In sum, results from experimental economics games can be highly illuminating and useful for many purposes, but just like any kind of behavioral data, they have limitations. It is doubtful that experimental economic results actually reveal much of anything about how people are adapted for one-shot anonymous interactions, and they should not be regarded as evidence about the relevance of the individual as a vehicle of selection in ancestral environments.

I also found myself a little distracted by what seemed like moralistic overtones in the book’s prose style. For instance: “The moral, generous, and civic-minded predispositions documented… in the pages that follow show that evolution can not only foster self-interest but also promote the generous and ethical behaviors that help us escape the prisoner’s dilemma and avert the tragedy of the commons, and that permit us to sustain the hope for a society committed to freedom and justice for all” (p. 7). The message seems to be that “self-interest” (or more accurately, adaptations designed to promote individual fitness) could never lead to such desirable outcomes as generosity, ethical behavior, freedom, and justice; therefore, unless we want to claim that such great things are impossible or illusory, we had better accept a group selectionist view. One problem here is that all such virtues are in fact entirely compatible with individual-level theories of cooperation (e.g., reciprocal altruism, indirect reciprocity, n-person reciprocity, partner choice and positive assortment, costly signaling), and there’s no good reason for suggesting otherwise. Another problem is that the language used by Bowles and Gintis seems to imply, inappropriately, a kind of moral obligation on the part of the reader to accept the group selectionist view.

In summary, the book is valuable both as a review of the anthropological and economic literatures on cooperative behavior, and as an impressive collection of formal models for how such behavior may in theory have evolved. But we have to remind ourselves that formal models are just as theoretical as verbal models. People sometimes seem to treat the output of formal models as data in and of itself, and to overlook that the data we are actually trying to predict are those describing the cooperative psychology of real humans. To the extent that any formal model allows us to make unique, accurate predictions about this psychology—under ecologically valid circumstances—it should be regarded as indispensible. For the time being, however, individual-level theories seem to outshine group selection when it comes to illuminating human biological adaptations for cooperation.