The Science of the Evolution of Morality

Doug Mann

Since Charles Darwin published The Descent of Man, his second major book about evolution, in 1871, researchers have made many discoveries that flesh out Darwin’s little-known ideas about the evolution of morality. Recent papers in Free Inquiry by Ronald Lindsay and James Hughes have touched briefly on the evolution of morality, but there’s much more to this important story. In this article, I will review key steps in the evolution of morality during three phases of the evolution of life on Earth and discuss implications for organized religion and its relationship to morality.

Darwin knew that his theory of evolution by natural selection faced several daunting explanatory challenges to be understood and accepted by scientists and the public. For example, in On the Origin of Species, published in 1859, Darwin described a general process for the seemingly improbable evolution of “organs of extreme perfection,” such as the human eye, whereby simple forms of the evolving eye might provide a benefit to survival. Darwin knew of few intermediate forms to list in support of his explanation, but he was right; scientists have since discovered a series of steps representing the evolution of the eye in a variety of current species, from simple light-sensitive spots, to spots within cups, to cups partially closed to form a “pinhole camera” proto-eye, to eyes with very simple lenses, and so forth.

The story of the intuitively improbable evolution of human morality is analogous to the story of the evolution of the eye, in that science has subsequently discovered many intermediate steps that flesh out Darwin’s broad but conceptually correct view of the origins of morality. In The Descent of Man, Darwin provided a general description of how morality evolved, with the advantageous foundations of morality emerging in social animals, in particular among our primate ancestors. Darwin’s explanation—and subsequent scientific discoveries—show that morality is not a mysterious exception to evolutionary theory that required supernatural intervention to emerge, as claimed by proponents of “theistic evolution.” In contrast to such supernaturalism, a naturalistic view of the theory of evolution helps us to see the parallels and the high degree of continuity between our species and others.

The evolution of human morality is entirely explained by the competitive and reproductive advantages of a highly structured, cooperative social life within groups whose members are of the same species. Humans represent one of only about twenty small branches of the vast evolutionary tree of life that display particularly high levels of social organization. When did this advantageous but rare level of social organization first appear in the evolutionary history of life on Earth, prior to the recent evolution of our own species? And how is the emergence of a high level of social organization in humans intertwined with the evolution of morality?

During each phase of the evolution of life on Earth, individual hereditary variations that influenced social behavior encountered a variety of environmental and social selection forces. In primates, the most successful behavioral variations in terms of survival and reproduction slowly strengthened and eventually resulted in the remarkable self-domestication of our species, shaping our minds and bodies and producing powerful traits such as empathy, reciprocity (a desire to exchange and repay favors), and the strong desire for social affinity and the approval of others. This process of evolutionary self-domestication culminated in the individual prosocial traits and cultural rules of behavior that we refer to as “morality.” This story begins with the evolution of life on Earth almost four billion years ago and moves forward in three distinct phases, culminating in the emergence of human sociality and morality as they exist today.

The First Phase: The Slow Genetic Evolution of High Sociality and Pre-Moral Traits

In On the Origin of Species, Darwin summarized the theory of evolution by natural selection as follows:

As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

The advantages of a cooperative, highly organized social life to help a species succeed “under the complex and sometimes varying conditions of life” are many, but there was no guarantee that the process of evolution by natural selection would result in any particular social structure emerging among the diverse forms of life that gradually evolved. It’s now understood that Darwin’s “strong principle of inheritance” is made possible by genes carried on strands of DNA, and that random errors occurring in the DNA copying process may make an organism “vary however slightly in any manner profitable to itself.” However, the small hereditary variations that prove to be advantageous typically take a very long time and a multitude of generations to result in significant changes to a species. Life first appeared on the Earth about four billion years ago, and a full 3.8 billion years, or 95 percent of the evolutionary history of life, would pass before genetic mutations accumulated in a few species in a way that produced a high level of cooperative social organization.

