushmen (Silberbauer 1981; Washo (Price 1975)

Tanaka 1980) Tolowa (Gould 1981)

Nyae Nyae !Kung (Marshall 1976) Tututni (Gould 1981)

Kutse Basarwa (Kent 1993) Coast Yurok (Gould 1981)

Mbuti Pygmies (Ichikawa 1983; Shoshoni (Fowler 1986; Steward 1938)

Harako 1976)

Efe Pygmies (Bailey 1991)

Aka Pygmies (Bahuchet 1990;

Kitanishi 1996; 1998)

South America Australia

Pilaga (Henry 1951) Gunwinggu (Altman 1987)

Yora/Yaminahua (Hill and Kaplan 1989) W. Desert Aborig. (Gould 1981; Myers 1988)

Ache (Kaplan and Hill 1984; 1985) Yolngu (Peterson 1993)

Siriono (Holmberg 1969) Pintupi (Myers 1988)

Hiwi (Gurven et al. 2000a)

Kaingang (Henry 1941) Southeast Asia

Ayoreo (Bugos and McCarthy 1984) Agta (Peterson 1978; Griffin 1984)

Lengua (Grubb 1911) Onge (Bose 1964)

Batek (Semang) (Endicott 1988)

FORAGER-AGRICULTURALISTS (11)

South America Africa

Maimande (Aspelin 1979) Basarwa Kung (Cashdan 1985)

Yanomamo (Hames 2000; 1990) Tswana/Kalanga (Cashdan 1985)

Yuqui (Stearman 1989)

Ache (Gurven et al. 2000b; 2001; 2002)

Chácobo (Prost 1980) Islands

Ifaluk (Betzig and Turke 1986; Betzig 1988;

Sosis 1997)

Meriam (Bliege Bird and Bird 1997;

Bliege Bird et al. n.d.)

Batak (Cadelina 1982)

Lamalera (Alvard and Nolin 2002)

4. The cross-cultural record

Table 1 lists all the hunter-gatherer and forager-agriculturalist groups for which I was able to find explicit quantitative or qualitative descriptions of food transfer patterns. Quantitative studies are in italics. Of the 41 groups listed, 29% are from South America, 24% from Africa, and the remaining from Australia, North America, and Southeast Asia. While these percentages may not accurately reflect the worldwide representation of foragers and small-scale non-market economies, this list includes all available studies that I could find in the literature. Information on each topic discussed below was not available for all groups listed in Table 1, and so omission of a group for a specific topic does not necessarily imply an absence of that behavior in the group.

4.1. Do producers have control over distributions?

Descriptions of widespread sharing where everyone present in camp sometimes receives portions of a kill (e.g. Western Desert Aborigines, Ache, G/wi), where kills are handed over and butchered by individuals other than the hunter (e.g. Ache, Efe Pygmies, Gunwinggu, Ona), where specific cultural rules delineate which classes of individuals receive specific portions of game animals (e.g. Copper Eskimo, Aka Pygmies, Gunwinggu and Western Desert Aborigines), or where hunters receive no more than other band members (Ache, Batak), have led some investigators to conclude that hunters exert little influence over the distribution of game (Dowling 1968; Hawkes 1993; Bird 1999). Without producer control, the question “Why bother sharing if the spoils go to other people?” is a legitimate concern because food may then be viewed as a public good. As argued above, if exclusions are possible due to a moderate level of producer control over the character of distributions, then game is not a public good. Observing the extent of producer control is confounded by a lack of understanding how distribution decisions are made in the context of the conflicting push and pull of interested parties. It is also confounded by the implicit assumptions that a lack of control is signified by a hunter’s receiving 1/n and that complete control is viewed as an ability to hoard 100% of a resource. However, keeping 1/n does not signify a lack of control if the acquirer decides that 1/n is the optimal portion to keep, given the expected payoffs to sharing. Even when hunters relinquish complete control of game, as among the Ache, such abandonment may be voluntary, as Ache do not relinquish control when at the reservation (Gurven et al. 2002).

Producer control of distribution is indicated by several common ethnographic distribution patterns. Many studies report biased distributions, preferential shares to acquirers and their families, or more frequent sharing to close kin outside the nuclear family at the expense of more distant kin and unrelated individuals [Gunwinggu (Altman 1987), Copper and Netsilik Eskimo (Damas 1972), Pilaga (Henry 1951), Hiwi (Gurven et al. 2000a), Kaingang (Henry 1941), Batek (Endicott 1988), Pintupi (Myers 1988), Washo (Price 1975), Yanomamo (Hames 1990), Basarwa (Cashdan 1982), Ifaluk (Sosis 1997), Agta (Griffin 1984), Ache (at reservation) (Gurven et al. 2001), and Machiguenga (Kaplan pers comm)]. While it is possible that close kin may be more likely to live in closer proximity than other individuals (and hence more likely to demand shares), the few studies which examine both kinship and distance reveal that close kin receive more than other individuals, even when controlling for residential distance [Hiwi (Gurven et al. 2000a, Ache (at settlement) (Gurven et al. 2001)]. An additional bias common in many forager societies is the bride service tradition, where young men must provide meat for their new wife and in-laws [!Kung (Leacock & Lee 1980); Yanomamo (Ritchie 1991); Hadza (Woodburn 1998)].

Expectations of sharing are usually greatest in camp, which leaves the option for some hunters to consume small portions of their catch at or near the kill site prior to transporting it back to a communal camp. Indeed, hunters are frequently allowed to consume internal organs and marrow from animals they kill at the kill site [e.g. the !Kung (Speth 1990) the G/wi (Silberbauer 1981), the Nyae Nyae !Kung (Marshall 1976), the Hadza (Woodburn 1998) and the Batek (Endicott 1988)], where “no one begrudges them this right” (ibid:117). Several Lengua men gorged themselves full of ostrich eggs, returning to camp with only a few, so that they wouldn’t have to share with those who were not producing enough (Grubb 1911:190). Ache hunters, for example, could potentially bring family members to cook and consume meat at the kill site, but this never happens. In all of these groups, much food is transported to camp, an observation that is consistent with a desire to share food[6].

A higher percentage of big game is distributed to more families than small game in all groups where the effect of package size has been examined [Hiwi (Gurven et al. 2000a, Ache (Kaplan and Hill 1985; Gurven et al. n.d.), Dobe !Kung (Lee 1979), Kutse (Kent 1993), Yanomamo (Hames 1990), G/wi (Silberbauer 1981), Nyae Nyae Kung (Marshall 1976), Ifaluk (Sosis 1997), Aka (Kitanishi 1998)], which suggests either greater opportunities for hunters to gain benefits through increased exchange (due in part to diminishing returns to hoarding for the acquirer) or that producers have increasingly less control over distributions. Even if greater sharing depth and breadth were indicative of declining producer control, producers often receive significantly more than 1/n, thereby making the production of large resource packages worthwhile. During one season in 1987, a Gunwinggu family composed only 20% of the band, provided 41% of the band’s total calories, and kept twice as much as the other household cluster (Altman 1987). Similarly, Hiwi and Ache families represented 3% and 5% of their village settlement populations in 1990 and 1998, and kept 20% or more of what they acquired, including meat, giving the rest to fewer than 6 other nuclear families (out of 23 and 36, respectively) (Gurven et al. 2000ab). While Yora families divide game equally on forest trips, they keep about 40% of acquired game at the village settlement, giving the rest to 3 (out of 10) other families (Hill & Kaplan 1989). About 69% of acquired meat was kept within the family of Yuqui hunters, with the rest given to about 5 other hunters out of 15 (Stearman 1989). Yanomamo hunters kept twice as much food for their families than was given to each other family (Hames 2000). Similarly, Hadza hunters’ share of large game items are almost twice as large as those given to others (Hawkes et al. 2001).

