According to a prominent tradition of Western thinking, morality is a thin overlay covering human savagery. Human beings are bestial by nature and ethical codes are curbs on their brutish instincts that enable them to live together in relative peace. Morality is a restraint on natural human behavior. At the same time it is believed to be uniquely human. Only humans possess the intellectual powers that are needed to repress natural impulses, and so only they can be moral.

Though this view can be found in many schools of thought, secular as well as religious, it is hard to spell out in any coherent fashion. If morality is a system of rules for the suppression of beastly behavior, where does it come from, and why have humans accepted it? How was it devised and imposed? Such questions are not easily answered, but when morality is assessed as it often is today according to some versions of Darwinian theory, the notion that it is a human construction without roots in our animal nature faces difficulties that are insoluble. If Darwinian theory is sound, morality in humans results at least in some part from evolutionary processes, and when they act as moral beings humans are displaying capacities they have in common with some other animals. Rather than suppressing their instincts, they are behaving naturally.

To view morality as a fetter on animal instincts is to think of it in pre-Darwinian terms, but curiously some of the most ardent Darwinians have also seen it in this way. As a result of his indefatigable defense of Darwinian theory the British biologist T.H. Huxley was known as “Darwin’s bulldog,” but he held that moral life was a struggle to combat nature—a view that left morality hanging in mid-air, without any evolutionary explanation, as a kind of human protest against the cosmos. In our own time Richard Dawkins has reaffirmed the Huxleyan position, concluding his book The Selfish Gene with the declaration: “We, alone on earth, can rebel against the tyranny of the selfish replicators.”1 A problem with this view is that it assumes a discontinuity between the biologies of humans and other animals that Darwin did not recognize. As Darwin wrote:

Any animal whatever, endowed with well-marked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well developed or nearly as well developed, as in man.2

Darwin accepted that humans have a natural capacity for morality that has precursors in other animals. For example, he argued that the social instincts that form the “prime principle” of man’s moral sense can be found in monkeys, pelicans, and dogs, among other animals. Huxley rejected Darwin’s view and so it seems does Dawkins; in doing this they are in line with much modern philosophy in which there is a widespread resistance to any attempt to link moral behavior in humans with the behavior of other animal species. Kant believed that behaving morally means acting in accordance with principles that can be consciously articulated, and many philosophers have thought that because nonhuman animals lack the cognitive and linguistic abilities required for this kind of autonomy they could not be moral beings. A different objection to the idea that morality is natural comes from relativists and postmodernists who argue that morality is a human construction whose content varies widely across different human groups, and who often reject any idea of a fixed or constant human nature.

The idea that morality is uniquely human has many variations, but all of them rest on the assumption that humans are in some fundamental way exempt from the evolutionary laws that govern other animals. Darwin’s theory of natural selection does not entail any strong type of genetic determinism regarding human behavior, and attempts to apply evolutionary models to the development of cultures have not been notably productive.3 Even so, the assumption that human moral behavior has no roots in traits we share with our closer evolutionary kin is hard to square with any version of Darwin’s theory. It is difficult to resist the suspicion that this assumption is an inheritance from religion, and it is notable that much of the debate surrounding evolution and ethics assumes a view of morality derived from Western traditions of monotheism (to which Islam in this respect belongs). In these traditions the core of morality is a set of rules, laying down duties, imposing prohibitions, and specifying what is permissible; and a necessary part of being a moral “agent”—someone who acts morally—is engaging in deliberation using principles that apply to everyone.

A different view prevailed among the Greeks, for whom the core of ethics was the virtues. Rather than acting in conformity to principles, they believed, good human beings tend to live according to right action. And while deliberation might at times be necessary, morality was essentially a habit of good judgment and behavior. Acting well meant displaying courage or prudence, for example, rather than obeying rules or principles. The type of reasoning associated with this Greek view was more casuistic, a case-by-case approach in which the situations in which actions were taken were extremely important. Greek ethics was not normally relativistic—Aristotle took for granted that courage and prudence are generically human virtues—but it did not aim to formulate universal rules.


Western thinking contains both of these conceptions. In one morality is modeled on law and has at its center a set of categorical demands, while in the other morality is based on precepts for living the good life and has more in common with medicine, hygiene, and the practical arts, such as building and gardening. These conceptions have often been combined in central Western traditions. Medieval Christian thinkers accepted that the virtues were an integral part of moral life, and adopted from the Greeks the view that prudence and fortitude, for example, were among them. Again, obeying legitimate moral rules has always been seen as virtuous. Yet there remains a basic difference between the view that moral behavior means acting on principles and the Greek idea that it means having good habits and dispositions, and it has been the former view that has been accepted by most modern philosophers.

