The true source of the tragedy of the human condition is that we evolved in conditions of intense resource competition. Like Russell Crowe organizing the outnumbered combatants in Gladiator, natural selection favored individuals who cooperated to avoid being killed—and, if necessary, to kill. Regrettably, Einstein's concise question, “Why war?”, is answered by nature equally succinctly: because we are human.

Dominic Johnson is Professor in the Department of Politics and International Relations, University of Oxford. Bradley A. Thayer is Professor and Head of the Department of Political Science, Utah State University.

Image: Wikimedia Commons.

Editor's Note: This piece was originally posted on January 29, 2013. We are recircualting it due to audience interest.