If hunger gives others claim to shares, thereby reducing producer control, then it is unclear why smaller resource items are frequently kept within the nuclear family of the acquirer even though others may be hungry. Small game, such as steenbok, duikers, and tortoises, are frequently consumed within an acquirer’s family among the Dobe !Kung (Lee 1972) or those “people close to the hunter” among the G/wi (Silberbauer 1981), even though the size of some of these small animals is comparable to those which observe wide sharing among other groups, such as the Ache. Thus, as reported among Western Desert Aborigines, even small game meat is distributed as tiny portions so that “everyone in camp gets a share” (Gould 1981:432).

Others’ hunger levels should also increase during periods of food scarcity. According to TS, any increased demand for food should increase the breadth and/or depth of sharing. Case reports of the Ik (Turnbull 1972), the Ojibwa Indians (Bishop 1978) and the Northern Shoshone (Moulton & Dunlay 1983) however, demonstrate less sharing during stressful times. The Batak share with significantly fewer households during the pre-harvest season when food is scarce. The average geographical distance between sharing households during this time is about one-half the distance during more plentiful seasons (Cadelina 1982).

Another common pattern among the subset of groups where men hunt cooperatively is for game to be distributed initially among all participants in the hunt [Netsilik Eskimo (Damas 1972), Nyae Nyae !Kung (Marshall 1976), NW Coast Indians (Gould 1981), Ifaluk (Sosis 1997), Pintupi (Myers 1988), Washo (Price 1975), Mbuti (Ichikawa 1983), Aka (Kitanishi 1996; 1998), Efe (Bailey 1991), Shoshone and Paiute (Fowler 1986), Hiwi (Hill pers. comm.)]. Several ethnographies are explicit about subsequent exclusive ownership of meat shares upon initial receipt in a primary distribution, regardless of whether or not others have received their own shares [Mbuti (Ichikawa 1983), Nyae Nyae !Kung (Marshall 1976), Kaingang (Henry 1941), Efe (Bailey 1991)]. This is exemplified by Marshall’s statement about the Nyae Nyae !Kung that “when an individual receives a portion of meat, he owns it outright for himself. He may give and share it further as he wishes, but it never becomes family or group property” (1976:363). Similarly, Bailey writes that while cooperatively acquired game is shared among Efe hunters, meat acquired by solitary hunters is “entirely his to allocate as he pleases” (Bailey 1991:100).

While frequent protestations often make distributions the subject of strife, the occurrence of demand sharing (Peterson 1993; Woodburn 1998) does not imply a lack of producer control due to high costs of defending resources. Henry (1951) reports that Pilaga families are able to bias food towards specific households despite the objections of other individuals. Among the Siriono, “one may be accused of hoarding food, but the other members of the extended family can do little about it except to go out and look for their own” (Holmberg 1969:88). People do not have automatic claim to others’ acquisition among the Pintupi, where “sharing often takes place only on request” (Myers 1988). Aka Pygmies often do not share food, and “…distribution within the camp is actually voluntary…the family chooses whether or not it shares its meals and with whom it shares…temporary disappointment is evident when a household is left out of a distribution” (Bahuchet 1990:38). While the Agta are reported to share most foods equally among available families, they often set aside separate portions of meat to be used in trading for carbohydrates with non-Agta neighbors (Griffin 1984).

4.2. Does food flow according to need?

Much has been written about the emphasis placed on generosity, and the “moral obligation” to help others in need among traditional societies (Barnard and Woodburn 1988), exemplified by the Chácobo proverb, “If you are a human being, then you will share what you have with those who are in need” (Prost 1980:64). Marshall writes that among the Nyae Nyae !Kung “…if there is hunger, it is commonly shared. There are no distinct haves and have-nots” (1976:357). The complementary side of praising generosity is condemning stinginess. “The most serious accusations one !Kung can level against another are the charge of stinginess and the charge of arrogance.” (Lee 1979:458). Similarly, one of the most serious Ache insults is to call somebody mella (a non-giver). The Yanomamo are “so preoccupied with the possessions (including food) of others…anyone who has more than a day’s supply of anything is a potential target of an accusation of stinginess if he does not share” (Hames 1990:103). Lengua who insist on keeping food for themselves are similarly “hated and terrorized by others” (Grubb 1911:190). These descriptions support the view that social dynamics in small-scale societies are organized by an ethic of ‘assertive’ egalitarianism (Woodburn 1982) and that ‘demand sharing’ equalizes differences due to production ability. Because strong pooling norms reduce variance in benefits as well as costs, certain leveling mechanisms have been proposed as cultural means of limiting the arrogance and wealth accumulation of hunters (or anyone for that matter) (Dowling 1968; Woodburn 1982; Wiessner 1996). These include ridicule of a hunter’s prowess [!Kung (Lee 1979)], taboos against hunters consuming portions of their own kills [e.g., Ache (Clastres 1972), Hadza (Woodburn 1982), Ona (Bridges 1948)], and explicit sharing rules [e.g., Central Eskimo (Damas 1972), Gunwinggu (Altman 1987)]. Additionally, it has often been stated that refusing to give shares to others upon request is “the ultimate sin” (Prost 1980:52), and that even when food is not obligatorily indebted to others, requests for shares are rarely denied [e.g. Batek (Endicott 1988), Pintupi (Myers 1988), Kaingang (Henry 1941), Kutse (Kent 1993)].

These cultural notions manifest themselves in ways that encourage egalitarianism. Anecdotes of horticulture failing among the Hadza (Woodburn 1982), Batek (Endicott 1988), Hiwi (Hill pers. comm.), and Agta (Headland 1986) due to incessant pressures on the hardest-working to give away the bulk of their production, are consistent with assertive egalitarianism. The fact that men still hunt even though some selfish benefits may be denied via various leveling mechanisms suggests that hunters either retain additional portions (as argued above), gain other benefits through reciprocity or trade, or obtain mating or other benefits through costly signaling (see below)[7].

While norms regarding ideal distributions are prevalent cross-culturally, they do not necessarily eliminate producer control or producer advantage, nor do they indicate that givers do not gain any advantage by helping needy individuals. Cultural rules or expectations need not mesh with daily transactions (Pennington & Harpending 1993). Indeed, Altman and Peterson (1988) report that explicit sharing rules for dividing large macropods among the Gunwinggu account for only 50% of game items. Among the Aka, estimates of the percentage of different game items shared to other individuals differed substantially from the amounts predicted by sharing rules (Kitanishi 1998). Extensive descriptions of quarrels over food distributions among the !Kung, the Siriono, and the Yanomamo are also testament to the fact that rules do not always cleanly predict behavioral outcomes.

