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Social scientists believe they know why America has become so divided along political lines. “The human brain in many circumstances is more suited to tribalism and conflict than to civility and reasoned debate,” The Wall Street Journal reported last month in a piece headlined “Why Tribalism Took Over Our Politics.”

Modern communication tools are especially able to exploit this finding, providing users with what they want to hear rather than challenging assumptions. “Decades of social science research show that our need for collective belonging is forceful enough to reshape how we view facts and affect our voting decisions,” the essay asserts. “When our group is threatened, we rise to its defense.”