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This chapter is about the prisoner's dilemma as a repeated encounter. The best strategy is defection, or non-cooperation, if a single encounter is anticipated. In the event of repeated, or iterated play, evidence indicates that cooperation can evolve. The introduction to this chapter provides a story published following the death of the last British survivor of the Christmas truce from World War I in 1915. Much of the chapter is based on Robert Axelrod's contests that inspired his classic book, The Evolution of Cooperation. Axelrod's first tournament involved fifteen contestants from different disciplines competing in a round-robin tournament with 200 games, competing against each opponent submitting strategies for playing the prisoner's dilemma. There was a great variety in how the games went but the winner was the one with the simplest plan, which was based on the simple strategy in tit-for-tat. This strategy worked initially then the competitor was to do whatever his opponent did on their previous move. Axelrod ran a much larger second tournament, with sixty-two entrants from six countries. The strategy of tit-for-tat again won, defeating experts from many fields. Subtopics follow the main part of the chapter, including a look at how cooperation takes hold and difficulties; robustness; noise; and cooperation examples. A supplement comes from Axelrod's book that is research on prisoner's dilemma leading to cooperation emerging in many isolated areas along the trenches in the early stages of World War One.

The global community faces several very pressing environmental challenges such as climate change, depletion of the high-sea fisheries, and unprecedented rates of biodiversity loss. Governments are in the process of designing environmental policies to address these problems unilaterally, but also collectively (in the form of international agreements). Meanwhile, private citizens and firms are observed to voluntarily take protective action. Whereas standard game theory would predict that formal government intervention can only provide an extra stimulus for protective action, there are many examples of external interventions decreasing agents' propensity to undertake socially desired activities. This chapter provides an overview of the literature on the circumstances under which formal interventions can crowd out voluntary contributions to the common good. Furthermore, it is discussed how the effectiveness of government intervention may be improved by preserving the agents' intrinsic motivation to contribute to the common good.

Previous research in evolutionary game theory has shown that cooperation is not an evolutionarily viable strategy unless additional mechanisms are put into play, as the tragedy of the commons is often the ensuing doomsday scenario. This chapter presents a surprisingly elegant solution to this paradox, resorting to a mathematic model of pathological altruists in a stereotypical noncooperative game: the Prisoner’s Dilemma. Pathological altruists are defined as individuals incapable of changing their altruistic behavior, and hence unresponsive to the stimuli of greed and fear. We show how the presence of pathological altruists induces a polymorphic equilibrium between defectors and cooperators. Whenever selection pressure is weak, a single pathological altruist can obliterate the evolutionary advantage of defectors, thus providing a messianic effect for the community as a whole. Our model does not explicitly address the fundamental question of how pathological altruism emerges, but hints at an a posteriori justification for its viability.

After a long and turbulent history, the study of human cultural evolution is finally becoming comparable to the study of genetic evolution, with human history the counterpart of the biological fossil record. One of the most remarkable products of cultural evolution has been an increase in the scale of human societies by many orders of magnitude. Today, the great majority of humans live in complex societies, which can only exist due to extensive cooperation among large numbers of individuals. Ultrasociality, the ability of humans to cooperate in large groups of genetically unrelated individuals, presents a puzzle to both evolutionary and social theory. Although much theoretical effort has been devoted to understanding the evolution of cooperation in small-scale groups (hunter-gatherers living in societies of hundreds to a few thousand individuals), the same cannot be said about the next phase of human evolution, the rise of complex societies encompassing tens and hundreds of millions of people. Evolutionary biologists, political scientists, anthropologists, and others have proposed a multitude of theories to explain how complex societies evolved. However, scientific study has suffered from two limitations. First, with a few exceptions, theories have relied on verbal reasoning; formal models tend to focus on the evolution of cooperation in small groups, whereas the transition from small- to large-scale societies has been mostly neglected. Second, there has been no systematic effort to compare theoretical predictions to data. Human ultrasociality has evolved repeatedly around the world and across time, reflecting both common selection pressures and the unique contingencies affecting each case. An enormous amount of archaeological and historical information exists but has not been studied from an evolutionary perspective. Thus, explicit models that will yield specific and quantitative predictions are needed as well as databases of the cultural evolution of human ultrasociality. Furthermore, a research program combining explicit models with empirical testing of predictions is not only an academic endeavor. Understanding conditions that either promote or inhibit human ultrasociality is highly relevant for addressing the challenges of large-scale cooperation and conflict in the modern world. Published in the Strungmann Forum Reports Series.