There is quantitative evidence that giving does indeed reflect the relative need of recipients. Among Ache (Kaplan & Hill 1985; Gurven et al. 2001), Maimande (Aspelin 1979) and Hiwi (Gurven et al. 2000), shares are given in proportion to the number of consumers within the recipient family. These observations are consistent with both TS and RA. Families with high dependency tend to be net consumers while those with low dependency are net producers among the Batak (Cadelina 1982). Among the G/wi, the largest shares of game are first given to families with kids, then to those without kids, and the smallest shares are given to single individuals (Silberbauer 1981). There is also some description of younger Ache, Gunwinggu, Efe, Kutse and Agta hunters ceding portions of game to older men who may bias distributions in their favor, with the end result that older hunters with more children (and hence greater caloric demand) benefit more from sharing than do the younger hunters with small or no families. Furthermore, prolific hunters often subsidize other band members, and often give away more than they receive back [Yuqui (Stearman 1989), Ache (Gurven et al. 2000b), Hiwi (Gurven et al. 2000a), Kutse (Kent 1993), Efe (Bailey 1991)]. Even at a permanent Ache settlement where cultivated foods constitute the majority of the daily diet, higher producers give an increasingly higher proportion of their production away to members outside their nuclear family (unpublished data), consistent with the notion of a progressive tax on income (Woodburn 1982).

There is, however, little question that limitations on the kinds and amounts of benefits that accrue to good hunters exist, and that self-interest models which ignore constraints of group living will not completely explain variation in food sharing patterns. Group living implies a series of trade-offs where high producers may compromise their production in exchange for some other group-derived benefit, such as defense, trade, and increased mating access. If individuals are free to move among bands or villages (except for transaction costs), then these group-derived benefits (and not risk-reduction) must influence the perceived costs and benefits of sharing decisions when donors give more than they receive. Empirical studies need to explore the possibility that consistently generous individuals may receive prestige, support, or social insurance (discussed below), and that these social benefits have fitness consequences, before concluding that generous donors give according to TS. Alternatively, recent cultural group selection models may also offer insight into the evolution of costly giving, as opposed to other costly displays of phenotypic quality (Wilson 1998; Boyd & Richerson 2001).

Need is a salient component of sharing, but it does not dictate the entire character of daily distributions. Necessity for food can be due to differential abilities, knowledge, luck, or high dependency ratio, and there is no reason to expect the same patterns of distribution for all four causes of need (see Section 5). Furthermore, biases in distributions mentioned in the previous section, as well as the influence of proximate factors, such as population size and privacy, can all influence the salience of need in food transfer decisions.

Need may also not correlate with sharing outcomes when individuals differ in what is referred to by biologists as ‘resource holding potential’ (RHP). RHP includes physical prowess, authority, social influence, or any ability that can allow an individual to defend resources more easily, or to extort resources from other less powerful individuals. According to TS, only powerful individuals can avoid relinquishing shares to hungry individuals. RHP has never been measured in any society, especially since any single factor, such as muscular strength, fighting ability, or age, may not accurately predict RHP. Many observations, however, are inconsistent with RHP-based predictions. People often save plates of food for absent individuals, even though other group members may not receive any portions. Hungry children often receive food from adults other than their parents. Village chiefs and influential individuals often give away more food than they receive.

4.3. Do donors get back more utility than they give away?

The notion that giving is conditional upon expectations of future receiving (based perhaps on past receiving) is difficult to test. Sahlins’s (1972) “generalized reciprocity” implies that in-flows and out-flows should balance over the course of people’s lives, but that daily giving is done without reference to any accounting procedure. As pointed out by Hawkes (1992), this general anthropological description of reciprocity differs from the way RA is commonly used among biologists and evolutionary anthropologists. The maintenance of RA requires that beneficiaries give a return benefit back to the original donor. Several factors are crucial in determining how much is returned to pay back a donor: the cost to the donor of giving, the benefit to the recipient, the time delay into the future when a benefit is returned, and the benefit to the original donor of receiving in the future. A suitable condition for RA occurs when benefits to recipients greatly outweigh the costs to donors—precisely the need-based condition compatible with TS and KS. One problem with identifying and measuring contingency lies in the choice of an appropriate time frame over which reciprocation should occur (Hawkes 1992; Gurven et al. 2000a). At which point is a lack of reciprocation considered a defection? Does giving back half of what one was given constitute an act of reciprocation or defection?

Economic bargaining theory offers an appropriate way for understanding contingency and RA (Ståhl 1972; Hill & Kaplan 1993; Sosis 1998; Gurven et al. 2000a). Donors should give as long as the expected future benefit outweighs the current costs of giving relative to other options; thus, the exchange of unequal quantities is often consistent with RA. Figure 1 shows an Edgeworth box representing the exchange of A’s present production for B’s future production. Concave curves radiating from the lower left and upper right corners represent the utility A and B derive from consuming some combination of A’s (or B’s) present and B’s (or A’s) future production. The oval region in the interior represents the “bargaining zone”. A and B can both expect to gain if the final bargain is struck anywhere in this region, although they may not benefit equally. Where the final bargain is struck should be influenced by the relative bargaining power of the interactants, which reflects the expected cost from giving and benefit from receiving a specific quantity of food. These costs and benefits could vary with the amount of existing wealth, influence, production ability, status, or number of dependent offspring. Thus, exchange does not have to be perfectly balanced in order to be perceived as beneficial to involved parties and maintained by RA.

FIGURE 1. An Edgeworth Box of Food Exchange

The proportion of receiving that is contingent upon giving has been estimated in only seven groups, four of which are located in South America: the Hiwi (Gurven et al. 2000), Ache (Gurven et al. 2000b), Yanomamo (Hames 2000), Pilaga (my analysis based on data from Henry 1951), Aka (my analysis based on data from Kitanishi 1998), Hadza (my analysis based on Appendix A, Hawkes et al. 2001), and Meriam (Bliege Bird et al. n.d.). Contingency is calculated as the correlation between the amount or percent of total production A gives B with the amount or percent B gives A, over a sample period which usually ranges from several weeks to several months[8]. Most correlations given in Table 2 are statistically significant and range from 0.16 to 0.60 when considering the exchange of any food item for any other food item. Limiting the foods to wild game, the range is 0.10 to 0.46, with no contingency found for Ache meat sharing on temporary foraging trips out from a reservation settlement or Meriam turtle sharing (see 8.2). Measurement error aside, these numbers suggest that an acquirer giving away 1 kg of food or 1% of his production can expect to receive only about 0.33 kg or 0.33% of a recipient’s production in return. It seems reasonable to conclude that contingency does exist (cf. Hawkes and Bird 2002), but without the appropriate theory, it is not yet possible to determine whether these contingency levels support RA or are instead suggestive of something else.

TABLE 2. Measures of contingency

		correlation, r
	Group	all food		meat		Source
1)	Hiwi	0.18	^***	0.34	^***	Gurven et al. 2000a
2)	Ache (forest)	0.26	^*	-0.16		Gurven et al. n.d.b
	Ache (settlement)	0.36	^***	0.10	^*	Gurven et al. n.d.a
3)	Yanomamo (1)	0.16	^*	-		Hames 2000
	Yanomamo (2)	0.21	^*	-		Hames 2000
	Yanomamo (3)	0.29	^*	-		Hames 2000
	Yanomamo (4)	0.50	^*	-		Hames 2000
4)	Pilaga	0.42	^*	-		Henry 1951
5)	Aka	0.60	^**	0.44	^***	Kitanishi 1998
6)	Hadza	-		0.46	^***	Hawkes et al. 2001
7)	Meriam	0.14		0.01		Bliege Bird et al. n.d.

