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This chapter examines the evolutionary roots of the proximate psychological mechanisms that underlie cooperation. The idea that there are specific biological mechanisms behind at least some aspects of cooperation is supported by recent work in behavior genetics. One common technique in behavior genetics is to compare identical twins to fraternal twins. Another study, using a different technique, found a relationship between voter turnout and two specific genes. Hormones provide another window onto the proximate psychological mechanisms underlying cooperation. The chapter first considers the most basic form of cooperation, reciprocity, before discussing its relation to culture, the avoidance of individuals prone to free riding, and detection of cheaters. It also explores indirect reciprocity, generosity as performance, and hard-to-fake signals.

This chapter examines the sociobiology of human cooperation. Given the tendency of people to copy the successful and the fact that natural selection favors the more fit, the chapter asks how our altruistic preferences overcame the cultural and biological evolutionary handicaps entailed by the reduced payoffs that they elicited. To answer this question, two major biological explanations of cooperation are discussed: inclusive fitness in either a kin-based or a multi-level selection model, and reciprocal altruism and its indirect reciprocity and costly signaling variants. The chapter explores a model of inclusive fitness based on group differentiation and competition, clarifying what is meant by multi-level selection and how it works. It also discusses models that address equilibrium selection, the link between standing strategy and indirect reciprocity, and positive assortment. Finally, it assesses the mechanisms and motives underlying helping behavior.

This chapter explores the specificities, strengths, and weaknesses of the idea of reciprocity as a basis for intergenerational obligations. Three models are presented: descending, ascending, and double reciprocity. Each of these three models is tested against three objections. The first objection asks why having received something from someone would necessarily entail the obligation to give back. The second objection questions the ability of each model to justify the direction of reciprocation. A final objection looks at the extent to which reciprocity-based views adjust the content of our obligation to the fluctuations in population size.

This chapter explores how and why humans exhibit morality. It considers the influence of group competition on human evolution as well as Richard D. Alexander's concept of indirect reciprocity, its biological bases, and its manifestations as morality. It analyzes Alexander's argument that moral systems are systems of indirect reciprocity and that systems of indirect reciprocity become automatically moral systems. Alexander views moral systems as guides of actions, or standards of conduct, that are distinct from the concept of morality. The chapter includes an excerpt from Alexander's 1987 book The Biology of Moral Systems, which tackles the biological underpinnings of human prosociality and its dark sides of ingroup-outgroup antipathy, along with discriminate and indiscriminate beneficence involved in human nepotism.

This chapter reviews and evaluates accounts of how the mental mechanisms that dispose people to emit uniquely human forms of prosocial behavior evolved, beginning with Boehm’s proposition that morality originated when subordinate members of hierarchically-ordered groups of early humans banded together to suppress the selfishness of dominant members. Alexander’s proposition that altruistic dispositions were selected when simple systems of direct reciprocity became expanded into complex systems of indirect reciprocity is then discussed. Following this, the controversy between theorists who account for uniquely human prosocial behaviors in terms of gene-culture co-evolution and theorists who account for them in terms of individual selection is reviewed.

This chapter reviews theory and research on the evolution of several forms of cooperation, including incidental helping, mutualism, sharing, turn-taking, direct reciprocity, and indirect reciprocity. Although game theorists have found that Tit for Tat reciprocity is a winning strategy in conducive contexts, evidence of reciprocity among social species other than humans is relatively rare. Kinder, gentler forms of reciprocity that enable players to correct their mistakes and that induce them to forgive those who have cheated them once produce greater gains than inflexible Tit for Tat strategies do. One of the keys to understanding how cooperative strategies have evolved is to recognize the significance of selective interaction. Evolutionary theorists have accounted the tendency for people to help their friends over long periods of time without any expectation of immediate return in terms of the value of upholding beneficial relationships, cultivating credit, and fostering long-term security.

In most primate societies, individuals have long-lasting relationships with other members of their groups. Individual monkeys often have preferred grooming partners and reliable allies. If allies and grooming partners were always relatives, we could explain such cooperation with inclusive fitness and move on. But these cooperative relationships involve unrelated individuals. How can natural selection lead to such behavior in the absence of kinship? One answer is reciprocity: I'll scratch your back if you scratch mine. The essential feature of reciprocity is contingent cooperation. The concept of reciprocity took off in 1981 when Robert Axelrod and W. D. Hamilton published a paper in Science that analyzed a formal model of reciprocal altruism. This chapter examines both the basic Axelrod-Hamilton model of reciprocity and some of the more important developments since, including the importance of mistakes, the effect of partner choice, indirect reciprocity, kinship, mutants, Tit-for-Tat strategy, and the roles of reciprocity and altruistic punishment in solving collective action problems. The chapter also explains how to build and solve models of repeated interactions.

