aul Gauguin’s most famous painting shows several human figures set in a Tahitian landscape. They display the human life cycle from infancy to adulthood to old age. One corner of the painting has three questions: Where do we come from? What are we? Where are we going?

To answer these fundamental questions, Edward O. Wilson’s new book suggests, we need to unify all our knowledge of nature by combining the natural sciences, the social sciences, and the humanities. Traditionally, we have looked to religion, philosophy, or the creative arts to answer these great questions. Wilson, a Pulitzer Prize-winning biologist and Harvard professor emeritus, argues that these three ways to understand the human condition have failed. This leaves science—in its quest for a complete knowledge of nature—as the only way to understand the human story.

Wilson separates philosophy from science, because he assumes that philosophy must rely purely on introspection and logic without scientists’ empirical research. In doing so he turns away from the position he took in an earlier book, Consilience: The Unity of Knowledge (1998), which argued that the search for the unification of all knowledge of nature began in Greek antiquity with Thales of Miletus and Aristotle. Aristotle saw moral and political philosophy as a biological science, and what we call “natural science” was for centuries described as “natural philosophy.” Wilson acknowledged the force of this disposition in Consilience, identifying his biological science of ethics and politics as an extension of the empiricism of Aristotle, David Hume, and Charles Darwin, as opposed to the transcendentalist tradition of Plato, Immanuel Kant, and John Rawls.

If Wilson’s project for a Darwinian unification of knowledge is to succeed, it must revive that Aristotelian tradition of natural philosophy. Darwin himself adopted ideas from David Hume and Adam Smith about the natural moral sentiments. Even the concept of the evolutionary emergence of life as an unintended order was derived from Smith and other Scottish philosophers.

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Recently, evolutionary moral psychologists, such as Jonathan Haidt, have recognized they are reviving the empiricist moral philosophy of Aristotle and Hume. Some contemporary philosophers have embraced “experimental philosophy” as a way of putting their ideas to the test of empirical scientific research. A few political scientists have begun to argue that their science needs to become a biopolitical science of political animals. All of this contributes to a modern renewal of the ancient quest for a philosophical science of nature through a Darwinian natural philosophy. We must wonder, however, whether such a Darwinian natural philosophy is inherently—and fatally—reductionist and nihilist.

Wilson’s reductionism is suggested by his statement in Consilience about reducing all knowledge to physics: “all tangible phenomena, from the birth of stars to the working of social institutions, are based on material processes that are ultimately reducible, however long and tortuous the sequences, to the laws of physics.” This strong reductionism is so implausible that even Wilson cannot consistently embrace it. In most of Consilience, he actually rejected “physics envy,” and he insisted that biologists must “inevitably encounter emergence, the appearance of complex phenomena not predictable from the basic elements and processes alone.” He identified human beings as “emergent animals” who have capacities that are constrained, but not specifically determined by the laws of physics. In The Social Conquest of Earth, Wilson never argues for reducing everything to the laws of physics, and he implicitly endorses the idea of the irreducibly emergent traits of life.

Biologists recognize emergent phenomena as those complex wholes with properties we could not explain or predict from our knowledge of the parts. The emergence of novelty occurs throughout the evolution of the universe. Passing through levels of complexity, new properties emerge at higher levels not fully reducible to lower ones. When chemicals in the early universe formed the first living cells, that was emergence. When the first multi-cellular organism arose, that was emergence. When the human mind arose from the evolution of the primate brain passing over a critical threshold of size and complexity, that was emergence.

Although the human mind is constrained by the laws of physics and chemistry, we cannot fully explain or precisely predict the workings of that mind through the laws of physics and chemistry. One ground for emergent complexity in Wilson’s science is genetic plasticity, the idea that genes allow for a wide but still constrained flexibility in response to the cultural and individual contingencies of life. Our human genetic nature constrains but does not determine our cultural traditions and individual judgments.

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How does the coevolution of genes, culture, and judgment explain human morality and politics? Some critics of Wilson’s project worry that any evolutionary account of morality and politics must deny that there can be any objective or fixed standards of right and wrong, which is tantamount to nihilism.

Is Darwinism nihilism? If you are a Platonist, yes. If you are not a Platonist, no. Most Platonists today are disappointed Platonists—people with unfulfilled Platonic expectations. Accepting Darwinian evolution as true, they believe all living forms have evolved, which means they cannot possibly conform to Plato’s intelligible realm of eternal Ideas. If everything has evolved, this must include moral and political order, and thus there is no eternally unchanging Idea of the Good by which we can see absolute standards of right and wrong. Consequently, there are no moral absolutes, and we must accept moral relativism or nihilism. Darwinism is “true but deadly,” as Nietzsche said. Thus do these disappointed Platonists become nihilists.