*** = p<0.0001, ** = p<0.001, * = p<0.05

Note: Meriam meat refers to turtle meat exchanges only

Several ethnographers have also provided anecdotal support for contingency. Among the Pintupi, “large game is distributed inter-domestically to members of the residential group who have shared with the hunter in the past” (Myers 1988). One Maimande informant told Aspelin that “if one doesn’t give, one doesn’t get in return…some people are specifically excluded from most distributions because they never or only rarely give any of their products to us” (Aspelin 1979:317). Similarly, “the return may be made at a later date but it will be expected” among Agta sharing to those outside the household cluster (Peterson 1978:40). There are also hints of contingency among several of the more assertively egalitarian groups. The “giving of food does involve an obligation on the part of the recipient to return food to the donor at some future date” among the Siriono (Holmberg 1969:45) and “…something must be given in return for what is received” among the G/wi (Silberbauer 1981:463).

Conversely, the ethnographic literature also contains references to contingency that are consistent with generalized reciprocity, but may not be with RA. The Batek, for example, explain that giving and receiving “balance out over the long run” (i.e. lifespan) (Endicott 1988:118), while giving and receiving among the Kaingang is “not a matter of checks and balances…their understanding of reciprocity is in terms of lifelong symbiosis, not in terms of balanced exchanges” (Henry 1941:101). Whether the benefits that accrue after the very long delays associated with generalized reciprocity outweigh the opportunity costs to giving in the present is an important question worthy of future research.

General contingency, or the correlation between the total amount given away to others and the total amount received from all others, has been measured in six societies-Ache (Gurven et al. 2002), Hiwi (unpublished analysis), Meriam (Bliege-Bird and Bird 1997), Pilaga (my analysis of Henry 1951), Yanomamo (Hames 2000), and Hadza (Hawkes et al. 2001). These studies showed mixed support for general balance[9]. While a lack of specific contingency contradicts RA, the presence of general contingency is consistent with indirect reciprocity (Alexander 1979; Boyd & Richerson 1989), where individuals other than direct recipients may confer benefits upon a donor, and with a form of CS where the return benefit to the donor is food. If the return benefit is in another currency, such as increased mating opportunities, then a lack of general balance is not inconsistent with CS.

Ethnographies often highlight anecdotes suggestive of trade rather than indirect reciprocity. For example, Pintupi women give food production to “those who looked after the children while she was away” (Myers 1988). The best Yuqui and Tsimane hunters appear to work less in garden labor, trading portions of their kills for garden products (Stearman 1989; Chicchón 1992). Manioc is given to Kuikuyu who do not have manioc fields, in exchange for helping with weeding tasks (Carneiro 1983). Holmberg (1969) explains that Siriono men give food to their wives in exchange for sex, and that more food is given to younger wives, with whom the husbands desire to have more sex. Yanomamo men also give meat in expectation of receiving sex (Ritchie 1995:190-93).

4.4. Are slackers punished?

Another aspect of contingency is that those who do not share, who do not share enough, or who do not produce food should somehow be “punished” for their lack of cooperation, either through the withholding of shares, social ostracism, or by village fission. While punishment has not been systematically studied in any group, there are abundant illustrative anecdotes of punishment from the ethnographic literature. For example, one Pilaga family temporarily left the village in response to giving twice as frequently as it was receiving food from another family, consistent with their common complaint, “I have given something to him but he has not given to me” (Henry 1951:199). Although Maimande food distributions appear egalitarian (quantities given to each family is inversely proportional to number of families present), Aspelin (1979) notes several cases where one unproductive family with a precarious position in the village was frequently excluded from receiving shares. Altman (1987:147) describes a collusion between two Gunwinggu family clusters to share less food to a third cluster who was “not producing enough”. This sanction induced higher production and sharing by the third cluster, wherein the other two family clusters resumed normal relations. Among the Washo, a “person who would not share with others of the same household, or who was generally stingy would not be included in the networks of sharing and would be ‘talked out’ of his household” (Price 1975:16). Baksh & Johnson (1990) relate a similar anecdote where a household that “did not like to work cooperatively, or participate in communal undertakings” was driven out of the village. An unproductive family “quickly gets pressure to contribute its own share” among the Agta, where social ostracism ultimately forces them to relocate (Griffin 1984:20). Bridges (1948:374-75) describes an incident among the Ona where a hunter who didn’t share a small bird was ridiculed and humiliated with mocking bird calls by other men for years. Among the Netsilik Eskimo studied by Balikci (1970:177), “lazy hunters were barely tolerated by the community. They were the objects of back biting and ostracism…until the opportunity came for an open quarrel. Stingy men who shared in a niggardly manner were treated similarly”. A similar anecdote is described among the Canadian Utku, where a stingy family was relocated at some distance from the core community (Briggs 1970:219-23). Finally, Bertoni (1941:39) describes how a greedy Ache hunter, getting fat from killing game and not sharing it with his thin wife, angered so many people in camp that a group of men killed him “by spearing him and then clubbing him to death”.

Several anecdotes, however, demonstrate tolerance for either low producing individuals or for violations of implicit social contracts. Several Chácobo households who consistently under-produced for several years due to “poor planning, indifference, or laziness” received more than they gave away, and “were tolerated…they were never expelled or ostracized from the community” (Prost 1980:52). Instances of pinenut stealing were never confronted due to a “desire to keep peace” among the Kaingang, although Henry also contends that “many of the conflicts within the extended families arise out of some failure to live up to the ideal of constant helpfulness and support” (1941:101). Among the Siriono, older individuals sometimes steal food late at night (although they deny it), and are never punished for their actions, although they are often the subject of condescending gossip (Holmberg 1969). Endicott (1988:119) describes several able-bodied adults who “seemed to take more out of the sharing network than they put in”. After asking several informants why they did not try to expel one of these lazy individuals, they responded “because he is a Batek”. It is interesting to note that the spouses of two of the three slackers boosted their own work effort in an attempt to compensate for the laziness of their husbands.

Anecdotes of punishment reveal the difficulties in assigning labels of “cheater” or “defector” to certain individuals, and of subsequently measuring contingency. Because the quantity of food A gives B is equal to the product of A’s production and the proportion of A’s production given to B, a failure to reciprocate can be due to either low production or an unwillingness to share. With little producer control, a failure to share is equivalent to a failure to produce. As mentioned previously, low production can result from controllable factors such as low time investment due to laziness or other time-consuming responsibilities and from uncontrollable factors, including bad luck, sickness or injury, and low ability. We might expect less tolerance for low production due to controllable factors, although it may not always be easy to distinguish the cause of poor production. However, in small groups with little privacy and much gossip, long-term deceptions are unlikely. Although we might a priori predict that only quantities exchanged matter, several bargaining experiments reveal that intentions also matter in determining fair outcomes (Blount 1995). The fact that pregnant Ache and Hadza women reduce their work effort (Hurtado et al. 1985), and are instead subsidized by other Ache and Hadza, whereas reduced work effort might not normally be tolerated (as suggested by its rarity and by informant reports), lends support to the notion that causation can influence decisions based on fairness (see 8.2). Indeed, Gurven et al. (2002) argue that the sharing of non-meat items and cultigens shows high contingency, when measured in terms of quantities of food exchanged across pairs of families, while the sharing of meat items often shows low or no quantity-based contingency (see below). Success rates and quantities of foraged foods (e.g. fruits and roots) produced are heavily dependent on the amount of time spent in their acquisition, while luck and random factors have a much greater influence on the success rates and quantities of meat items produced. “Defectors” may therefore be punished for not contributing enough labor or work effort to production tasks, rather than for not producing a certain amount of food[10].

