What were our early ancestors really like as they accomplished the transition from hunter-gathering bands to more complex settled societies? The anthropologist Napoleon A. Chagnon may have come closest to the answer in his 35-year study of a remarkable population, the Yanomamö of Venezuela and Brazil.

His new book, “Noble Savages,” has three themes. First, it is a beautifully written adventure story of how Dr. Chagnon learned to survive in an entirely alien culture and environment, among villages locked in perpetual warfare and jaguars that would stalk his tracks through the jungle. Second, it describes the author’s gradual piecing together of how Yanomamö society actually works, a matter of great relevance to recent human evolution. Third, it recounts his travails at the hands of the American Anthropological Association.

Most tribes studied by anthropologists have lost much of their culture and structure under Western influences. In the 1960s, when Dr. Chagnon first visited them, the Yanomamö were probably as close as could be to people living in a state of nature. Their warfare had not been suppressed by colonial powers. They had been isolated for so long, even from other tribes in the Amazon, that their language bears little or no relationship to any other. Consisting of some 25,000 people, living in 250 villages, the Yanomamö cultivated plantains, hunted wild animals and raided one another incessantly.

Trained as an engineer before taking up anthropology, Dr. Chagnon was interested in the mechanics of how the Yanomamö worked. He perceived that kinship was the glue that held societies together, so he started to construct an elaborate genealogy of the Yanomamö (often spelled Yanomani.)