Shoppers crowd a narrow street outside Tsukiji market in Tokyo on Dec. 31, 2010. Japan has relatively tight social rules. And that makes sense, according to researchers. When people are squeezed together, they have an incentive to cooperate.
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Smoke billows from the Jabal Mohsen community while a Sunni gunman takes cover behind a wall in the Bab al-Tabbaneh neighborhood during clashes in Tripoli, Lebanon, on July 9, 2008.
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Elizabeth Warren, assistant to the president and special adviser to the Treasury secretary on the Consumer Financial Protection Bureau, testifies before a House Oversight Committee hearing on Tuesday.
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