The existence of enforced norms to share and to produce eliminates the collective action or public goods problem of group food production decisions by transforming the payoff structure from that of a Prisoner’s Dilemma into that of a mutualism, whereby defection becomes an unviable option. Thus, producing food (sharing some, and receiving some when others produce food) has greater payoffs than relying on your own solitary food production. Hunting is a viable provisioning strategy, even though mens’ focus on game production may be motivated, in part, by the mating benefits that accrue from costly signaling (Bird 1999), especially given the subsistence decisions of women.

5. What is the value of reputation?

When asked why they often feel compelled to give away shares of production to others, many informants often report either a group-oriented reinforcement-type response such as ‘that is our custom’, or a sanction-avoidance response such as ‘If I don’t give, others will be angry, or say I am stingy’. These responses highlight the information-value of sharing, where giving may be a useful means of advertising a reputation for wealth or ability, generosity, or merely a lack of stinginess.[11] If producers lack control over distributions of certain resources, then their desire to pursue those resources (especially when net benefits are less than those from alternative foraging strategies) may reflect a costly signal. However, even with strong producer control, decisions to give widely may be guided by a desire to signal some attribute. Signals are easily interpretable by a large audience when repetitive, stereotyped, and conspicuous (Krebs & Dawkins 1984; Johnstone 1997). Giving significant portions of packages away to many other individuals is a ripe opportunity to gain abundant status points. Game animals are usually the most culturally valued, due perhaps to the difficulty in acquiring them and their high nutrient density; these items are typically the most widely shared of all food resources. Good hunters are therefore usually accorded much prestige. Good hunting ability is accorded high status among the Siriono (Holmberg 1969), Ache (Clastres 1972), Gunwinggu (Altman 1987), Yuqui (Stearman 1989), Dobe !Kung (Lee 1972), Nyae Nyae !Kung (Marshall 1976), Copper Eskimo (Damas 1972), Agta (Griffin 1984), G/wi (Silberbauer 1981), Pilaga (Henry 1951), Andamanese (Radcliffe-Brown 1922), and presumably others not mentioned here (cf. Wiessner 1996).

Although Dowling (1968) recognized over thirty years ago that imbalances in production and distribution are often corrected through “a counterflow of esteem and influence to the person who contributes the most" (505), no study has ever measured whether the tangible benefits that arise from such esteem outweigh the costs of giving. The fact that the highest producers among the Ache, Pilaga, Hiwi, and Yuqui consistently gave away more than they received compared to their poor producing counterparts (Gurven et al. 2000b; Henry 1941; Gurven et al. 2000a; Stearman 1989) suggests that the pursuit of esteem is worthwhile (especially because producer control is evident in these groups), but that we still have little understanding of the appropriate return-benefit currencies. Successful Meriam hunters have higher age-specific reproductive success, higher quality mates, and more sexual partners than poor hunters (Smith et al. n.d.). Ache women are more likely to report good hunters as extramarital lovers than poor hunters (Hill & Kaplan 1988), and children of good hunters exhibit higher survivorship than those of poor hunters (Hill & Hurtado 1996). Additionally, Ache that give relatively high proportions of their production away to others are more likely to receive food assistance during periods of sickness and injury which inhibit production activities (Gurven et al. 2000b). That high producers or generous individuals receive return benefits due to the prestige of giving runs counter to the idea that leveling mechanisms (see above) exist to prevent the accumulation of benefits. However, additional mating benefits, assistance to spouses (increasing spouse fertility), increases in offspring survivorship, and social insurance are substantial benefits that need not disrupt a loosely egalitarian social structure.

CS theory may shed insight into numerous observations of apparently ‘useless’ sharing. Hiwi women often give roots to women who already have their own roots, so that after sharing is done, none have more than they did prior to sharing (Gurven et al. 2000a). Chácobo women and men give each other manioc flour and fish, respectively, in the same manner (Prost 1980). The Batek do the same for a variety of foods (Endicott 1988), the Mbuti do the same with honey (Ichikawa 1981:65), and the Agta do the same with betel nut chews (Griffin 1984). The Western Desert Aborigines have “evolved a system that compels people to share food, even when such sharing might not be strictly necessary, in order to assure that when an emergency arises…the relationships that require sharing between kin are strong” (Gould 1981:435). These anecdotes support the notion that the act of sharing has communication value, perhaps independent of the items being shared (Bird-David 1992). These acts of sharing may signal an intent to engage in reciprocal cooperative endeavors, rather than a phenotypic quality of the acquirer. However, redundant sharing as described here may be due to the small cost of giving, when food is locally abundant but not easily storable. This kind of giving may act as a “raising-the-stakes” strategy (Roberts & Sherratt 1998), useful for building trust and identifying generous, dependable individuals for engaging in future cooperative relationships[12].

6. What about women’s sharing?

The few quantitative studies which examine both male and female production and distribution patterns suggest that women do not collect food only for the purpose of household provisioning. Ache and Hiwi women share all foraged plant foods extensively, giving away about 55% of all collected food in both cases. Among the Hiwi and Ache (on forest treks and at reservation), there are no sex differences in sharing behavior after controlling for the package size of the resources they acquire. A similar pattern is described among the Agta, where wild plants and cultigens are shared in the same manner as meat, and where women intentionally harvest an abundance of roots for the purpose of sharing (Griffin 1984). Both men’s and women’s sharing increases with larger package sizes, suggesting that men’s sharing patterns are not unique. Most importantly, Ache, Hiwi, and Agta women generally return to camp carrying packages of palm fiber or roots larger than their family members can consume, and widely share these packages with individuals outside their nuclear family. Any gathered food or cultigen comes in small increments and so production levels are subject to an acquirer’s control. Any woman could stop working whenever she had enough food for her family. These women must therefore overproduce collected foods intentionally because they gain some benefit from the food they transfer to others. Unlike the classic payoffs to males assumed in 'showoff' and most costly signaling models, the gains from sharing by women cannot be increased number of mating partners. Instead, the gains from sharing must be in some form that impact women or their offspring.

If women’s sharing benefits offspring, then men’s similar sharing patterns may very likely also benefit offspring. The fact that only men choose the variance-prone foraging strategy of hunting cross-culturally, while women focus their subsistence efforts on predictable gathered foods, may provide support for the notion that men are more likely to be motivated by CS than are women. However, alternative explanations are also likely. In general, a sexual division of labor is expected when multiple currencies (e.g. protein-lipid, carbohydrate) provide utility, when the activities that produce them are mutually exclusive, when either sex has a comparative advantage, and when high productivity requires a relatively long training period. Under these conditions, specialization is so efficient as to be inevitable (Becker 1991).

7. Multiple currencies and multivariate analyses

An individual can give away shares to benefit kin, to receive like shares in the future, to avoid high defense costs, and/or to receive some other fitness-enhancing benefit either at the time of distribution or on a future occasion. Evaluating the relative impact of different payoffs on the variation in sharing behavior across individuals within a population, or even within individuals over time, will require a systematic way of comparing the expected magnitudes of benefits associated with each hypothesized motive for food transfer. A KS component would include the net boost of food on the reproductive value of kin. A RA component would include the expected time-discounted return benefits of receiving either like food resources or other fitness-enhancing items or services. A CS component would require estimates of the fitness value of having established one's 'high quality' to the audience composed of witnesses to the high production (and redistribution) activities. It is important to recognize that giving a certain amount of some food resource is expected when the sum of these time-discounted benefits outweighs the present costs of giving. This means that the different payoffs can all contribute to the final decision to share food. If an individual shares food when the sum of these benefits is less than the immediate costs of giving, then we may conclude that TS or some other explanation accounts for the behavior.

