This drive to be a member of a group or tribe, however, goes beyond simple defense strategy or strength in numbers. We will sometimes make choices that benefit others, even at our own expense, and we share this tendency, the tendency to be generous, with our closest animal relatives. In one experiment, researchers taught monkeys to pull a chain in order to get food. Then they changed the setup so that when a monkey pulled the chain, the machine gave the animal some food but also delivered an electric shock to another monkey. Most of the monkeys stopped pulling the chain. Some starved
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