WHY MEN Kill

Robert puts the Polaroid of Robert at the top of the layout. Hie is doing something more commonly associated with camping mattresses and life jackets: in Patton's words, he's self-inflating. What Patton means is that Robert has placed his Polaroid considerably higher in the warrior hierarchy than his exploits or reputation would merit. Robert thinks he's boss of the beach. This is the kind of guy you want to watch out for. A man at the bottom of the heap has the most to gain and the least to lose. He's more likely to make a rash grab for power. He's also more likely to lose should the conflict turn violent. Which is where good bluffing tactics come in.

Richard Wrangham, a Harvard primatologist who helped formulate current ideas about violence in human evolution, has a theory called military incompetence. It explains why a man like Robert would blunder forth into battle when any fool can see the odds are stacked against him. Evolution should have put a stop to this sort of behavior, but it hasn't. Wrangham and Patton argue that self-deceit facilitates it. A strong bluff can deter an enemy, even an enemy which most likely win. And the most effective bluffers are the ones who don't think: they're bluffing. It's possible to elevate your status and enjoy the perks of being a mighty warrior without even going into battle. Eventually your number is bound to come up, but in the meantime you've sired a pack of bluffers to carry, on the trait.

So it is that ultimately suicidal violent traits can turn out: to be evolutionarily successful. Take the case of despots and dictators. Here are men who live with enormous risks every day of their lives. When the risk-taking pays off, it pays off big.

"Remember that the despotic individual is really only a vehicle for the trait," says Patton. "Let's say we have 10 individuals with the psychology to be despotic. Nine get wiped out; they push it too far. One of them succeeds and gets 20 wives. Overall, it's still a good reproductive payout." Patton cites the example of a man from Conambo named Basilio, whose grandfather was a warrior of wide repute. Eventually someone killed him, but in the interim he amassed ten wives and several dozen children. "The salmon who stays out at sea instead of struggling upstream may live a long life," says Patton, "but he doesn't reproduce. From an evolutionary perspective, he might as well be dead."

Two women are ladling chicha from a vast ceramic urn. Patton wipes termites off his pants leg and leans hack against the porch: "It's Miller time!" Robert's daughter sets down a plate of yams the color of Barney. We eat nine. When steamed tapir fetus may be waiting around the bend, you make the most of purple yams.

Late one evening, we are sitting on the schoolhouse veranda, watching moths suck minerals from a sweat-infused T-shirt that hangs on the line. A man appears out of the darkness and speaks to Patton in hushed, urgent tones. A woman named Suitiar has fallen ill on the trail near the house of a man named Kaiyashi. The suddenness and severity of the illness has led her family to suspect witchcraft, and a shaman--the man we saw earlier today carrying a shotgun--is about to perform a ritual to remove a tsentsak, a supernatural psychic dart blown by another shaman, often at someone else's behest. As a backup, they want Patton there, with his bag of Western pills and ointments. And so we make our way to Kaiyashi's house on the far side of the river. It's rush hour in the jungle. Leaf-cutting ants cross the airstrip in columns six inches wide. Frogs make sounds that are way too big for them. Overhead, shooting stars and fireflies flash, and it's sometimes hard to tell which is which.