Subsequent chapters in this volume deal with populations as dynamic entities in time and space. Populations are, of course, made up of individuals, and the parameters which characterize aggregate behavior—population growth rate and so on— ultimately derive from the behavioral ecology and life-history strategies of these constituent individuals. In evolutionary terms, the properties of populations can only be understood in terms of individuals, which comes down to studying how life-history choices (and consequent genefrequency distributions) are shaped by environmental forces. Many important aspects of group behavior— from alarm calls of birds and mammals to the complex institutions that have enabled human societies to flourish—pose problems of how cooperative behavior can evolve and be maintained. The puzzle was emphasized by Darwin, and remains the subject of active research today. In this book, we leave the large subject of individual organisms’ behavioral ecology and lifehistory choices to texts in that field (e.g. Krebs and Davies, 1997). Instead, we lead with a survey of work, much of it very recent, on five different kinds of mechanism whereby cooperative behavior may be maintained in a population, despite the inherent difficulty that cheats may prosper by enjoying the benefits of cooperation without paying the associated costs. Cooperation means that a donor pays a cost, c, for a recipient to get a benefit, b. In evolutionary biology, cost and benefit are measured in terms of fitness. While mutation and selection represent the main forces of evolutionary dynamics, cooperation is a fundamental principle that is required for every level of biological organization. Individual cells rely on cooperation among their components. Multicellular organisms exist because of cooperation among their cells. Social insects are masters of cooperation. Most aspects of human society are based on mechanisms that promote cooperation. Whenever evolution constructs something entirely new (such as multicellularity or human language), cooperation is needed. Evolutionary construction is based on cooperation. The five rules for cooperation which we examine in this chapter are: kin selection, direct reciprocity, indirect reciprocity, graph selection, and group selection. Each of these can promote cooperation if specific conditions are fulfilled.

Many disciplines find it puzzling that costly cooperation exists within groups of non-kin. Cooperation can be sustained when non-cooperators are punished or when cooperators are rewarded, but these sanctions are themselves costly to provide. Many theoretical models rely on “second-order punishment”, which means that people will punish those who do not punish non-cooperators. However, our review of the evidence suggests that people do not readily do this, and do not particularly like punishers. By contrast, people will readily reward those who reward cooperators. So what does sustain punitive sentiment? Punishment may function to signal qualities of the punisher that are otherwise difficult to observe, such as the punisher’s trustworthiness or willingness to retaliate against personal affronts. Alternately, punishment may simply be a “Volunteer’s Dilemma” where it becomes rational to “volunteer” to punish non-cooperators if no one else in the group will. Finally, the chapter discusses how positive and negative sanctions may function differently to maintain large-scale human cooperation.

The problem of climate change has generated renewed interest in the question of what we owe to future generations. This question is often thought to pose special problems for contractualists, because many claim that there is no possibility of mutually beneficial cooperation between generations. Because benefits can flow only forward in time, there cannot be reciprocity between non-contemporaneous generations, and so there is no place for a social contract to determine how the benefits and burdens of cooperation are to be assigned. This chapter argues that this supposed problem for contractualism is not really a problem at all, since there is no problem in principle, or in practice, with a system of intergenerational cooperation in which benefits flow only one way. The widespread failure to appreciate this is due to several counterintuitive features of the system that is at work in our society.

This chapter introduces a 1986 article by Richard D. Alexander entitled “Ostracism and Indirect Reciprocity: The Reproductive Significance of Humor,” in which he tackles the social-evolutionary significance of humor. It considers Alexander's belief that evolutionary reasoning and analytic hypothesis-testing methods can and should be applied to all human phenomena, even the most seemingly arbitrary and far removed from survival and reproductive functions. Alexander proposes and evaluates a suite of ideas concerning the role of humor in human social interactions ranging from displays of social-linguistic prowess, ingroup-outgroup manipulations, tests of social-intellectual skill, and strong links to mental scenario-building—all of which revolve around his central thesis of shifting balances of social competition and cooperation as prime movers of human evolution.

This chapter discusses what reputation is and why and how we are struggling for it. Reputation can be considered a form of currency, and our reputation determines whether or not other people invest in us, buy from us, or give us some kind of reward. Indirect reciprocity is an efficient evolutionary mechanism that has led to the emergence of reputation. In the Internet age, digital reputation plays a particularly important role. After a brief discussion about the measurement of reputation, the chapter turns to the rules of the ranking games that scientists and artists play. The rules for these players are better elaborated than the rules for other communities. The illusion and manipulation of objectivity is discussed and related to two of the most prestigious awards: the Nobel Prize and the Academy Award. A recurring perspective in the book, namely the navigation between objectivity and subjectivity, is analyzed, here in the context of the nomination and selection processes for each award. The author then turns to digital reputation. Since a big industry has emerged with the goal of making websites more visible, the search engine manipulation effect and its possible impact is discussed.

