Joseph Henrich & Natalie Henrich 
Why Humans Cooperate [PDF ebook] 
A Cultural and Evolutionary Explanation

Cooperation among humans is one of the keys to our great evolutionary success. Natalie and Joseph Henrich examine this phenomena with a unique fusion of theoretical work on the evolution of cooperation, ethnographic descriptions of social behavior, and a range of other experimental results. Their experimental and ethnographic data come from a small, insular group of middle-class Iraqi Christians called Chaldeans, living in metro Detroit, whom the Henrichs use as an example to show how kinship relations, ethnicity, and culturally transmitted traditions provide the key to explaining the evolution of cooperation over multiple generations.