ScienceWeek

SOCIAL SCIENCE: ON THE EVOLUTION OF HUMAN COOPERATION

The following points are made by Joseph Henrich (Science 2006 312:60):

1) Explaining the scale, diversity, and historical dynamics of human cooperation is increasingly bringing together diverse empirical and theoretical approaches. For decades, this challenge has energized evolutionary and economic researchers to ask: Under what conditions will decision-makers sacrifice their own narrow self-interest to help others? Although classic evolutionary models based on relatedness and reciprocity have explained substantial swaths of the cooperation observed in many species, including our own, theoretical work in the 1980s demonstrated that the puzzle of cooperation in large groups, or in situations without much repeated interaction, remained unsolved and would likely require alternative theoretical formulations [1,2].

2) Such cooperative dilemmas, or "public goods" problems, involve situations in which individuals incur a cost to create a benefit for the group. In our society, think of recycling, buying a hybrid car, valor in combat, voting, and donating blood. The dilemma arises from free-riders who enjoy the group benefits created by the contributions of others without paying the costs. Even if nearly everyone is initially cooperative and contributes, free-riders can profit and proliferate, leading to the eventual collapse of cooperation. So, understanding how public goods problems can be solved has provoked great interest, both because human societies have somehow managed to solve many such problems to varying degrees, and because some of the world's most pressing issues, such as global climate change, are essentially public goods dilemmas. New work [3] takes an important step in understanding how self-sustaining cooperative institutions may have emerged over the course of human history.

3) Recent models have demonstrated how evolutionary processes (genetic or cultural) can maintain cooperation in large groups or without repeated interaction. Costly signaling models have shown how cooperation by "high-quality individuals" (those who are potentially desirable as allies or mates) can be sustained if such individuals can accurately signal their quality by making substantial cooperative contributions to public goods [4]. For example, great hunters might supply all the meat for a public feast, or millionaires might donate a recreational center to their community. Similarly, reputation-based models have shown how cooperation can be sustained if individuals' reputations for not contributing to public goods reduce their payoffs (or fitness) by altering how others treat them in certain dyadic social interactions [5]. Finally, models that allow individuals to both contribute to the public good and to sanction noncontributors have revealed stable cooperative solutions, especially when the strategies for cooperation and punishment are influenced by social learning. Thus, a number of possible stable solutions to the puzzle of cooperation in large groups, or cooperation without repeated interaction, have now emerged.

4) It turns out, however, that finding a stable solution is only the first step in confronting the dilemma of cooperation. Each of the above approaches can actually stabilize any behavior or practice, independent of whether it delivers any benefit to anyone. This includes behaviors that reduce the payoff or fitness of the group. For example, instead of public goods contributions, costly signaling could maintain behaviors involving dangerous physical feats (like scaling icy mountain peaks), aggressive displays (like beating up your neighbor), or extravagantly wasteful feasts. Similarly, the same reputational and sanctioning mechanisms that can stabilize cooperation can also sustain maladaptive practices such as consuming the brains of dead relatives, flattening the foreheads of infants, or binding the feet of young girls. Thus, there are actually a multitude of stable equilibria, only some of which are cooperative. What determines which equilibria emerge and/or spread?

References (abridged):

1. R. Boyd, P. J. Richerson, J. Theor. Biol. 132, 337 (1988)

2. N. V. Joshi, J. Genet. 66, 69 (1987)

3. Ö. Gürerk, B. Irlenbusch, B. Rockenbach, Science 312, 108 (2006)

4. H. Gintis, E. A. Smith, S. Bowles, J. Theor. Biol. 213, 103 (2001)

5. K. Panchanathan, R. Boyd, Nature 432, 499 (2004)

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