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Aristotle’s function argument suggests that the human good is found in the excellent expression of natural human functions and that virtues are the character strengths that make it possible to fulfill those functions. An evolutionary understanding of human nature recognizes humans as an ultrasocial species that features group living, cooperation, and profound interdependence. Group inclusion was essential to survival and reproduction during human evolution. Therefore, a social exclusion detector is an extremely important adaptation that enables the individual to monitor the threat of ostracism. Social exclusion activates a key part of the neural network that registers physical pain, the anterior cingulate cortex, making social exclusion literally painful. The human function of group living is fulfilled by activities that promote belonging, a central human good. Extensive research documents the essential role of belonging in human flourishing. The primary virtue associated with belonging is loyalty, and belonging is the direct, everyday expression of group membership.

A brief recounting of the complex social capacities I have discussed so far suggests that Aristotle likely had it right in the Politics when he famously said that “man is more of a political animal than bees or any other gregarious animals” (1253a 8–9). We see this political readiness in many ways. Humans are strongly interested in others’ faces and emotions from the first hours of life, and we are deeply oriented toward attachment to other humans. We are “imitation machines,” replicating actions necessary to achieve an outcome but also actions we perceive as intentionally normative. We come to recognize ourselves as separate independent agents, but this appears to be secondary to our ability to see others as independent actors with their own beliefs, emotions, and intentions. We are able to pursue independent goals, but we also pursue joint goals with shared intentionality. We are prolific, highly engaged cooperators. We punish cheaters without direct benefit to us as punishers, only a group benefit that the punisher shares. Cooperation can be directed toward individual benefit, but cooperative activities are also choiceworthy in themselves. We can self-reflect, but we do so frequently in terms of the norms and expectations of our group. Language deepens and enriches all of these activities.

Social learning, the ability to learn from the social environment, is extremely important for humans. Social learning ranges from having one’s attention called to some aspect of the environment (stimulus enhancement) to high fidelity imitation of a model’s behavior. High fidelity imitation, which includes the detailed reproduction of both necessary and unnecessary behaviors, is a pervasive and very distinctive adaptation in humans. In contrast, replicating outcomes with limited attention to specific behaviors is more common in other primates (emulation). As we will see, human sociality is deeply dependent on high fidelity imitation. In recent years, imitation has become recognized as central to defining features of humans such as intelligence, language, and cumulative culture.

The complexity and pervasiveness of human cooperation make it both species typical for humans and unique among animals. Although the scale and intricacy of cooperation vary greatly across time and culture, it is central to human life, making cooperation an important evolutionary topic. In evolutionary theory, cooperation is defined as interactions in which two or more organisms provide benefits for each other (West et al., 2011). These exchanges may or may not be simultaneous, and the benefits can be the same (food for food) or different (food for information). Those who successfully exchange benefits (e.g., food sharing, information sharing, a division of labor) obtain significant fitness advantages (Cosmides & Tooby, 1992).

The frequency of domination, violence, and war among humans can count against the idea that humans are ethical beings. In this chapter, I discuss aggression and hierarchy in the context of social animals’ relationships and groups rather than as topics separate from or antithetical to those relationships. In this opening section, I summarize seven key ways that aggression and hierarchy must be contextualized, and then I provide arguments and evidence for this viewpoint in the remainder of the chapter.

This book is an extended argument for recognizing and embracing the intimate and powerful connections between evolved human nature and the human good. I have framed these links with Aristotle’s function argument, wherein he suggested that a good instance of any being or entity is found in the excellent expression of its nature. The evolutionary perspective allows us to deepen and extend Aristotle’s timeless and very timely ethics in ways he presaged but could not fully foresee. Aristotle’s ethics, in turn, have made it possible to reinterpret and enrich the understanding of our evolution in ways that only come into view when we look at evolution through a eudaimonic lens. I have focused on the social nature of human beings to develop a theory of the good life for human beings with respect to our evolved sociality. Our social nature is not the totality of our nature, but it is an extremely important dimension, and because it is so central, it has profound implications for the good life. I have discussed seven domains of human sociality, but even chapter-length treatments of these topics provide incomplete accounts of these important aspects of human sociality. Yet, if my argument succeeds in demonstrating that these seven domains conform to Aristotle’s function argument and his account of the good life, then that argument can be further elaborated and extended to other aspects of human nature. This reinterpretation is an attempt to bridge human nature, as it is illuminated by evolutionary science, and ethics, as envisioned by Aristotle.

