The human capacity for cooperation is at the root of many of the most impressive accomplishments of our species—from the evolution of language and tool use to the construction of pyramids and space stations. Although some forms of cooperation are motivated by self-interest or fear of punishment, the forms of cooperation that are most likely to succeed in the face of personal costs stem from love of the group. In this article, I consider one of the most intense forms of ingroup love known to psychology—identity fusion—resulting from shared suffering, from the battlefield and football pitch to the hospital ward and prison camp. Though often harnessed in ways that fuel intergroup conflict and violent extremism, fusion can just as easily be channeled into peaceful and consensual forms of prosocial action, for example, to tackle climate change, reduce crime, prevent intergroup conflict, or respond to pandemics. Understanding and applying the insights generated by research on fusion can help policy makers foster more effective forms of cooperation for the public good.



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