The overlapping predictions of sharing models require sharing analyses to incorporate multiple influences simultaneously, rather than examinations of single variables on sharing outcomes. However, detailed multivariate analyses of factors associated with different levels of sharing have been published for only two groups: the Hiwi of Venezuela (Gurven et al. 2000a) and the Ache of Paraguay (Gurven et al. 2001; 2002). At the time of study, the Hiwi population contained 37 nuclear families (106 individuals) and were living at a permanent settlement, with wild foods composing 95% of the diet. The Ache reservation sample contained 25 nuclear families (121 individuals) and was also based at a permanent settlement, with farm foods providing the majority of the daily caloric intake, in addition to traditional forest foods. The Ache forest sample consists of four two-week treks by bands that contained 10 to 14 families (17 to 48 individuals), and where wild foods composed over 95% of the daily diet. Multivariate analyses focused on two questions: 1) What affects the percentage of food production given to other families? 2) What affects how much a specified family A gives to a specified family B over the sample period?

FIGURE 2a. What determines how much a Hiwi acquirer gives to other nuclear families?

Figures 2ab show the results of path analyses meant to answer these two questions for the Hiwi[13]. As mentioned previously, the Hiwi results indicate that donor sex and age have no impact on giving when other relevant variables are included in the same analysis. Resource package size and a measure of resource acquisition “variance” have strong separate positive impacts on sharing depth, while the number of individuals in the donor family has a negative impact on the percentage of food given to other families (Figure 2a). Large, risky resources are shared with greater breadth than smaller, predictable resources, and small families give more away than large families. The size of a recipient nuclear family and the percentage that family gave to a donor family each have strong, positive independent effects on the percentage of food the donor family gave to that recipient family (Figure 2b). Thus, contingency and recipient need are significant predictors of sharing depth even when controlling for kinship and spatial proximity of households. The multivariate analysis also suggests that the positive effect of kinship on giving may be an artifact of residential distance, which acts as a stronger predictor of giving than kinship. One interpretation of this kinship and distance relationship is that close kin who desire to share with each other according to RA choose to live within close proximity to each other, as suggested by the correlation, r=0.5, between kinship and proximity.

FIGURE 2b. What affects how much Hiwi family A gives to family B?

Multivariate analyses of sharing among Ache during temporary foraging treks and at the reservation settlement have found similar effects of donor family size and resource package size on the percentage given to other nuclear families (Gurven et al. 2002). Additionally, the number of individuals present on trek was positively associated, and the total daily food production of a specific resource type was negatively associated, with the percentage of that resource type given away to other families on foraging treks, consistent with both TS and RA. In both forest and village settings, a significantly larger percentage of meat resources was given away compared to other resource types, even after controlling for the size of those resource packages. Distances between households and their relative visibilities were strong predictors of the total quantities of food exchanged among specific families in both Ache settings. Two important differences found when comparing forest and village contexts are noteworthy: kinship and contingency have little effect on receipt of meat in the forest, while these variables exhibit strong effects at the reservation. However, kinship and contingency are strongly correlated with increased giving of non-meat items among pairs of families during foraging treks, suggesting that much of the variation in inter-household sharing patterns across settlement and forest may be due to differences in the production systems that produce different kinds of foods, rather than any magical qualities associated with meat.

8. Production and distribution: food versus work effort

Two general patterns of sharing are apparent from the review presented above: high sharing depth and breadth with little to no contingency between giving and receiving, and restricted sharing depth and breadth with significant contingency. These patterns represent the two extremes of a continuous range of sharing patterns. The most important ecological feature which impacts the costs and benefits to giving is the suite of profitable resources available as preferred foods as a function of extraction technology, cultural knowledge, and the social relationships that negotiate the relationship between food production and distribution. This relationship is probably responsible for much cross-cultural variation in transfer patterns. While group size and spatial distribution of individuals, which act as proximate influences on sharing, are also important, these variables probably derive from the production system.

8.1 Resource ecology. The degree to which the diet is composed of large, asynchronously acquired foods should affect overall breadth and depth of sharing because under these conditions, others’ level of need is high while costs of sharing to a donor are relatively small. The two extremes are exemplified by diets consisting primarily of difficult-to-acquire bulky meat packages which arrive intermittently to camps, as in assertive egalitarian groups, and those consisting primarily of small, predictable, relatively easy-to-harvest carbohydrates bundles, as in forager-agriculturalist groups. Predictable, cultivated and gathered food items are shared with less depth and breadth than meat items in all societies where this has been investigated, including the Ache (Kaplan & Hill 1985; Gurven et al. 2001), Hiwi (Gurven et al. 2000), Yanomamo (Hames 1990), !Kung (Lee 1979), Hadza (Hawkes et al. 2002). While meat items tend to come in larger packages than non-meat items, and resource package size correlates strongly with increased sharing depth and breadth, meat items are still shared more widely among Ache, Hiwi, and Yanomamo when controlling for differences in resource package size. Much variation in cultural-specific sharing depth and breadth is partly a function of the variation in diet composition among groups. Risk-reduction, TS, and CS, however, cannot explain why these characteristically “unrisky” food items are shared at all, yet transfer of these foods is substantial.

8.2. Food production. The diets encountered among different groups should not be viewed as extrinsic characteristics of those groups. Indeed, the four evolutionary models discussed in this paper (KS, RA, TS, and CS) ignore most characteristics of the production system that generate food items found in the diet. The only aspect of production addressed by these models is the degree of acquisition variance based on luck. Production will depend on the kinds of high caloric return resources available in the local environment, the available extraction technology and knowledge required to convert “resources” into food, and the social arrangements necessary to achieve coordinated production (Alvard and Nolin 2002). If a food item produced by a solitary individual is shared differently than a jointly-produced item, especially when multiple individuals are critical to the production process, then group-oriented production processes contribute an additional motivation for food transfers. Empirical studies of cooperative foraging decisions and distribution patterns suggest that producing and receiving are closely related and that focusing on one without the other misses an important component of social and economic behavior (Hawkes 1993; Hill & Kaplan 1993; Frank 1985; Sosis in press; Hill 2002). If substantial portions of certain resources are routinely given to others and little is given back in return, then the expected net caloric return rate for personal consumption may be low, so that widely distributed foods should drop out of the optimal diet. Similarly, items which reduce the long-term average caloric return rate may be pursued if the use value of those items (through trade, group production, signaling information, body adornment, etc.) inflates their worth.

Pro-social foraging behavior, by definition, requires that individuals associate in groups. The degree to which groups of individuals share together may be related to the degree to which they forage together. The extent to which production relates to distribution should reflect the degree of coordination and/or specialization in the production process. Indeed, group production varies in the extent to which it should be labeled cooperative. Three possibilities for group production include: a) simultaneous solitary foraging, where the presence of other individuals has little effect on personal production, b) mutualism, where group cooperation is compatible with each cooperator’s individual interests (i.e., no temptation to defect), and c) prisoner’s dilemma or public goods-based cooperation, where group interests conflict with benefits that can accrue to defecting individuals. Simultaneous solitary foraging seems to describe group hunts by Gombe chimpanzees (Boesch & Boesch-Achermann 2000), whereas mutualism seems to describe group hunts by Tai chimpanzees (ibid), social carnivores such as African wild dogs and Serengeti lions (Dugatkin 1997), fishing among the Ifaluk (Sosis 1998) and whaling among the Lamalera (Alvard and Nolin 2002).

