Competition Among Cooperators: Altruism and Reciprocity

Colloquium Competition among cooperators: Altruism and reciprocity Peter Danielson* Centre for Applied Ethics, University of British Columbia, Vancouver, BC, Canada V6T 1Z2 Levine argues that neither self-interest nor altruism explains ex- quite widely, to include sometimes counterintuitive possibilities. perimental results in bargaining and public goods games. Subjects’ [This is the critical justification for Binmore’s (6) harsh criticism preferences appear also to be sensitive to their opponents’ per- of Axelrod (2, 7).] In particular, when we specify the mechanisms ceived altruism. Sethi and Somanathan provide a general account of reciprocity, we shall see that they have surprises in store for of reciprocal preferences that survive under evolutionary pressure. us (8). Although a wide variety of reciprocal strategies pass this evolu- The present paper runs a similar line of inquiry with a new tionary test, Sethi and Somanthan conjecture that fewer are likely starting point. We begin with Levine’s account of human coop- to survive when reciprocal strategies compete with each other. erative behavior in experiments using bargaining and public This paper develops evolutionary agent-based models to test their goods games. Although it is commonly agreed that self-interest conjecture in cases where reciprocal preferences can differ in a will not account for these experimental results, Levine goes variety of games. We conﬁrm that reciprocity is necessary but not further and argues that simple altruism is also inadequate. A sufﬁcient for optimal cooperation. We explore the theme of better fit is obtained from preferences that are sensitive to one’s competition among reciprocal cooperators and display three in- opponents’ perceived altruism. Thus, Levine argues that a kind teresting emergent organizations: racing to the ‘‘moral high of reciprocity of altruism is required to explain human cooperative behavior. Sethi and Somanathan (9) modify the reciprocal ground,’’ unstable cycles of preference change, and, when we component of Levine’s construction to achieve evolutionary implement reciprocal mechanisms, hierarchies resulting from ex- stability under a variety of selective regimes. They raise the ploiting fellow cooperators. If reciprocity is a basic mechanism question of what would happen were various reciprocal coop- facilitating cooperation, we can expect interaction that evolves erators placed in competition with each other. around it to be complex, non-optimal, and resistant to change. To attempt to answer this question, we constructed two kinds of models. In the first set of models, agents are capable of quite he topic for this colloquium is competition and cooperation complex preference interactions. They can be altruistic toward Tas factors in emergent human organization. Sober and others and react to other agents’ altruism and reaction functions. Wilson (1) note that the behavior labeled ‘‘cooperation’’ by The agents in the second set of models have simpler interactions, evolutionary game theorists is the same as that discussed in the as they implement working reciprocal strategy mechanisms evolution of altruism literature. So our topic can be taken very rather than preferences. We test these agents in a variety of generally; indeed, it is ‘‘the central theoretical problem of situations. (We use eight commonly discussed two-by-two sociobiology’’ (1). Naturally, the main question is how is altru- games.) Although we confirm the basic result that reciprocity ism͞cooperation possible among agents selected by competitive allows agents to cooperate where neither self-interested nor evolutionary processes. But this possibility question can be simple altruistic agents would, we also discover that some forms misleading. For example, both Axelrod (2) and Gauthier (3) of reciprocity lead to unexpected—emergent—social structures. advanced the discussion of these issues by insisting that there are Some reciprocally altruistic agents can race to the moral high situations in which cooperative agents responsive to the behavior ground, and, ironically, treat ‘‘less altruistic’’ agents exploit- atively. Others are trapped in cycles of preference change. or disposition of their opponents do as well or better than Finally, although reciprocity is necessary to stable cooperation, straightforwardly competitive agents. Yet each defended a single it need not be optimal. When we implement one family of simple cooperative strategy—Tit for Tat and Constrained Maximiza- reciprocal mechanisms, exploitative hierarchies emerge as well tion, respectively—that is not a unique equilibrium. [Of course, as equal cooperative outcomes. in Gauthier’s case, critics point out that Constrained Maximi- zation doesn’t even claim to be an equilibrium