Napoleon Chagnon's ethnography
Yanomamö: The Fierce People is the best-selling anthropological book of all time.
In his book Chagnon implies (based on the data he collected) that the most violent and aggressive males, of the Yanomamö won the most copulations thus passed on their genes for "fierceness." Chagnon's work has been attacked, most notably by Journalist Patrick Tierney, in his book, Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon. Yet if you read Chagnon's works you come to understand that most of Tierney's attacks are unfounded, Chagnon has been careful to base his conclusions on his data.