Decades ago, when I was a bright-eyed undergraduate student, I saw a documentary called "Dead Birds" in my cultural anthropology class about the Dani of New Guinea, and it changed my life.

Brought up in a nice, middle-class, white American family, I had no idea that there were people in the world who still lived in huts, kept pigs, and spent their days on high, swaying platforms looking for the enemy. And when the enemy came screaming over the hill, wearing elaborate feathered headdresses and carrying spears, I was stunned into becoming an anthropologist, right then and there.

For most of us, it is impossible to fathom the way many people around the world live. We don’t know that there are still plenty of hunters and gatherers, still people who make their living off small plots of the land, still people practicing the spiritual beliefs of their ancestors.

Globalization has reached far, but not that far.

Anthropologist Stephen Beckerman and his colleagues at Pennsylvania State University have reminded us of the power of learning about non-Western groups with their new research paper on the Waorani, the most murderous people on Earth, published this week in the journal Proceedings of the National Academy of Science.

Sure, the Waorani have been influenced by Western culture, and pacified by missionaries, but the results of their bellicose behavior are still with them.

At peaceful white contact in 1958, the Waorani were on the way to extinction at their own hand. They were down to 500 people because almost half the population, including men and women, had been killed by other Waorani. They were caught in a cycle of revenge that demanded not just an eye-for-an-eye but the complete elimination of the "enemy."

Taking the evolutionary view, other anthropologists had looked at warring behavior in another fierce Amazonian group, the Yanomamo, and decided that aggressive men who killed others ended up with more wives and children, so being a warrior was presumably a good strategy for passing on genes.

But interviewing older men who had participated in this lifestyle of homicide, Beckerman and colleagues found that Waorani warriors did worse in terms of reproductive success and their killing was for naught, in evolutionary terms.

These two studies of two different groups living in similar ecologies of the Amazonian forest underscore the continuing need to look and listen to groups around the world. Only from such comparisons can we see the variety of human behavior, and how we humans get ourselves into real trouble with our bad behavior.

Here, for example, we have revenge at its worse. In one group, the Yanomamo, the killings resulted in times of peace and love and more babies, and in the other, the Waorani, endless revenge was leading to the end.

Oddly enough, Beckerman's work also suggests that contact with white people may not have been such a bad thing for the Waorani if it saved them from themselves.

But perhaps that's just a white, middle-class Western view of life, one that comes from watching others and not being them. Maybe people should be left on their own to live or die, to kill or be killed, left to live under their own rules and moral structures, regardless of how we judge them.

Meredith F. Small is an anthropologist at Cornell University. She is also the author of "Our Babies, Ourselves; How Biology and Culture Shape the Way We Parent" (link) and "The Culture of Our Discontent; Beyond the Medical Model of Mental Illness" (link). Her Human Nature column appears each Friday on LiveScience.