There are many reasons to be nervous in the village of Conambo in the Ecuadoran Amazon. You can be nervous about crossing a large swift river in a tiny wobbling canoe. You can be nervous about the sand flies that carry Leishmania parasites, which bore through your sinuses and eat out your brain. You can be nervous about the giardia in the manioc beer that can wreak havoc with your bowels, the tarantula in the outhouse, the vampire bats in the schoolhouse.
The Achuar people of Conambo are not especially nervous about any of these things. The Achuar are nervous about the Achuar. The Achuar hold the dubious distinction of having had, in The Achuar Indians of Ecuador have, by one count, in recent generations, one of the highest murder rates on Earth. In 1993 a poll of villagers revealed that 50 percent of their immediate male ancestors had died from shotgun blasts. (The traditional Achuar greeting is Pujamik—“Are you living?”)
If you weren’t born here, you for damn sure wouldn’t live here. Unless you were John Q. Patton. Patton, an anthropologist at the University of Colorado and the Center for Evolutionary Psychology at the University of California at Santa Barbara, studies the roots of war and killing. He takes a biological approach to human behavior, which is to say he expects Darwinian theory to explain it. And from that evolutionary perspective, war is something of a problem, because it appears to be an altruistic act: you are risking your life for the good of the communit...