There is typically considerable between-individual variation in trait values in natural populations. Game theory has often ignored this, treating individuals as the same. However, the existence and amount of variation is central to many predictions in biological game theory, as this chapter illustrates. Variation is central to signalling systems and stabilizes these systems as well as extensive-form games. Variation leads to individuals taking a chance that a partner is better than average; for example, promoting cooperation in a finitely repeated Prisoner’s Dilemma game. When there is both variation and within-individual consistency, so that past behaviour is predictive of current behaviour, reputation is important. As is demonstrated, once population members respond to reputation, this then selects for all to modify their behaviour so as to change their reputation and so change how others interact with them in the future, with consequences for the level of cooperation in the population. Furthermore, as a game of trust shows, the extent to which reputation matters can depend on whether individuals are prepared to pay the cost of being socially sensitive, which depends on the amount of variation. Variation selects for individuals to be choosy about their partner, and choosiness can lead to assortative pairing in a population, again promoting cooperation. The importance of choosiness in a market situation is demonstrated by a model in which partners have to decide how much to commit to one another, with factors that enhance choosiness leading to higher levels of commitment.

There are several key ideas that appear in almost all of John Holland's writings on artificial and natural complex adaptive systems: internal models, default hierarchies, genetic (evolutionary) algorithms, and recombination of building blocks. One other mechanism, which is linked to all of those, is tag-based interaction. Perhaps the first use of tag-based interaction (though it was not so named) can be found in Holland's "broadcast system," [26] a formal specification of an architecture suitable for modeling adaptation of open-ended, parallel processes. Tag-based interaction mechanisms next played a key role in classifier systems [30, 32]. In classifier systems, a tag acts as a kind of "address" of one or more classifier rules (productions), enabling rules to send messages to selected sets of rules, and allowing rules to select which messages they will respond to. Thus, tags provide a way to structure computations, making it possible to prove that classifier systems are computationally complete [18], to various neural network architectures [8, 55] and even to abstract models of immune systems [17]. Tags also are used to form coupled chains of classifiers, to construct subroutinelike structures, and to allow Holland's Bucket Brigade algorithm to efficiently allocate credit to "stage setting" rules [9, 30, 50]. Holland has also described how tagged classifiers might be used to form default hierarchies and other more complex internal models [28, 30, 33, 46]. More generally, Holland has emphasized the key role that tag-based interaction mechanisms have in almost all complex adaptive systems (CAS), i.e., systems composed of limited capability agents who interact to generate systemlevel behavior [31]. In the context of CAS, tags are arbitrary properties or traits of agents which are visible to other agents, and which agents can detect and use to condition reactions to other tag-carrying agents. Tags can be agent features, such as surface markings, or they can be agent behaviors, from behavioral routines in animals to more complex behaviors of humans, e.g., wearing particular clothes, carrying flags, or following religious customs [3, 31, 53]. Since agents can have different tags, and since arbitrary tags can come to be associated with particular types of agents (with their own interaction and behavioral patterns), tags can take on "meanings" by virtue of the types of agents who display each particular tag, i.e., as a result of the other behavioral traits those agents tend to have.

This chapter studies how social ranking in humans emerged as the result of an evolutionary process. It starts with the story of the discovery of pecking order among chickens by a Norwegian boy. Both animals and humans need a healthy balance between cooperation and competition to ensure evolutionarily efficient strategies. The biological machinery behind social ranking is discussed. There are two distinct mechanisms for navigating the social ladder: dominance and prestige. Dominance, an evolutionarily older strategy, is based on the ability to intimidate other members in the group by physical size and strength. The group members don’t accept dominance-based social rank freely, only by coercion. Members of a colony fight, and the winners of these fights will be accepted as “dominants” and the losers as “subordinates.” The naturally formed hierarchy serves as a way to prevent superfluous fighting and injuries within a colony. Prestige, as a strategy, is evolutionarily younger and is based on skills and knowledge as appraised by the community. Prestige hierarchies are maintained by the consent of the community, without pressure being applied by particular members. The mechanisms of forming and maintaining social hierarchies are described. Social structures, both hierarchies and network organizations, are reviewed. Discussion of these structures is carried over to social and political history and the tension between democracy and authoritarianism.