NEW YORK (NYT NEWS SERVICE ).- Napoleon Chagnon, a cultural anthropologist whose studies of the indigenous Yanomami people of the Amazon rainforest made them famous but whose methods provoked intense disputes among other anthropologists, died Sept. 21 in Traverse City, Michigan. He was 81.

His death, in a hospital, was confirmed by his granddaughter Caitlin Machak. No specific cause was given.

Chagnon proved controversial over his use of genetics and evolutionary theory to explain the behavior of the Yamomani, whose ways Westerners found exotic, to say the least.

In his paper “Life Histories, Blood Revenge, and Warfare in a Tribal Population,” published in the journal Science in 1988, Chagnon — though the surname is French, his family used an Anglicized pronunciation, SHAG-non — asserted that tribal societies were not typically peaceful, challenging a widespread view.

Anthropologists go wrong, he wrote, when they ignore evidence that aggression among men in tribal societies is so highly rewarded that it becomes an inherited trait.

Yamomani life was one of “incessant warfare,” he wrote. His data, collected over decades, he said, showed that 44% of Yamomani men over 25 had participated in killing someone, that 25% of Yanomami men were killed by other Yanomami men, and that men who killed were more highly esteemed and had more wives and children than men who did not.

Chagnon dismissed as “Marxist” the widespread anthropological belief that warfare in tribal life was usually provoked by disputes over access to scarce resources.

“The whole purpose and design of the social structure of tribesmen seems to have revolved around effectively controlling sexual access by males to nubile, reproductive-age females,” he wrote in his 2014 memoir, “Noble Savages.”

Other anthropologists rejected these assertions as exaggerated and even racist, saying they could do harm to the tribe by casting it in a bad light. Many argued that human behavior was best explained not by genetics and evolution but by the social and natural environments in which people live.

Still, Chagnon found a wide audience for his views. His ethnographic study “Yanomamö: The Fierce People” was published in 1968 and turned into a textbook that is widely described as the best-selling anthropology text ever.

In other books, and in interviews, he described his research in the Amazon jungle in swashbuckling terms, citing threatening snakes, jaguars and naked men armed with arrows no less sharp because their points were made of wood.

He visited the Yanomami year after year for months at a time, learning to communicate with them. Members of the tribe gave him the nickname Shaki, which Machak translated as “pesky bee” — a sobriquet he won, she said, because he was always pestering people with questions. His friends and colleagues called him Nap.

As his work received more and more attention, it drew increasing criticism from people ready to argue over practically anything about it, even the way he spelled the name of the tribe: Yanomamö.

The most serious attack came in 2000, in the book “Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon,” by Patrick Tierney, a journalist. Tierney accused Chagnon and a colleague of a wide range of misdeeds, including worsening a measles epidemic in the tribe to test their genetic theories and giving the Yanomami weapons that raised the level of tribal violence.

Some fellow anthropologists rose to Chagnon’s defense. Tierney’s accusations were “lies,” said Raymond Hamm, a professor of anthropology at the University of Nebraska-Lincoln, who studied with Chagnon and often accompanied him into the field. In a telephone interview, Hamm said that far from encouraging an outbreak, Chagnon brought vaccines into the jungle in the hope of preventing disease.

And, Hamm recalled, while Chagnon would “essentially introduce” items that would make Yanomami life easier, like steel machetes and axes or aluminum pots, he instructed Hamm not to share anything having to do with the shotguns they took into the bush.

“Nap said, ‘Don’t even give the shot to them to use as sinkers on the fishing line,’ ” Hamm said.

Other anthropologists, too, disputed accusations in the Tierney book, which was excerpted in The New Yorker. Still, the American Anthropological Association decided that the questions about Chagnon’s work merited an investigation, and in 2002 it issued a report criticizing his depictions of the Yanomami and his dealings with certain government officials. (In 2005, however — without commenting on the merits of the criticism — the association rescinded the report, saying the way the investigation had been conducted had not met its standards.)

In 2012, Chagnon was elected to the National Academy of Science, the nation’s most prestigious scientific organization — an honor that his supporters proclaimed as a vindication.

Napoleon Alphonseau Chagnon was born Aug. 17, 1938, in Port Austin, Michigan, the second oldest of 12 children of Rollin and Mildred Elizabeth (Cavanaugh) Chagnon. His father operated a funeral home, and his mother was a homemaker.

He entered the Michigan College of Mining and Technology intending to study physics but transferred after his freshman year to the University of Michigan, where he discovered courses in cultural anthropology. “I was hooked,” he said in a 2014 interview reported in Proceedings of the National Academy of Science.

He completed his master’s and doctoral degrees at Michigan while his wife, Carlene (Badgero) Chagnon, gave birth to their son and daughter.

Chagnon began his research in the Amazon as a graduate student in 1964, when he traveled to the Venezuela-Brazil border area on a 17-month expedition to the jungle territory of the Yanomami.

In an email, his daughter, Lisa Chagnon Cheponis, recalled an early research trip on which the family spent time with the Yanomami. Chagnon built a mud hut for his family, she said, and tribe members “would freely come in to watch us, for we fascinated them, with our weird pale skin and clothing.”

Chagnon eventually decided that his family would have to leave the jungle, his daughter said, in part because tribesmen made it known that “they wanted to trade something for me and keep me.”

Chagnon taught at Michigan as well as at Pennsylvania State University, Northwestern University and the University of California at Santa Barbara, where he retired in 1999. After his election to the National Academy of Science, he was appointed as a research professor of anthropology at the University of Missouri, a position he held until earlier this year.

In addition to his wife, his daughter and his granddaughter Machak, Chagnon, who lived in Traverse City, is survived by a son, Darius; four other grandchildren; and three step-grandchildren.

Machak, a filmmaker, said she was working with the Smithsonian Institution to archive and preserve years of films her grandfather had made in Amazonia, some of which are considered classics of anthropological filmmaking.

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