I sit down to write during the December holiday season. It is a time of giving when many people throughout the world go out of their way to help others. The human tendency to cooperate and help individuals in need, some of who may be total strangers, is a facet of life we all know. Readers unfamiliar with how the broader biological world works may be unaware how unusual this is, and cooperation in the form of altruism, aiding others at personal cost, is difficult to explain evolutionarily. In A Cooperative Species, economists Samuel Bowles and Herbert Gintis set out to explain why humans are an unusually pro-social species and how we have come to be this way.

Their central thesis is that humans cooperate because we are genuinely interested in the well-being of others. Moreover, we will punish individuals who violate social norms and fail to cooperate. They call these tendencies to help and punish “strong reciprocity.” Acting in these ways evolved because our human ancestors occupied and constructed environments where groups of individuals who cooperated survived and reproduced more than others. The first claim deals with the proximate or immediate explanation of pro-social behavior, while the second provides an ultimate or evolutionary explanation for human cooperation. Both claims are controversial because they run counter to standard economic and evolutionary theory that invokes self-interest as the guiding force underlying human activity.

The authors base their proximate argument on experiments that indicate humans do not always operate in ways that benefit themselves. Instead, subjects act fairly and cooperate, often at a personal cost, while punishing others who behave selfishly. Such behavior occurs regardless of whether experiments are conducted in anonymous games played in the laboratory with college students or with subjects across the world. There is considerable variability in these experimental results, with much of the variation mapping onto how people actually live their lives. The tendency for individuals to cooperate in experiments varies as a function of how much their particular society values or depends on helping others.

The cross-cultural variation that emerges from these experiments indicates that we must move beyond biology to understand the evolution of human cooperation. Bowles and Gintis devote most of their discussion to this problem. Here their analyses turn increasingly arcane, depending on mathematical models and computer simulations. Most readers will find these sections tough sledding, but their primary conclusions are easy to understand. Here they argue that the unique ability of humans to transmit knowledge via social learning facilitated the creation of institutions and cultural practices that reinforced group beneficial behaviors and reduced the advantages of individual selfishness, leading to a selective process that favored the evolution of groups of cooperators.

This is an important and timely book. A Cooperative Species addresses a major problem in the biological and social sciences, whose implications extend beyond the narrow confines of academic inquiry. In a rapidly changing world that is increasingly complex and interconnected, the future of humankind may depend on our ability to get along with each other. Read this book for insight into this issue and the theoretically and empirically challenging problems posed by cooperation.