In Moral Minds, Marc Hauser, a psychologist at Harvard who has studied social behavior and altruism among monkeys, accepts the prevailing view that moral behavior is fundamentally about conforming to principles, but argues that this view attaches too much importance to conscious processes of reasoning. Just because we reason from explicit principles—handed down from parents, teachers, lawyers, judges, or religious leaders—to judgments of right and wrong doesn’t mean that these principles are the source of our moral decisions. On the contrary, Hauser argues that moral judgments are mediated by an unconscious process, a hidden moral grammar that evaluates the causes and consequences of our own and others’ actions.

Viewing human moral psychology with reference to an instinct or faculty we share with some other animals, Hauser rejects the idea that we must be able to articulate the reasons for our actions in order to be moral agents. In his view both moral judgment and behavior are largely the product of unconscious processes—not the repressed thoughts and desires of Freudian theory but the vast areas of mental life that lie beyond the reach of conscious awareness. Though they are widely accepted, accounts of morality in which conscious deliberation is central are, according to Hauser, unreal. Hauser is not denying that moral reasoning is employed in many areas of life—as when judges reach opinions, or teachers give out grades. Rather, he is arguing that when people deliberate and make decisions in such contexts they cannot help relying to some extent on processes of thought that need not be based on, and often are not fully accessible to, conscious awareness.

A rich, pathbreaking book, Moral Minds uses evidence from rapidly advancing research on animal and human behavior to suggest that humans have an inborn moral faculty, parts of which they share with other animals—a claim that is acutely relevant to some of the most fundamental contemporary debates in philosophy and public life. Hauser ranges widely over a variety of disciplines, supporting the idea of innate moral knowledge by citing, for example, findings by the neuroscientist Antonio Damasio that patients with damage to their frontal lobes nevertheless “distinguished between morally permissible and forbidden actions and justified them at an advanced, adult level.” He also invokes Frans de Waal’s Chimpanzee Politics4 to illustrate the capacity of nonhuman primates to make judgments about harm and consequences of the kind that are central in morality.

As Hauser acknowledges, the idea of an innate moral faculty or sense is not new, and was common among the thinkers of the Scottish Enlightenment, including David Hume. For Hume morality was based in the natural emotion of sympathy or benevolence while justice was an “artificial virtue,” a system of conventions that has developed because benevolence is limited and humans live in conditions of moderate scarcity. Once conventions of justice are established, human beings use their powers of reason in applying them; but these conventions develop as unintended consequences of social interaction over time rather than as a result of any process of reasoning, and are mostly accepted as a matter of habit. “Mankind is an inventive species,” Hume writes, and though the rules of justice seem natural “if by natural we understand what is common to any species, or even if we confine it to mean what is inseparable from the species,” they come into being “without the intervention of thought or reflection.”


In Hume’s view our judgments of right and wrong reflect the kind of species humans are, with dispositions for sympathy and pleasure and a capacity for approval and disapproval of one another’s character and actions. Using our moral sense involves employing these abilities, and in the case of the natural virtues—which include prudence and benevolence as well as qualities like self-esteem—includes having the appropriate emotional responses in circumstances where these virtues may be required. Hume did not deny that acting prudently or benevolently requires thought and judgment; but it does not presuppose the application of rules, only the intelligent use of natural human capacities.

Hauser links his account of a moral faculty with both Noam Chomsky’s theory of a universal human grammar and John Rawls’s theory of justice as fairness. Chomsky’s hypothesis that language use is governed by innate rules has made a major impact on linguistics, psychology, and cultural anthropology; but the content of these rules and the degree to which they vary between cultures are disputed, and the idea of a universal grammar remains controversial. Linking the idea of innate morality to such an ambitious and contested theory of language acquisition burdens it with a considerable baggage that does not clarify the origins of moral judgment. More fundamentally, thinking of the moral faculty as strictly analogous to a universal grammar reproduces the model of morality Hauser rightly finds inadequate. The core of Chomsky’s theory is the claim that there are universal rules of language use that are innately human. As Hauser puts it:

The language faculty maintains a repository of principles for growing a language, any language. When linguists refer to these principles as the speaker’s grammar, they mean the rules or operations that allow any normally developing human to unconsciously generate and comprehend a limitless range of well-formed sentences in their native language. When linguists refer to universal grammar, they are referring to a theory about the set of all principles available to each child for acquiring any specific language.

Before the child is born, she doesn’t know which language she will meet; and she may even meet two if she is born in a bilingual family. But she doesn’t need to know. What she does know, in an unconscious sense, is the set of principles for all the world’s languages—dead ones, living ones, and those not yet conceived. The environment feeds her the particular sound patterns of the native language, thereby turning on the specific principles of only one language, or two if the parents are bilingual. The problem of language acquisition is therefore like setting switches. Each child starts out with all possible switches, but with no particular settings; the environment then sets them according to the child’s native language.