The rise of the social insects: The power of instinctive cooperation

Insects began to appear on Earth about 400 million years ago, but it wasn’t until 150–200 million years ago that the earliest termites and ants evolved. These were the first insects that evolutionary biologists refer to as “eusocial” or “true social” species. These species have a distinctive set of characteristics: the life of a colony is based around a nest where multiple generations of the species live and take care of offspring; there are sharply defined, specialized roles for different subgroups or “castes” of the colony; and sexual reproduction is limited to specialized castes. For example, a colony of ants may have one or more actively reproducing queens in the nest, along with princesses (virgin queens who will mate with drones to establish new colonies), drones (the reproductive males), and sterile workers and soldiers. The characteristics of such species, under the right conditions, produce significant advantages in foraging for food, reproduction, care of offspring, food storage, nest maintenance, and nest defense. This distinctive level of social organization has been highly successful since its emergence. Today, ants and termites represent less than 2 percent of the total number of current insect species, but ants and termites constitute more than half of the worldwide total body weight of living insects.

There are obvious parallels between “true social” insects and the social lives of humans, according to entomologist Edward O. Wilson. Humans often live and work in large, complex hierarchies while conforming to specialized roles and cooperating with large numbers of both familiar people and strangers, and some cultures have even featured types of reproductive caste systems (although not the genetically wired reproductive roles found in the technical definition of a eusocial species). Furthermore, human beings often display considerable levels of altruism and self-sacrifice toward kin, familiar community members, and even strangers.

Although the behavior of “true social” insects foreshadows the evolution of human morality in terms of conformity to social roles that require self-control and self-sacrificing behavior, there are limits to this analogy. Insect behavior is instinctive, with a limited set of hard-wired behaviors made possible by a relatively simple nervous system. Furthermore, the evolution of “true social” insect species is explained by the fact that all the insects in a colony are genetically related to each other, so a self-sacrificial act by a soldier ant benefits the survival and reproduction of the genes the soldier ant carried. (In evolutionary biology, such insect behavior demonstrates “inclusive fitness” and the benefits of “kinship selection” or simply “nepotism.”)

Nevertheless, the “true social” insects illustrate an important truth about morality: the immense advantages of cooperative social life organized around specialized roles can be achieved only through self-control and the altruistic and self-sacrificing behaviors that are also central to human morality. But how did self-control and altruism evolve in organisms with much more complex brains and behavior than those of ants and termites?

Mammals and their helpless offspring: The power of attachment

Mammals begin to appear in the fossil record about 200 million years ago. Hormones such as oxytocin and vasopressin that were important in the reproductive systems of reptiles gained additional functions in the evolution of the “self-care system” in mammals. The self-care system produces feelings of pleasure and comfort when a mammal is well-fed and feelings of pain and stress when a mammal is hungry or threatened.

Warm-blooded mammals have the advantage over cold-blooded reptiles of being able to move and feed at any time of the day or night, but they also require about ten times as much food as a reptile of the same size. High energy needs required problem-solving flexibility in early mammals, and mammalian brains slowly began to enlarge. However, larger brains meant births at early stages of development and, therefore, longer periods of helplessness and dependency in mammalian offspring. According to philosopher Patricia Churchland, it took about seventy million years for the mammalian self-care system to evolve into a robust attachment system between mothers and offspring. The hormones oxytocin and vasopressin play important roles in both the self-care system and the attachment system. The attachment system produces pleasure and feelings of well-being and comfort in the close, nurturing relationship between mothers and offspring and feelings of distress and pain when the other shows signs of distress.

The importance of the evolution of the attachment system in mammals to the eventual evolution of human morality cannot be overstated. The evolution of highly social insects is a powerful demonstration of the benefits of instinctive altruistic and self-sacrificial behavior, but the evolution of the attachment system in mammals was a vital step toward the possibility of high sociality supported by individual altruism and self-sacrifice in much more complex organisms, such as our species. In brief, the attachment system is the biological basis for caring for others that, once firmly established between mothers and offspring, could generalize to mates, kin, and community. The attachment system played an important role in the evolution of pre-moral traits in our closest evolutionary relatives.

Primate bands with dominant leaders: The power of coalitions

About sixty-five million years ago, a mass extinction event contributed to the demise of the dinosaurs, enabling mammals, including the early primates, to evolve freely and spread rapidly. By about eight million years ago, an evolutionary branch emerged that included gorillas, chimpanzees, and the ancestors of Homo sapiens. All the species found in this evolutionary branch have been highly social in nature. Chimpanzees, who—along with bonobos—are our closest genetic relatives, live in loosely organized bands that have a “dominance hierarchy” structure with an alpha male at the top of each band’s social order. However, the alpha male’s power is constrained by coalitions of less powerful chimpanzees. Chimpanzees have a complex social life and engage in problem solving to manage frequent conflicts. They have traits of self-control and deference to authority that Darwin saw as important precursors to morality, according to moral psychologist Dennis Krebs.

The emotional attachment system that evolved between mothers and offspring in earlier mammals also plays an important role in the social lives of bands of chimpanzees, according to primatologist Frans de Waal. Chimpanzees appear to care for others in the band, particularly kin and “friends.” For example, chimpanzees in coalitions groom each other and comfort a coalition member who has been in a fight, accompanied by a rise in oxytocin levels. Chimpanzees appear to sense the emotional states of others in the band and may therefore possess a form of what we call sympathy or empathy in humans. Chimpanzee social life demonstrates the effect of the attachment system when it is generalized to the extended family and others in the band.

Chimpanzees demonstrate at least two other behaviors that are also precursors of morality. Although chimpanzees do not have the sophisticated sense of fairness and justice that humans possess, they do engage in “reciprocity,” where approximately equal favors are exchanged despite a significant time lapse between the first favor and the return favor. For example, chimpanzees are more likely to groom others or share food with those who provided the same or similar favors hours before. Also, chimpanzees are well aware of the implicit rules of behavior in a band. When chimps are caught breaking a rule by an authority figure, they typically stop with minimal protest and take up another activity. Chimpanzees, therefore, possess several traits that are crucial building blocks of morality.

Genus Homo and big brains: The power of social complexity

In The Descent of Man, Darwin held that human morality derives directly from the traits of our primate ancestors and other social animals:

As man is a social animal, it is almost certain that he would inherit a tendency to be faithful to his comrades, and obedient to the leader of his tribe; for these qualities are common to most social animals. He would consequently possess some capacity for self-command. He would from an inherited tendency be willing to defend, in concert with others, his fellow-men; and would be ready to aid them in any way, which did not too greatly interfere with his own welfare or his own strong desires.

Around 2.6 million years ago, several species of primates now classified as genus Homo emerged. Some of these ancestors began to make simple stone hand axes. At the same time, the Pleistocene Epoch began, which included a series of glaciations and warmer periods, requiring our primate ancestors to move and adapt. Over the next 2.4 million years, the brain volume of genus Homo would triple, from about 450cc in the earliest species—the same brain volume found in chimpanzees—to 1350cc in our species, Homo sapiens, in the most rapid evolution of complex tissue in the history of life on Earth.

One well-supported explanation for the rapid evolutionary growth of the brain is the “social brain hypothesis,” which holds that as the size of primate bands grew and social life became correspondingly more complex, much higher demands were placed on primate brains in terms of memory and social skills. Across species of primates, brain volume positively and strongly correlates with average social group size. Among our prehuman ancestors, both potential mates and groups favored individuals who could fit in and cooperate, requiring ever more sophisticated social skills, which in turn selected for the development of larger brains. The traits that helped prehumans to cooperate and conform to roles within groups are the building blocks of morality. They are found in basic form in chimpanzees and were refined and expanded during the evolution of genus Homo.

By about 1.5 million years ago, prehumans were beginning to learn to maintain fires to serve as campsites. With a fire as the focus of a campsite, the campsite became like a nest, with various roles emerging to maintain the fire, care for young, defend the campsite, and gather food, analogous to the nest-based roles of social insects. These specialized roles in prehumans had obvious advantages but also made group life more complex, with greater demands on individuals to learn and conform to multiple roles.

By 400,000 years ago, prehumans had become dependent on methods of foraging (hunting and gathering food) that required cooperation by two or more members of a group, according to psychologist Michael Tomasello. Prehumans in these foraging partnerships developed role expectations and rules, feelings of responsibility for the other partner, and mutual respect. In Tomasello’s “interdependence hypothesis,” this sort of cooperation and teamwork, with clear roles by which partners contributed equally, evaluated each other’s performance, and chose foraging partners accordingly, became the foundation for the strong sense of fairness and justice that would emerge in Homo sapiens. The stage was set for our ancestors to develop, commit to, and enforce rules that applied equally to all members of the group. The emergence of effective groupwide rules was intertwined with three major developments: the emergence of culture about 250,000 years ago, intensive social selection for altruistic behavior, and the evolution of the human conscience.

The Second Phase: Gene-Culture Coevolution and the Emergence of Human Morality

Culture is fundamentally about the creation and transmission of ideas, knowledge, skills, and rules, and therefore it depends on “social learning.” Social learning has two components: 1) the ability to learn by imitation or instruction, coupled with 2) the ability to change and improve what one has learned. Starting at least 2.5 million years ago, some of our ancestors made simple hand axes by flaking stones, but these simple tools were produced without any changes for more than two million years, so production of these tools did not demonstrate the second component of social learning. However, by 250,000 years ago, our ancestors were able to produce a great variety of improved and specialized spear points for hunting and share and build on these skills by demonstration, imitation, and, crucially, by refinement and variation. The development of a sophisticated variety of spear points had a significant impact on subsequent human evolution and, by demonstrating the first clear evidence of social learning, marked the beginning of culture.

The emergence of culture was a novel and momentous development in the evolution of life on Earth. In the words of evolutionary biologist Mark Pagel:

Having culture means we are the only species that acquires the rules of its daily living from the accumulated knowledge of our ancestors rather than from the genes they pass on to us. Our cultures and not our genes supply the solutions we use to survive and prosper in the society of our birth; they provide the instructions for what we eat, how we live, the gods we believe in, the tools we make and use, the language we speak, the people we cooperate with and marry, and whom we may fight or even kill in a war.

To Pagel, we live in “cultural survival vehicles” that protect us but also shape and control us.

Gene-culture coevolution shaped our bodies and brains

Culture was (and still is) such a powerful selection force and influence on human behavior that it had a lasting effect on human bodies and brains. In other words, the powerful interaction between genetic traits and cultural selection forces produced “gene-culture coevolution,” as described by Peter Richerson and Robert Boyd. To build on the previous example, the early cultural development of specialized spear points made large-game hunting possible, which could provide large amounts of high-quality food; however, large game hunting with spears requires more in the way of endurance and coordination than brute strength. Over thousands of generations, reliance on large-game hunting selected for slender bodies with greater endurance and therefore changed the shape and capabilities of our ancestors’ bodies.

Culture accelerated the long process that resulted in the self-domestication of our species. The specific cultural selection forces that eventually produced human morality also changed our ancestors’ brains. In terms of brain structure, culture continued the selection for complex brains capable of managing the increasingly demanding requirements of social life. Sexual selection as well as group enforcement of basic rules of behavior selected for traits of individual self-control and conformity, which are prerequisites for morality as well as for stable, beneficial group life.

Domestication of a species can affect bodies as well as brains. In a recent example of selection favoring domesticated behavior, dog breeders who chose puppies for breeding based on their docile and friendly behavior noticed several unexpected effects on the dogs’ bodies after a few generations of selective breeding: the dogs’ tails became curly, ears were longer, and the faces of adult dogs retained some puppy-like characteristics. Selection for docility had produced neoteny, the persistence of some juvenile physical features in the adult form. Similarly, social selection among our ancestors for strong social skills, for the tendency to form lasting emotional attachments, and for social conformity produced not only larger brains but flatter, more expressive faces with larger eyes.

The familiar illustration of an early primate morphing into an upright modern human in a few steps illustrates the cumulative effects of primate genetic evolution and subsequent gene-culture coevolution that persistently selected for social skills and prosocial traits. The very shapes of our brains, bodies, and faces are a testament to the survival value of high sociality, which requires morality for its full expression.

Hunter-gatherer life shaped morality and produced the human conscience

By 150,000 years ago, and possibly even earlier, members of Homo sapiens were the same as modern humans in general appearance. These ancestors lived in nomadic hunter-gatherer tribes. Thousands of generations of life in these hunter-gatherer tribes strengthened human prosocial traits, accelerated the evolution of language, and formalized the basic moral rules of group living. This manner of life also led to the evolution of the human conscience, according to evolutionary anthropologist Christopher Boehm. A crucial period for the evolution of morality was the late Pleistocene, from 125,000 to 45,000 years ago, when our ancestors, using a sophisticated array of spears and other weapons, became increasingly reliant on the hunting of animals for the largest part of a tribe’s food supply. A successful hunt provided a rich supply of protein and fat, but the results were intermittent and uneven; several hunters might go out for an entire day and only one might return with meat. Equitable sharing of meat from a successful hunt among a tribe’s members became essential for the tribe’s survival.

The necessity of egalitarian meat-sharing was an important crucible for the evolution of morality. Boehm has personally studied or reviewed others’ detailed observations of the social lives of about fifty current nomadic hunter-gatherer tribes that probably live much as their late-Pleistocene ancestors did. These tribes have elaborate mechanisms of social control to promote and enforce egalitarian food-sharing. For example, successful hunters are expected to be humble about their skill; someone not from a successful hunter’s family is assigned to distribute the food evenly throughout the tribe; and the tribe monitors the results of a day’s hunt, gossiping so that any attempted cheating concerning food-sharing is detected quickly and known widely, so that the entire tribe can form a united front to confront a hunter who may be trying to hoard game for himself or his immediate family. Also, tribal elders frequently encourage generosity in terms of food-sharing and other forms of helping.

In other words, these hunter-gatherer tribes require hunters and others to engage in altruism, in that each tribe may contain several unrelated kinship groups; egalitarian food-sharing therefore requires giving food to non-kin with no immediate or specific expectation of a comparable amount of food in return. Every member of a tribe must actively participate in enforcing rules such as food-sharing to suppress “free riders” who, openly (in the case of bullies) or secretly (in the case of cheaters and liars), break rules and undermine the rule-followers and the stability of the tribe’s social order. Cheaters and liars are serious types of “free riders” because they attempt to maintain good reputations, which have many benefits, while breaking important rules. Constant judgmental gossip plays an important moral function in these hunter-gatherer tribes, helping to catch free riders and unify the tribe against them. Free riders are the natural enemies of rule-followers and altruists, and they must be caught and disciplined if the tribe is to survive and social order is to be maintained.

Boehm describes this battle between altruists and free riders and its consequences for the evolution of moral rules and the human conscience among our late Pleistocene ancestors:

… [H]umans began to make use of social control so intensively that individuals who were better at inhibiting their own antisocial tendencies, either through fear of punishment or through absorbing and identifying with their group’s rules, gained superior fitness. [“Fitness” in this context refers to advantages in survival and reproduction, not to physical fitness.] By learning to internalize rules, humankind acquired a conscience … . The rules individuals internalize are the cultural products of groups that gossip moralistically on an ongoing basis. That’s how moral codes originate, stay in place, and are refined.

The moral codes found in studies of hunter-gatherer tribes include the same prohibitions found in the moral codes of all human cultures. According to Boehm, “… all human groups frown upon, make pronouncements against, and punish the following: murder, undue use of authority, cheating that harms group cooperation, major lying, theft, and socially disruptive sexual behavior.”

But there is more to the human conscience than the ability to learn moral rules. Darwin viewed the connection between moral rules and emotions as a central feature of the conscience. He observed that the human moral sense was frequently expressed by blushing with shame when an individual’s violation of a moral rule is discovered by others, but that other animals, including other primates, did not display this visible reaction. Darwin wrote to ask acquaintances from all around the world whether people in the local culture blushed with shame when caught in a violation of a moral rule of behavior. Through this pioneering piece of cross-cultural research, Darwin found that blushing with shame occurred among humans across all cultures.

Darwin had investigated a central feature of the human conscience: a universal connection between well-learned rules of behavior and powerful positive and negative emotions such as moral pride, guilt, and shame. Recent studies of normal American children show that blushing with shame begins at about two years of age. However, studies of psychopaths have shown that although they learn moral rules easily, they have no positive or negative emotional reactions to following or breaking moral rules and therefore break them with impunity. The lack of such emotional connections to moral rules justifies the conclusion that psychopaths lack a conscience.

The human conscience, therefore, has two major components: 1) internalized rules, whereby well-learned moral codes become part of one’s cultural identity; and 2) powerful emotions associated with moral rules, whereby positive emotions such as pride are generated by following rules, and negative emotions such as guilt and shame arise when moral rules are broken.

The human conscience emerged from previously evolved traits. Darwin felt that both social instincts and higher mental capacities were necessary for the evolution of a conscience:

The following proposition seems to me in a high degree probable—namely, that any animal whatever, endowed with well-marked social instincts, the parental and affilial 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.

Darwin’s “parental and affilial affections” depend on our ancient mammalian attachment system to enable individuals to form a deep bond to a culture and a culture’s moral rules. The strong desire for parental approval, with corresponding positive and negative emotions when parents are pleased or displeased, became a strong “affilial” desire for the approval of one’s cultural group; positive and negative emotions attached to internalized moral rules provided an evolutionary means to gain and maintain that approval.

The large brains of Homo sapiens provided individuals with the power to learn and navigate the complex social life of a culture and follow rules well enough to maintain a good moral reputation within the culture of one’s birth. The gradual evolution of language, a product of both genetic and cultural evolution, made the transmission of knowledge, including social rules of behavior, much more efficient. Through thousands of generations of tribal life, cultures rewarded and selected those who learned intricate social and moral rules and emotionally internalized those rules as part of each individual’s cultural identity. Thus, our species domesticated itself, achieving a remarkable degree of social conformity to each culture’s moral rules and practices, through the evolution of the human conscience.

Long before the advent of agriculture about 11,000 years ago, all the core features of human morality were in place within hunter-gatherer tribes. Deeply evolved prosocial traits, including the conscience, helped individuals to follow a tribal culture’s moral rules well enough to maintain social order, despite urges that could cause individuals to engage in deceptive or overt selfish behavior. However, the success of agriculture presented new challenges to human morality in the third phase of its evolution.

The Third Phase: The Recent and Rapid Cultural Evolution of Morality

The emergence of agricultural practices about 11,000 years ago marked the beginning of a rapid increase in both the worldwide human population and the size of settled human communities. The “religious” beliefs of hunter-gatherers were mostly animistic, involving capricious spirits that were uninterested in human moral behavior, along with some burial practices that suggested belief in an afterlife. However, these animistic beliefs were of little help in maintaining social order when communities began to grow beyond the small size of tribal groups that had enabled members to monitor each other’s moral behavior so effectively.

According to psychologist Ara Norenzayan, organized religions that feature supernatural “watchers” that monitor and enforce morality in larger, more anonymous human populations emerged well after the advent of agriculture. The larger the population, the more likely that a culture’s predominant religion features a god that monitors and enforces morality, thus counteracting the weakened role of interpersonal moral monitoring that was sufficient in small hunter-gatherer tribes.

Viewed this way, organized religions featuring supernatural moral watchers are a functional product of cultural evolution but with a complex relationship with morality. On one hand, organized religions helped societies to scale up, codify and teach moral rules, and serve as important markers of cultural identity. On the other hand, organized religions have served as a justification for conflict between different cultures and have accentuated the “us vs. them” side of human tribalism, as described by philosopher Joshua Greene. Furthermore, religious moral rules have been added that have little to do with the essentials of human morality that were established during the hunter-gatherer tribal period of human evolution; these “add-ons” often have to do with notions of what is sacred or profane, which is one of the five or six foundational topics covered by moral systems throughout the world today, according to social psychologist Jonathan Haidt. (For brilliant if profane commentary on organized religion’s accretions to moral rules, watch the brief “Ten Commandments” routine by the late comedian George Carlin; the references include a link.) Furthermore, religion’s function as a means of social control has often been used to oppress women and persecute gay people and other social subgroups.

Why has organized religion been such a mixed bag in its effects on morality? One clue is that the things being transmitted in cultural evolution are human ideas, not human genes. Genetic mutations produce small variations that require many generations to produce significant changes in a species. In contrast, any idea that “sticks” in human minds and gains broad acceptance can become a significant force in cultural evolution, widely affecting human beliefs and behavior, including moral beliefs and practices. Therefore, cultural evolution, although rapid and powerful, is not necessarily very adaptive in terms of human well-being. For example, there are tribes living today in Papua New Guinea in which witchcraft is held to be the explanation for crop success and failure, so neighbors are viewed with suspicion when their crops are conspicuously more successful than those of others, particularly by someone whose own crops failed. These superstitious beliefs, a product of cultural evolution, create an endless cycle of suspicion, accusations, violence, and misery. In addition, within the past five years women have been murdered in several cultures in Papua New Guinea and Africa on suspicion of being witches who have caused illness and death in others. Historically, belief in witchcraft has appeared in a number of Western cultures and religions, often with deadly consequences. The products of cultural evolution, including religious beliefs and associated moral rules and practices, can be harmful to human well-being.

Cultural evolution since the advent of agriculture has produced an estimated ten thousand religions and many corresponding versions and extensions of the central themes of morality. A large majority of these religions are no longer practiced, and just a few highly successful religions and moral codes predominate in today’s world. However, at least in the Western world, religions are rapidly losing their status as essential pillars and arbiters of the morality of society. As noted by Norenzayan and others, several largely nonreligious Scandinavian countries are the happiest, most orderly, and most prosperous countries in the world.


Human morality is a natural phenomenon that beautifully demonstrates the central principles of the theory of evolution by natural selection. The lengthy evolutionary history of morality, which includes both genetic and cultural evolution, explains the unique power of moral rules, in that the human conscience connects deeply evolved traits and emotions to well-learned cultural rules of behavior. Morality made it possible for humans to build and maintain highly complex but generally orderly societies, enabling our self-domesticated, hyper-social species to spread throughout the world. Organized religion, itself a product of cultural evolution, is a latecomer to the evolution of human morality and is demonstrably not essential to social order in today’s world. Secular humanists have every reason to view morality as a deeply evolved and entirely human endeavor that must continue to change and adapt—in a way that is informed by the best of science and reason—for the good of humanity.

Further Reading

  • Boehm, Christopher. Moral Origins: The Evolution of Virtue, Altruism, and Shame. New York: Basic, 2012.
  • Carlin, George. “The Ten Commandments,” Complaints and Grievances. HBO Special, 2001; see
  • Churchland, Patricia. “The Neurobiological Platform for Moral Values,” Behaviour 151 No. 2–3 (2014).
  • Darwin, Charles. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London: Murray, 1859.
  • ———. The Descent of Man, and Selection in Relation to Sex. London: Murray, 1871.
  • Greene, Joshua. Moral Tribes: Emotion, Reason, and the Gap between Us and Them. New York: Penguin, 2013.
  • Haidt, Jonathan. The Righteous Mind: Why Good People Are Divided by Politics and Religion. New York: Pantheon, 2012.
  • Hughes, James J. “Enhancing Virtues: Fairness,” Free Inquiry 37:3 (2017).
  • Krebs, Dennis. The Origins of Morality: An Evolutionary Account. New York: Oxford, 2011.
  • Lindsay, Ronald. “How Morality Has the Objectivity that Matters—Without God,” Free Inquiry 34:5 (2014).
  • Norenzayan, Ara. Big Gods: How Religion Transformed Cooperation and Conflict. Princeton: Princeton, 2013.
  • Pagel, Mark. Wired for Culture: Origins of the Human Social Mind. New York: Norton, 2012.
  • Richerson, Peter, and Robert Boyd. Not by Genes Alone: How Culture Transformed Human Evolution. Chicago: Chicago, 2005.
  • Tomasello, Michael. A Natural History of Human Morality. