Do genes make us do it? The idea that human behavior is driven by genes makes many people uncomfortable, and nowhere is the dispute more bitter than when discussing the biological underpinnings of violence.
The war of ideas over violence and human nature has raged since the 1600s, when philosopher Thomas Hobbes first speculated that the "natural condition of mankind" was one of violence and conflict. In the 1700s, Jean-Jacques Rousseau saw things differently. Enthralled with accounts of the New World, he argued that civilization, not nature, shaped the human propensity for violence.
Social scientists have spent the last three centuries embroiled in debate over the degree to which human nature and culture are responsible for war.
In recent decades, biology has entered the fray. Since Jane Goodall first documented the disturbing reality that chimpanzee communities engage in lethal raids against other chimpanzees, evidence has been mounting in support of biological explanations for our species' capacity for warfare. Over the last few years, scientists have converged on something of a consensus: The human propensity for lethal violence against "out-group" members has deep evolutionary roots.