Just as a universal grammar contains linguistic universals embodied in rules of language use, so, it has been argued, there are moral universals, which are embodied in an inborn set of moral rules. Throughout Moral Minds, however, Hauser is emphatic that he does not accept a single set of rules about morality and that his is “a pluralistic position, one that recognizes different moral systems, and sees adherence to a single system as oppressive.” Even so he is insistent that human moral capacities embody universal principles. While he rejects the view that “puts precise moral rules or norms in the newborn’s head,” he also rejects the idea that the human moral faculty lacks any rules:

We are born with abstract rules or principles, with nurture entering the picture to set the parameters and guide us toward the acquisition of particular moral systems. This middle view is the one I favor. It comes closest to the linguistic analogy. It makes the obvious point that something about the human brain allows us to acquire a system of moral norms. And it makes the equally obvious point that dogs and cats that grow up with humans never acquire our moral norms.

Though he does not aim to settle the question definitively, Hauser suggests that the part of the moral faculty that is unique to humans is that which they use “to create judgments of permissible, obligatory, and forbidden actions.”

The problem with this argument is not its suggestion that the human moral faculty has unique features, which can hardly be doubted. It is that it takes for granted that these have to do with creating and following rational rules or principles. Here Hauser differs from Hume, who believed that when we employ our moral sense we pick out discrete qualities of vice and virtue. So, for example, when we judge whether an action is benevolent—such as an act of generosity—Hume argues that we feel a pleasurable emotion regarding it, which reflects our sentiments regarding the traits of character such actions express. These sentiments in turn, Hume believed, reflect the usefulness of the character traits to those who possess them and to society in general.

No doubt there are many difficulties with this account, including those that arise when we try to clarify the idea of usefulness. Yet Hume’s view that morality is based in natural human capacities for sentiment and judgment is more plausible, it seems to me, than views in which reasoning from principles is fundamental, because it fits better with an evolutionary account of the origins of morality. As Hume put it in a chapter of his Treatise of Human Nature entitled “Of the Reason of Animals,” “When any hypothesis…is advanc’d to explain a mental operation, which is common to men and beasts, we must apply the same hypothesis to both.”5 In Hume’s account, as in recent evolutionary accounts, human morality develops out of, and remains dependent on, capacities and traits that humans share with their closer evolutionary kin and there is no unbridgeable discontinuity between the two. Applying principles remains a distinctive feature of moral life, but one that reflects human conventions rather than rules of conduct hardwired in the human brain.

In presupposing that the innate content of morality must be a set of principles—however abstract and culturally variable—Hauser departs from the account of the moral sense presented by Hume. He does so partly under the influence of John Rawls. He writes:

Like the British philosophers of the Enlightenment, especially David Hume, Rawls believed in a moral sense, a sense of justice that was designed on the basis of principles that “determine a proper balance between competing claims to the advantages of social life.”

However, pairing Hume and Rawls in this way blurs significant differences. For Hume, following rules is a central part of morality only where justice is concerned, and even there he was ready to make exceptions to the rules where such exceptions promote the general welfare. For example, he supported the forcible recruitment of seamen by “press gangs” that was practiced under the authority of the British crown for centuries. In contrast, while he made use of Hume’s account of the circumstances in which justice develops, Rawls viewed justice in Kantian terms as “the first virtue of social institutions” and viewed acting in conformity with its principles as an integral part of being a moral agent. While for Rawls (and Hauser) universal principles generate intuitions about which actions are morally right or wrong prior to generating any emotions, for Hume emotions precede our moral judgments.

By using the theories of Chomsky and Rawls to model the moral faculty, Hauser links his account with an understanding of morality that in other respects he rightly resists. Despite rejecting the view that having the ability to articulate principles is an essential part of acting morally, he endorses the belief, entrenched in Western religion and reproduced in philosophy by Kant and Rawls, according to which morality means acting on rational principles. In doing so he accepts an understanding of what it is to be moral that is culture-specific, and one that has not always been accepted, even in Western traditions.

One of the chief obstacles to a naturalistic view of ethics—meaning here not any view that conflates facts with values but instead the belief that morality must be explained according to natural human capacities and traits—has been the belief that human nature is amoral or savage. A strong version of this view, which Frans de Waal, a professor of primate behavior at Emory University, has usefully described as Veneer Theory, was invoked by Hobbes when he described a state of nature as a condition in which homo homini lupus—“man is wolf to man.” As de Waal observes, this is unfair to wolves, which are among the most gregarious and cooperative of animals, while it denies the fact of natural human sociability.