To the extent that all individuals on group hunts increase their daily per capita intake through a combination of an increased prey encounter rate, decreased search costs, or an increased probability of pursuit success, relative to that from solitary hunting, human hunting may be labeled as mutualistic. For group hunts, and solitary hunts where band members pool the catch at the end of the day, all members may still gain mutualistic benefits. However, it is more likely that some individuals fare better than others by either engaging in any particular group hunt, or in the decision to pool kills at the end of any particular day of solitary hunting. Over a time span of days, months, or even years, however, those same individuals who could have fared better after a single event, are likely to gain net benefits if they receive food during times when they acquire little to none. Thus, it has been argued that the ability to reap gains from cooperation via reciprocity, as opposed to mutualism, depends on species-typical rates of discounting the future (Clements & Stephens 1995).

The few long-term data on individual hunting return rates among Ache and Efe men indicate consistent differences in hunting success and caloric efficiency over time (Hill et al. 1987; Bailey 1991). Whether or not high producing individuals gain net insurance benefits from sharing, or from any other status-derived benefit is an empirical question that requires a better understanding of how different feeding regimes affect long-term survival and fertility (Gurven et al. 2000b). It may, however, be the case that the costs of sharing are not paid back on average to high producers. In modern societies, many individuals pay years of auto, life, health and homeowner’s insurance premiums and never make any substantial claims that outweigh the summed premium costs. In general, these are wealthier individuals that can more easily afford the luxury of insurance coverage and that want to avoid the risk of catastrophe. This is consistent with the observation that the highest producers in foraging societies are the ones most likely to give away more than they receive (see above). Norms of giving enforced by sanctions as a means of punishing stinginess can “force” high producers to pay graduated income taxes. In this respect, giving may be regarded as a form of TS where the cost of not giving is a verbal or cultural sanction, especially when the number of high producers is small relative to the number of average to low producers. However, norms of sharing that benefit older individuals (at the expense of young high producers) will benefit those young individuals later in life when their dependency is relatively high. This is the same social convention that has led to social security programs in modern state societies, and so perhaps it is not surprising that it emerges amongst foragers as well.

Although contingent sharing of specific quantities of food may not exist in several egalitarian societies, contingency of a different form may be more appropriate in groups where individuals coordinate various subsistence-related tasks for mutual benefit. Where random, uncontrollable factors contribute a significant portion of the within-individual variation in production returns, maximum group production requires a sufficient number of person-hours invested in food obtaining activities. If food is pooled equally among group members, then maximizing per capita production is equivalent to maximizing group production. A contingency system may evolve which therefore rewards work effort rather than actual returns. Continued work effort requires the kinds of sanctions against laziness mentioned above, even if producer control is lacking and sharing is an automatic outcome of resource characteristics and recipient demand. In commenting on the work contributions expected from visiting Aka, Bahuchet (1990) reports that “if one stays longer [in the group] it is also necessary for him to participate in production activities” (41). The roots of equity and fairness considerations in such economies may be based on effort and time investment rather than on strict outcomes. When random factors significantly affect production, effort and output may not be correlated. Controlling for individual ability, the number of hours per day Ache men spent hunting had no effect on daily returns, and there was no quantity-based contingency for game sharing. However, in economies with more predictable diets, effort and output are more highly correlated and contingency based on output is more likely (especially when effort is more difficult to monitor). Thus, among the Hiwi, men’s work effort was highly correlated with daily hunting returns, and the contingency of meat sharing was strong.

This view suggests that time, labor contributions, and intent are important indications of commitment, and may reflect the social contract that defines the redistribution characteristic of many small communities. As discussed earlier, there are many ethnographic examples of hunters pooling catches among themselves in a first wave of sharing, consistent with the notion that “work transforms material things into property” (Barnard & Woodburn 1988). The Mbuti (Bahuchet 1990), Aka (Kitanishi 1998), Washo (Price 1975), Hiwi (Gurven et al. 2000a), Pintupi (Myers 1988), Northwest California Indians (Gould 1981), Netsilik Eskimo (Damas 1972), Lamalera (Alvard and Nolin 2002), Nyae Nyae !Kung (Marshall 1976) and the Makah (Singleton 1998) each have sharing norms that encourage initial distributions to other hunters who participated in the hunt. For example, cooperative hunts of hare wallabies and hill kangaroos among Pintupi Aborigines traditionally resulted in portions distributed to “all who participated in the hunt” (Myers 1988). The Hiwi always share capybara amongst all members of the one or more canoes that coordinate their movements in the pursuit of these acquatic game (Hill pers comm). When Ache hunters execute day hunts from the reservation in pairs, they always share killed game with their hunting partner.[KH1] Bailey (1991) reports that following group hunts among the Efe Pygmies, initial game distributions are biased toward participating members in the hunt, and that portions are allocated according to the specific hunting task. Thus, the hunter who shoots the first arrow gets an average 36% (and the most highly prized liver), the owner of the dog who chased the prey gets 21%, and the hunter who shoots the second arrow gets only 9% by weight. While mutualistic payoffs might encourage participation in group hunts, these payoffs are only insured through rules of distribution that benefit participants.

When the hunting task group includes all men present in camp, task group sharing and residential group sharing may be indistinguishable. When residential groups are not much larger than the hunting task group, preferential sharing in the first wave may be evident, but subsequent sharing may result in all band members consuming similar meat portions. Additionally, if prestige accrues from distributing shares, then recipients of shares from initial distributions who later redistribute portions to other have-nots gain additional status. With large residential groups, task group-based sharing can lead to exclusions of a significant number of band members.[14]

8.3. Bandwide sharing The exceptions to production task group sharing are extreme band-wide distributions that occur whether or not other recipients were members of the hunting group, or even whether or not they hunted at all. This often occurs in the distribution of very large game (relative to the band size), as among the Gunwinggu (Altman 1987), Hadza (Hawkes et al. 2001), !Kung (Lee 1979) Ache (Kaplan & Hill 1985), Western Shoshone (Steward 1938) and Owens Valley Paiute (ibid). However, wide distributions of even small game items have been described for the Hadza and Batek. Among the Ache, large cooperatively acquired game was shared no differently than game acquired by solitary hunters (Kaplan & Hill 1985). As described earlier, some foraging bands maintain norms of widespread meat sharing, contingent on the contribution of some meaningful productive work that may benefit others. In these cases, the cooperative unit is not the hunting task group, but the entire (or subset of the) band. Even if sharing is due to TS, if individuals who do not produce (and who are therefore not eligible to share) are ostracized or receive some form of punishment, then the resulting ‘reciprocal’ TS, where individuals take turns playing the role of acquirer and recipient but then share according to TS post-acquisition, is essentially identical to RA[15]. That sharing breadth and depth of most resources in small camps is similar to those in larger Ache foraging groups and the even larger setting of the village context, suggests that the widespread sharing patterns observed during Ache foraging treks and among other small-scale egalitarian groups is consistent with “strong” reciprocity (Gintis & Bowles 2000; Fehr & Schmidt 2000), even when the contingency of giving and receiving among pairs of individuals is not significant.

In these cases, we should instead find receipt of shares contingent upon time and effort spent in food production, or production-related work. A division of labor by sex, age, and skill enables individuals to specialize in activities for which they substitute at the highest return rate (Gurven & Kaplan n.d.). This division of labor rests on the assumption that members within a cooperative unit (be it nuclear family, a subset of the group, or the entire band) have access to the pooled food production. On extended foraging treks, 17% and 11% of Ache men’s and women’s foraging time were spent engaging in activities that was intended to increase others’ caloric production rates at the expense of their own (Hill 2002). For example, some individuals cut trails for others, carry game and other items for others, indicate resource locations for others to exploit, flush monkeys so others have a clear shot at them, call others to fresh spoor, and leave some resources such as honey and armadillos for others to pursue while they continue searching. This high degree of cooperation may explain why game is given to those who did not hunt, and why gathered and collected items are often shared outside the nuclear family (especially when harvesting involves economies of scale - Kaplan et al. 1990; Gurven et al. 2001).

