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Food Sharing on Ifaluk

by LAURA L. BETZIG and PAUL W. TURKE Museum of ZoologylDepartment of Anthropology, University of Michigan, Ann Arbor, Mich. 48109, U.S.A. 26 III 86 Food sharing is probably universal in human societies (e.g., Sahlins 1972); it has also recently been considered a new Rubicon in human evolution (e.g., Isaacs 1978). So far, little quantitative work has been done to determine how and why people share food (but see Kaplan et al. 1984, Kaplan and Hill 1985, Betzig n.d.). The analysis which follows uses quantitative data to determine whether or not food sharing on Ifaluk, a Western Caroline Island, is an adaptive activity. Hamilton (1963, 1964) predicted that apparent altruism will be adaptive where k > 1/r, where k represents the ratio of reproductive benefit o the recipient o reproductive cost to the donor and r is the proportion of shared genes identical by descent. Gifts reciprocated in kind may be adaptive as well (e.g., Trivers 1971), but, because a return in kind on any gift is never a certainty, actors may be expected to minimize the risk of loss, other things being equal, by investing in related individuals (e.g., Essock-Vitale and McGuire 1980, 1985). Other things which may not be equal include the ability of the recipient to benefit by the gift, the cost of giving it, and, possibly, the cost of not giving it (e.g., Moore 1984, Blurton Jones 1984; see also Feinman 1979). In predicting that people will satisfy Hamilton's inequality in their food-sharing activity we make three assumptions. First, close kin should have been available as sources of altruism throughout human evolutionary history. The ethnographic record, especially on hunting-and-gathering societies (e.g., Lee and DeVore 1968), strongly suggests that this has been the case. Second, shared food must currently and/or historically have contributed to recipients' fitness. Both comparative (e.g., Betzig 1986) and quantitative (e.g., Irons 1979, Boone n.d., Borgerhoff Mulder n.d.) data from traditional cultures, including Ifaluk itself (Turke and Betzig 1985), suggest that access to productive resources corresponds to reproductive success. Third, reproductive costs and benefits not taken into account must roughly average out. Our analysis suggests that food sharing on Ifaluk does take place among close genealogical kin and that individuals do take specified costs and benefits into account, including the cost of transporting a gift of food, the cost of not giving food to people of rank, and the benefit of giving food to households with a higher proportion of dependent children.