Experimental tests of the tolerated theft and risk-reduction theories of resource exchange.

Here we report the results of an experiment that tests the reciprocal risk reduction and 'tolerated theft' or taking hypotheses for why the human species is unique in having extensive exchange of resources among non-kin. We designed an experiment to determine whether, in response to variance of resource acquisition, people exchange food resources via taking or, alternatively, form reciprocal relationships based on giving. In the experiment, subjects forage individually, experience variation in resource acquisition, and then consume either by actions in which resources are taken from, or moved to, others in a group environment. The key feature of the experimental design is that individuals can transfer resources to others, attempt to take resources from others and defend against take-away attempts. Many subjects begin by attempting to take resources from others, who can resist those attempts at a cost to each. Over time, subjects shift to a cooperative strategy of voluntary reciprocal giving, a response not suggested by the instructions. These results provide evidence that people are independently able to overcome initial use of taking strategies, evaluate gains from exchange, and create endogenous reciprocal trading relationships as a response to unsynchronized variance in resource availability.