But if you do not have Platonic expectations, you will not be disappointed by the Darwinian conclusion that everything has evolved, and therefore human beings have evolved. Without the Platonic assumption that morality must be grounded in a moral cosmology, you will be satisfied with a Darwinian explanation of morality grounded in a moral anthropology. Even if morality has no eternal grounding in a cosmic God, a cosmic Nature, or a cosmic Reason, human morality still has an evolutionary grounding in human nature, human culture, and human judgment. You can say, with Leo Strauss, that “however indifferent to moral distinctions the cosmic order may be thought to be, human nature, as distinguished from nature in general, may very well be the basis of such distinctions.” And thus in contrast to the disappointed Platonists, the satisfied Darwinians are not nihilists.

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Satisfied Darwinians like Wilson see at least four mechanisms for the evolution of social cooperation and human morality: kin selection (cooperating with relatives), direct reciprocity (tit-for-tat exchanges), indirect reciprocity (having a good or bad reputation), and multilevel selection (individual selection and group selection). The most controversial part of Wilson’s new book is that while he had previously embraced kin selection theory, he now argues against it. Kin selection is the idea that animals have evolved to serve not only their personal fitness (the number of their surviving offspring) but also their inclusive fitness (including the fitness of their collateral relatives), and consequently animals tend to be altruistic towards closely related kin with whom they share genes. Wilson argues that as long as multilevel natural selection works generally to explain social evolution, there is no need for a theory of kin selection.

But multilevel selection theory is not an alternative to kin selection theory. Rather, they complement one another. Kin selection cannot be the whole story, because we need to explain how unrelated individuals can cooperate. But kin selection must be part of the story, because we need to explain why individuals tend to cooperate with close relatives more reliably and productively than with distant relatives or strangers. This idea was developed by Aristotle: the natural sociality of animals originates as an extension of parental care and membership in ever wider groups. Aristotle also saw that this natural sociality reached its peak among the social insects and human beings, and thus again Aristotle anticipated Wilson.

In Sociobiology (1975), the book that brought him fame, Wilson identified four pinnacles of social evolution: the colonial invertebrates (such as the corals, the Portuguese man-of-war, and sponges), the eusocial insects (ants, bees, wasps, and termites), nonhuman mammals, and humans. Although this sequence seems to move from more primitive to more complex forms of life, it also moves from more cohesive or cooperative societies to more discordant or competitive societies. Colonial invertebrates can be seen as “perfect societies,” because colonies consist of genetically identical individuals, and consequently they show absolutely altruistic cooperation. But with sexually reproducing organisms, no two individuals are genetically identical, which creates conflicts of interest even among related individuals.

In The Social Conquest of Earth, Wilson moves from four pinnacles of social evolution to two. He identifies two paths to the social conquest of the earth—the insect path and the human path. The social insects rule the invertebrate land environment. Humans rule the vertebrate land environment. Like the social insects, humans are “eusocial” in the technical sense that multiple generations of individuals live together, caring for dependent offspring and cooperating in a social division of labor. Social insects organize their colonies largely through pure instinct, with the insect queen producing robotic offspring. Humans, however, must organize the cooperation of individuals through personal relationships based on social intelligence, which requires a constantly readjusted balance between the selfish interests of individuals and the social interests of groups. Wilson explains this tense balance in human social life as exhibiting the countervailing evolutionary forces of individual selection and group selection.

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The unsteady balance between the individual and the group in human societies constitutes what Wilson identifies as the “iron rule” of social and moral evolution:

selfish individuals beat altruistic individuals, while groups of altruists beat groups of selfish individuals. The victory can never be complete; the balance of selection pressures cannot move to either extreme. If individual selection were to dominate, societies would dissolve. If group selection were to dominate, human groups would come to resemble ant colonies.

So if we ask whether human beings are innately good or innately evil, we should answer that they are both. And for that reason, “[h]uman beings and their social orders are intrinsically imperfectible.” Here is the scientific basis for the tragic realism of evolutionary ethics.

The ultimate mechanisms of moral evolution are enforced through the proximate mechanisms of moral emotions. For example, Wilson identifies the human sense of honor as crucial for moral experience. This sense of honor includes the moral emotions of indignation and resentment in response to injustice. This sense of injustice might express what Strauss called “those simple experiences regarding right and wrong which are at the bottom of the philosophic contention that there is a natural right.” It is this that allows us to derive rights from wrongs: our moral history is a history of resistance to injustice from which we derive standards of fair treatment.

But if those “simple experiences regarding right and wrong” are the purely human experiences of an animal species shaped by evolutionary history, and if that evolved human species is enduring but not eternal, do those experiences support the philosophic claim that there is a natural right? The Darwinian natural philosopher says yes.