strategy (4). The Previous Work extended preference concepts discussed below can be seen as a In this section, we discuss only the immediate ancestors of the way to avoid this criticism.] Neither attended to the competition present paper; see ref. 10 for a broader survey of the literature between cooperative strategies and both neglected less ‘‘nice’’ alternative strategies. In earlier work (5), I extended Gauthier’s model to address This paper results from the Arthur M. Sackler Colloquium of the National Academy of competition among cooperators, finding that what I called Sciences, ‘‘Adaptive Agents, Intelligence, and Emergent Human Organization: Capturing Complexity through Agent-Based Modeling,’’ held October 4–6, 2001, at the Arnold and ‘‘reciprocal cooperators,’’ who demand discriminatory respon- Mabel Beckman Center of the National Academies of Science and Engineering in Irvine, CA. siveness from cooperative partners, exploit some more tolerant *E-mail: [email protected]. cooperators, and thereby supplant nicer Constrained Maximiz- †Although it is not surprising that, as agents, we encourage others to cooperate, it must be ers. More generally, the combination of evolution, altruism, and stressed that the values cooperation (pareto) optimizes are local (evidently, typically reciprocity need not result in populations of equal, optimal, and within range of our encouragements). As social scientists, we seek to understand coop- tolerant cooperators. Most generally, because we’re inclined to eration’s causes and constituent mechanisms. As applied social scientists (applied ethi- favor cooperation, we need methods that challenge our intuitive cists), we will sometimes seek to encourage cooperation and sometimes to undermine it. † (Think of the original story of the prisoner’s dilemma.) So we can account for a bias toward biases. Evolutionary simulation can be a good test because cooperation, but it is a bandwagon we should be cautious about riding. We need good evolution builds in strong competitive pressure. But simulations tools to disengage our theoretical ethical intuitions from our moralistic responses and can easily confirm biases, unless we allow the generator to range then to isolate, test, and improve new moral mechanisms. www.pnas.org͞cgi͞doi͞10.1073͞pnas.082079899 PNAS ͉ May 14, 2002 ͉ vol. 99 ͉ suppl. 3 ͉ 7237–7242 Downloaded by guest on October 1, 2021 on rationality and evolution. This paper builds on two recent Table 1. Eight sequential game outcomes streams of research. First, Levine (11) asks ‘‘to what extent can a simple model of players who are not selfish explain the data from a variety of experiments, including both ultimatum and public goods games?’’ Following Levine, we construct interact- ing utility functions that have parameters for both pure altruism and a reciprocity factor, ␭. ‘‘When ␭ Ͼ 0, the model can be regarded as incorporating an element of fairness, . One of our OR 3,3 1,2 2,1 0,0 major conclusions is that ␭ ϭ 0 [pure altruism] is not consistent CO 3,3 0,0 0,0 2,2 with data from the ultimatum game’’ (11); therefore, according KS 0,3 1,2 2,1 3,0 to Levine, experiments reveal that human players are spiteful as AG 2,0 1,1 3,3 0,2 well as altruistic and this can be accounted for by preferences PD 2,2 0,3 3,0 1,1 that reciprocate something. (That is, preferences that are not UPD 3,2 0,3 4,0 1,1 exogenous but are instead functions of some feature of the BS 1,3 0,0 0,0 2,1 opposing player. Throughout this paper, ‘‘opposition’’ denotes CK 4,4 1,5 5,1 0,0 pairing in games without prejudice to the player’s interests or preferences; opponents need not be competitors.) The question arises, what do they reciprocate? common knowledge. Players know each other’s preferences, Second, Sethi and Somanathan (9) introduce an additional including their altruistic and reciprocal components. test: ‘‘survival under evolutionary pressure.’’ Their work takes (iv) All players have the same formal preference function, Guth and Yaari’s (12) evolutionary approach to preferences: which includes arguments for other’s altruistic and reciprocal ‘‘instead of assuming that individual preferences are exogenously parameters. Players differ only in the value of their altruistic and given, we think of an evolutionary process where preferences are reciprocal parameters. This assumption may seem inconsistent determined as evolutionarily stable strategies.’’ In this approach, with our evolutionary approach. Of course, it would be better to ‘‘reproductive success is purely a function of the resources have a more constructive model, where the altruistic and recip- earned via strategic interaction,’’ whereas preferences only de- rocal apparatus evolves. We move in this direction below. termine agent’s moves. I use this approach

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