De Waal is one of the world’s foremost authorities on nonhuman primates, and his thoughtful contribution to Primates and Philosophers is enriched by decades of close observation of their behavior. Using this evidence and research conducted by other primate scientists, he criticizes the understanding of morality predominant among contemporary moral philosophers, who he believes for the most part accept versions of the Veneer Theory. He argues that humans are like their closest evolutionary kin in being moral by nature. For example, he cites some fascinating evidence showing that monkeys, like humans, have a marked aversion to inequity.6

Along with a wealth of rigorous research de Waal includes some lovely anecdotes. He cites a report of a female bonobo who had captured a starling and been urged by her keeper to let it go; she climbed to the highest point of the highest tree in her enclosure, carefully unfolded the bird’s wings, and spread them wide open before trying to throw it out of the enclosure. When the bird fell short, the bonobo guarded it for a long period against a curious juvenile bonobo.

As de Waal comments, the bonobo displayed a capacity for empathy and even exercised it across species boundaries: she had a notion of what was good for the bird, and did her best to achieve it. Of course there will be many who reject this interpretation as anthropomorphism, and it is true that we should avoid projecting distinctively human traits onto other species. It is wrong to describe a cat playing with a mouse in terms that invoke human sadism, or group hunting among lions as a type of warfare. Again, though they may have antecedents in the behavior of other primates, torture and genocide remain peculiarly human. Anthropomorphism should be avoided in these and other contexts.

But the larger danger lies surely in what de Waal has termed anthropodenial—the a priori rejection of shared characteristics between humans and animals, “which leads to a willful blindness to the human-like characteristics of animals, or the animal-like characteristics of ourselves.” What justification can there be—apart from a religious faith in human uniqueness—for rejecting evidence that points to the animal origins of human morality?

Part of the resistance to de Waal’s argument seems to come from a sense that it deflates morality. Many philosophers have argued that without awareness of the principles it expresses, altruistic or empathetic behavior is no more than a repertory of emotional responses; but this presumes what has yet to be shown, that acting according to our natural sentiments cannot be fully moral. All the commentators in Primates and Philosophers—an impressively well-focused collection of essays, the longest of which is drawn from the Tanner Lectures delivered by de Waal at Princeton’s Center for Human Values in 2004—insist on the essential role of self-consciousness: “genuine” morality requires something like Kantian autonomy—being responsible for one’s actions and capable of specifying the reasons on which they are based—that confines it to humans. The philosopher Philip Kitcher maintains that unless they include a high level of rationality and self-consciousness, expressions of altruism that are based on sympathy “fall a long way short of morality.” Christine Korsgaard presents a version of the same view when she contends that morality only emerges along with a form of self-consciousness that allows agents to know the grounds or reasons for their beliefs and actions—a type of self-awareness only humans possess. Defending a modified version of de Waal’s Veneer Theory, Robert Wright maintains that reciprocal altruism of the kind to which de Waal and other students of animal behavior refer is not “true morality” because it cannot be universalized.

Peter Singer uses his contribution to Primates and Philosophers to restate the argument for equal moral consideration for animals for which he is justly celebrated. In his substantive moral theory Singer is a utilitarian in the tradition of Hume and Jeremy Bentham, but his belief that morality is based on impartial principles aligns him with Kant rather than Hume. Singer shares with Kant the view that the test of right action is whether it conforms to universal principles—a view in line with that defended by most other contemporary philosophers, who insist that morality is a human prerogative. Singer’s stand on animal rights is, in effect, an application of this view to other species. While he argues in favor of extending the scope of moral concern beyond humans, he does so by invoking a conception of morality that is anthropocentric. In each case we see an a priori move of the sort against which de Waal has warned, which responds to evidence of sympathy and reciprocity in other animals not by revising the received view of morality but by reasserting the parts of it that exclude other species.

Many philosophers have accepted an understanding of morality that is difficult to square with the findings of science, and even to state coherently. Such is the view that Hauser and de Waal have incisively criticized: while humans are fundamentally amoral or bad, morality is uniquely human. Hauser’s and de Waal’s research suggests something more like the Greek standpoint, of a more practical, virtue-based morality, which accepted that humans are moral by nature.

An evolutionary view is bound to be more pluralistic than that of Greek philosophers such as Aristotle, however. Aristotle’s theory of morality was based on a metaphysical theory of biology, according to which each kind of organism had a natural end-state or goal. Darwinian theories have no place for teleological explanations—that is to say, explanations that rely on ascribing purposes to evolutionary processes.

These processes have no overall purpose or direction. If they have produced an innate moral faculty in humans it is likely sometimes to conflict with other instincts and to leave many moral dilemmas unresolved. The hardest of these dilemmas will not resemble difficulties in grammar, when there is doubt about the right application of a rule. They will be cases where universal human virtues or values point in different directions—as when justice clashes with mercy, or the promotion of general welfare collides with some conception of justice. Evolutionary theories may do much to illuminate the origins of morality, but they are unlikely to help us solve these dilemmas.

This Issue

May 10, 2007