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252 • MacroeconomicsThis suggests that cooperation has evolutionary origins, and indeednumerous studies from the field of evolutionary biology support this notion.For example, if you throw a bunch of Pseudomonas fluorescens bacteriain a beaker, mutations emerge that exhibit cooperative behavior (see Box13.5). Such cooperative behavior is also evident in higher-level organismsand lends the species exhibiting it a selective advantage (see Box 13.6).Among humans, evolution takes place at the cultural level as well,which is far more relevant to policy. Human culture has a profound impacton human behavior, as can be surmised from the numerous experimentsand studies described above, and cultures are constantly evolving.Different cultures evolve different economic institutions, and when thoseinstitutions reinforce adaptive behavior, those cultures are more likely topersist. If a culture consists of independent family groups with little socialor economic interaction and few gains from cooperation, then selfish behaviormay be quite adaptive. If a culture consists of larger social units andan economic system that enjoys gains from cooperation, such as a whalehunting society, then cooperative behavior may be most appropriate.Box 13-5The Evolution of CooperationThrow a bunch of Pseudomonas fluorescens bacteria in a beaker, andthey will rapidly reproduce until they become starved for oxygen. At thispoint, the survival advantage shifts to a mutant type known as the“wrinkly spreader,” which can create a film that binds them together intoa floating colony with access to oxygen from above and nutrients frombelow. Cooperation allows the group to thrive. However, within this cooperativecolony there may be some defectors; they produce none of thesustaining film, but instead free-ride on that produced by others. Withthe energy they save by not producing the film, they are able to havemore offspring than the cooperative Pseudomonas. Competitive individuals(i.e., defectors) within the group outcompete cooperative ones.However, if there are too many defectors, the colony can no longer stayafloat and plunges to the depths of the beaker, losing its relative fitness.Colonies with fewer defectors will continue to thrive and leave more descendantsthan others. a What we see is two distinct types of evolutionarypressure, at the individual and group level. The basic rule is that “Selfishnessbeats altruism within single groups. Altruistic groups beat selfishgroups.” ba D. Wilson, Evolution for Everyone: How Darwin’s Theory Can Change the Way We ThinkAbout Our Lives, New York: Delacorte Press, 2007.b D. Wilson and E. Wilson, Rethinking the Theoretical Foundations of Sociobiology,Quarterly Review of Biology 82:327–348 (2007), esp. p. 345.