Researchers created a box divided by a clear plastic partition — a pool of water on one side and a dry platform on the other. They then threw a piece of chocolate into the mix, to test if a rat's altruism was greater than his sweet tooth.

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Jim Festante is an actor/writer in Los Angeles and regular video contributor to Slate. He's the author of the Image Comics miniseries The End Times of Bram and Ben.

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