Given the importance of culture in human life, one of the most important questions about an evolutionary account of human nature is how well it can explain culture. Kappeler, Silk, Burkart, and van Schaik (2010) responded to this challenge by describing culture, with its material elements, social institutions, and linguistic bases, as perhaps humanity’s preeminent adaptation. Tomasello et al. (2005) concurred, seeing humans as “the world’s expert at culture” because we not only interact with conspecifics “but engage them in complex collaborative activities” (p. 675). Evolutionary scientists argue against the longstanding idea that biology and culture are mutually exclusive explanations for behavior because the human capacity for culture is dependent on our evolved cognitive architecture. From this point of view, cultural variation is not a refutation of a universal human nature. Rather, it is an expression of important, species-defining aspects of that nature. Although evolutionary scientists argue for a single human cognitive architecture for culture, this capacity is expressed in an incredible variety of cultural forms because cognitive architecture enables culture but does not dictate its content. I begin by discussing the adaptations that made culture possible to set the stage for an argument about how culture reveals goods that are essential for human flourishing.

One of the fascinating questions about human beings is why we evolved such a strong capacity for individual identity. Identity is usually seen as an aspect of the individual’s separateness and autonomy, but it appears that identity evolved as part of our ultrasocial nature. In this chapter, I describe the intersubjective origin and functioning of individual identity, focusing on four key aspects. My emphasis is on the social ontogeny of individual identity and the complementary recognition of others’ identity and mental activity. First, identity is socially constituted in the richly synchronous interactive world of the infant. Infants only gradually come to recognize themselves as separate individuals who have authorship of their actions. A consciousness of oneself only emerges in relatively large-brained, intensely social species, suggesting that individual identity makes it possible for individuals to function and prosper in highly social environments. The emergence of individual identity can only occur in an interpersonal context because having an identity is a matter of differentiating oneself from others.

Rapidly growing scholarly and popular literatures explore the confluence of evolutionary theory and human morality, seeking a plausible theory of natural ethics. Given the centrality of ethics to this project, it is surprising how rarely evolutionary thinkers clearly define ethics, much less engage a systematic theory of ethics. This is partly due to a deep commitment among these authors to an empirical path to knowledge. In the belief that a good account of ethics has to grow out of the data, they gather elements of ethics from evolutionary accounts of behaviors such as cooperation and helping and attempt to stitch together an evolutionary theory of ethics. Although this approach has some merit, it is no surprise that it has not resulted in a satisfyingly coherent and systematic theory of natural ethics.

The centrality of the social world in human life is nowhere clearer than in the extreme dependence of children on their caregivers. Infants not only require that their caregivers provide for all of their physical needs, they also need a deep affective bond to learn about their physical and social world—to be able to explore, form relationships with others, to act both independently and collaboratively. This bond also scaffolds learning about language, how to interpret others’ behavior, and how to pursue joint projects. Human sociality generally begins with the infant-caregiver relationship. Like so many features of human life, attachment has both continuities and discontinuities with other animals. The extreme evolutionary investment that our species has made in the capacity to learn complex interactions with the physical and social world is evident in the prolonged dependence of human offspring. Even in the simplest forms of human life, children do not produce more than they consume until their late teens. The human investment of relational resources in complex capacities begins with the caregiver-infant relationship, which ramifies throughout individual and collective lives.

Aristotle’s function argument stipulated that human flourishing is a matter of expressing human nature excellently. The purpose of this chapter is to describe the evolutionary approach to understanding human nature. I outline the key premises and practices of the major disciplines that contribute to our understanding of human evolution, which explains the specific nature that characterizes our species. These disciplines include evolutionary psychology, anthropology, ethology, archeology, primatology, comparative biology, game theory, and neuropsychology. Obviously, I cannot cover this disciplinary breadth with great depth in this chapter, but it is important to provide an explanation of the key aspects of the theory and research so that the discussion of the specific findings about human evolution in Part II is more comprehensible to the non-specialist. For those with a strong background in the theory and research on human evolution, this chapter is unnecessary.