This chapter reviews advances in evolutionary theory since Bowlby and proposes that our capacity for culture emerged with the evolution of human attachment by means of selection for increased mother-infant cooperation in the resolution of parent-offspring conflict. It outlines the evolutionary-developmental logic of attachment, parent-offspring conflict, and the view of culture as “extended embodied minds.” It describes how the embodied mind and its attachments might have been extended beyond the mammalian mother-infant dyad to include expanding circles of cooperative individuals and groups. It argues that because attachment came before and gave rise to culture, no culture could long exist that did not accommodate the attachment needs of its infants. On this view, all the myriad cultural contexts of attachment foster secure-enough attachment—except when they cannot. Theory and evidence show that when mothers and others are unable to buffer their children against environmental risk and uncertainty, insecure attachment can be (or once was) evolutionarily rational. It concludes that an attachment theory fully informed by twenty-first century evolutionary theory is fully consilient with normative emic perspectives on the nature of the child and appropriate child care, in both favorable and unfavorable environments.

The relationship between empathy, love, and compassion has long been contested in the history of moral theory. Drawing on Martha Nussbaum’s definition of compassion as a form of judgement, and its relationship to empathy as both emotive and cognitive, this chapter seeks to uncover some of the reasons why empathy and compassion are still contested by scientists working in moral psychology as being relevant for the truly moral life. It also draws on fascinating work by archaeologists that shows reasonable evidence for the existence of deep compassion far back in the evolutionary record of early hominins, even prior to the appearance of Homo sapiens. The long-term care of those with severe disabilities is remarkable and indicates the importance of empathy and compassion deep in history. This is not so much a romanticized view of the past, since violence as well as cooperation existed side by side, but an attempt to show that the rising wave of anti-empathy advocates have missed the mark. Compassion is the fruit of cooperative tendencies. Primatologist Frans de Waal has also undertaken important work on empathy operative in the social lives of alloprimates. The Thomistic concept of compassion in the framework of his approach to the virtues in the moral life is also discussed.

In the animal world, collective action to shelter, protect, and nourish requires the cooperation of group members. Among humans, many situations require the simultaneous cooperation of more than two individuals. Most of the relevant literature has focused on an extreme case, the N-person Prisoner’s Dilemma. Here we introduce a model in which a threshold less than the total group is required to produce benefits, with increasing participation leading to increasing productivity. It constitutes a generalization of the two-person Stag Hunt game to an N-person game. Finite and infinite population models are studied—in infinite populations a rich dynamics admits multiple equilibria. Scenarios of defector dominance, pure coordination, or coexistence may arise simultaneously. However, populations are finite and when their size is of the same order of magnitude as the group size, the evolutionary dynamics is profoundly affected: it may ultimately invert the direction of natural selection, compared with the infinite population limit.

By 100,000 years ago, humans walked the Earth who were very similar to us physically and genetically, but they lived in small family bands and their culture was much simpler than the culture of any humans living today. The authors argue that these humans had the capacity to participate in more complex cultures and suggest that this capacity evolved because families had to cooperate closely to raise children in times when climate was very variable. Natural selection worked at two levels—on individuals but also on families. Families that were best at cooperating and raising the next generation were most likely to survive. These successful families passed on both their genes and their culture to the next generation. The chapter reviews evidence gained from studies of humans and comparisons of humans and chimpanzees that reveal humans’ unique motivation and ability to work together.

This chapter reflects on the sequence of the book so far, and applies the discussion to some aspects of human life. It is false to say that an arch is explained by the properties of stones. It would still be false to say that an arch is explained by what stones are, even if all arches everywhere were made of stones. Similar observations extend throughout science, and from this it can, and should, be deduced that the moral stature of human beings is neither eroded nor replaced by the study of the physical mechanism of human beings. It is the duty of scientists writing for the general public to make this clear and not fudge it. It is false to say, for example, that the language of justice and responsibility is less objective than statements about wavefunctions coming from physics, or statements about genes in biology.