Reciprocal food sharing

Evolutionary biologists have developed various theoretical models to explain the evolution of food-sharing behavior—"the unresisted transfer of food from one food-motivated individual to another"—among humans and other animals.

Models of food-sharing are based upon general evolutionary theory. When applied to human behavior, these models are considered a branch of human behavioral ecology. Several types of food-sharing models have been developed, including kin selection, reciprocal altruism, tolerated theft, group cooperation, and costly signaling. Kin selection and reciprocal altruism models of food-sharing are based upon evolutionary concepts of kin selection and altruism. Since the theoretical basis of these models is formulated around reproductive fitness, one underlying assumption of these models is that greater resource accumulation increases reproductive fitness. Food-sharing has been theorized as an important development in early human evolution.

W. D. Hamilton was among the first to propose an explanation for natural selection of altruistic behaviors among related individuals. According to his model, natural selection will favor altruistic behavior towards kin when the benefit (as a contributing factor to reproductive fitness) towards the recipient (scaled based upon Wright's coefficient of genetic relatedness between donor and recipient) outweighs the cost of giving. In other words, kin-selection implies that food will be given when there is a great benefit to the recipient with low cost to the donor. An example of this would be sharing food among kin during a period of surplus. The implications of kin-selection is that natural selection will also favor the development of ways of determining kin from non-kin and close kin from distant kin. When Hamilton's rule is applied to food-sharing behavior, a simple expectation of the model is that close kin should receive food shares either more frequently or in larger quantities than distant relatives and non-kin. Additionally, greater imbalances in the quantities shared between close kin are expected than those shared with non-kin or distantly related individuals However, if reciprocal altruism is an important factor, then this may not be the case among close kin who are also reciprocity partners (see subsection below). Based on Feinman's extension of Hamilton's model, cheating such as recipients not sharing food with their donors, is more likely to take place between unrelated (or distantly related) individuals than closely related individuals.

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