8.4. Restricted sharing Many groups, however, do not engage in bandwide sharing of meat items, and instead restrict initial sharing to the task group or extended family, with only subsequent sharing to other group members. Future research should focus on understanding the conditions that favor these different norms of sharing. Inter-dependent subsistence, small group size (see below), high average relatedness to group members, coordination in residential structure, and outside threats, may all favor increased within-group sharing. Increases in group size, weak punishment against slackers, and shifts in diet towards smaller, more predictably acquired foods may instead promote more self-sufficiency (e.g. storage) at smaller levels of social organization (i.e. the nuclear family). Thus, among Northwest Coast Indians, Gould (1981:451) reports that “each family was able to collect, prepare, and store its own food resources largely by its own efforts” and that “all food was redistributed with the clear expectation of immediate repayment, either in labor or in prestige goods”. Moulton & Dunlay (1983:259) provide similar evidence with the Nez Perce of the Columbian River plateau.

9. Conclusion

Available cross-cultural evidence of production and distribution patterns among small-scale societies cannot rule out RA as a primary model of food transfer, while the relevance of TS in recent treatments seems overstated. The idealized conditions required for widespread TS may be rare cross-culturally. This suggests that the delayed benefits from hunting need to be included when considering whether hunting is a viable subsistence strategy. Few explorations of these returns have been done systematically. While most investigations examine simple tit-for-tat reciprocity, more complicated social arrangements, including those where important social support is provided only if one adheres to socially negotiated sharing norms, seem more appropriate. While mens’ focus on game production may be motivated, in part, by the mating benefits of signaling, hunting seems to be a viable provisioning strategy, given the subsistence decisions of women[16].

Despite the compulsory nature of giving in small-scale societies, patterns of giving and receiving are sensitive to costs and benefits affected by the types and sizes of foods being shared, others’ labor contributions to the food’s production, and other bargaining arrangements. The weighting of fitness benefits and costs yields the conditions of giving from an “ultimate” gene’s eye-view. However, individuals may give for reasons that seem contradictory with one or all of the genetic sub-components, if based on proximate psychological and emotional motivations invoked under different or novel circumstances, or if based on adherence to group-level norms or heuristics that differentially benefit certain individuals. Some of the difficulties in understanding sharing behavior stem from a confounding of the levels of analysis: proximate motivations, cultural pro-social norms which partially correlate with actual behavior, and outcomes in terms of genetic fitness. While all behavior influenced by natural selection must, by definition, be explicable in terms of differential genetic replication in an ancestrally relevant environment, the link from individual behavior to genetic selfishness need not be straightforward. Altruistic, pro-social, and self-interested behavior at the individual level may all be consistent with genetic selfishness. Revisionist theories in psychology (Caporael et al. 1989) and economics (Bolton 1991; Rabin 1993) have recently been developed to incorporate principles of equity, fairness, or others’ utility into personal utility functions, in an attempt to explain why human subjects in various experiments act pro-social when the extrinsic conditions of these experiments predict widespread defection. These models may help us understand how individuals make cooperative decisions at a proximate level, but the reason why any specific utility function supports empirical findings will require an ultimate-level explanation that links evolved psychology or heuristics to fitness in a specific environment. For example, while signaling generosity is costly in the short-term, long-term benefits may accrue in societies where there are frequent opportunities for cooperative gain, when payoffs to cooperation at these opportunities are substantial, and when the choice of cooperative partners is based on observations of past generosity. Preliminary results of economic games designed to measure propensities for generosity in many traditional societies support this view (Henrich et al. in press).

Rather than assuming any universal tendencies for humans to cooperate extensively in all ancestral-like contexts, human behavioral ecology has been successful in sparking systematic inquiry into the whys and wherefores of costly giving. By linking the transaction of giving with long-term insurance benefits, reputational investments, and mating interests of male and female actors, behavioral ecology has generated abundant useful predictions that when tested in many societies should greatly increase our understanding of human social behavior. However, there are still many gaps in our understanding of why individuals give differently within and among groups. In particular, future work should help bridge cognitive and psychological motivations, actual outcomes, long-term consequences of behavioral dispositions and behaviors on fertility and survivorship, short-term and long-term costs of withholding food, aspects of sharing that constitute strong signals, and the mechanics of multi-person negotiations in effecting appropriate enforceable social sharing norms. More long-term research is also needed to bridge our understanding of short-term reciprocal altruism and the kinds of long-term reciprocity that tend to reflect cultural emphases on lifelong balances. Finally, more multivariate quantitative analyses combined with detailed ethnographic descriptions of social norms, violations, and perceptions of fairness and equity can reveal much insight into human cooperation.

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Figure Legends

FIGURE 1. Edgeworth Box of Food Exchange

FIGURE 2a. What determines how much a Hiwi acquirer gives to other nuclear families?

FIGURE 2b. What affects how much Hiwi family A gives to family B?

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[1]I use the terms ‘transfer’ and ‘sharing’ interchangeably even though sharing implies intentionality and active giving, whereas transfer is a more neutral description. Anthropological ethnographies rarely distinguish between the two usages.

[2] 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 1996).

[3] 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 have-nots) (Rogers 1993) since the former yields a greater inclusive fitness benefit to the donor.

[4] 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, while others helping the sick producer recover may be viewed as a form of byproduct mutualism (Dugatkin 1997).

[5] While computer simulations reveal that significant correlations between individuals in amounts given and received are possible when TT is the sole cause of food sharing, correlations greater than 0.2 were only found in highly structured groups of few individuals.

[6] 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.

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

[8] Due to the format of the data available for the Pilaga, I estimated contingency as the correlation between the % of family A’s consumption (above A’s own contribution) provided by family B and the % of B’s consumption (above B’s own contribution) provided by A.

[9] Correlations of general contingency are similar in magnitude to those of specific contingency, although 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).

[10] Existing game theoretical work on producer, scrounger, and opportunistic forager strategies reveal that all three strategies can co-exist in the same population (Vickery et al. 1991). Defectors or “scroungers” do not proliferate when producers can maintain control over a sufficient portion of their kills (the producer priority discussed above), 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.

[11] 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 and Weskema 1991).

[12] 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.

[13] Path analysis is a useful tool for examining the separate effects of multiple, often co-dependent 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.

[14] When residential bands increase in size due to non-foraging related benefits of grouping (e.g. mating opportunities, proximity to missions or nearby towns, defense against hostile neighbors, etc.), traditional group fissions like those mentioned above for the Yanomamo, Ache and the Penan are unlikely, and thus more restricted sharing networks, and more stringent contingency can result. As Prost (1980) 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” (63). 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.

[15] That the same meat items are shared contingently in the village setting, but with little or no contingency in the forest foraging context urges us to rethink the potential role of RA, TS, and CS in small-scale egalitarian cultures. In the smallest foraging groups, RA may be indistinguishable from TS and some forms of CS, even if a contingency correlation is found to exist (Gurven n.d.).

[16] 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.

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[KH1]If you think that you saw this yourself, you don’t need to cite me.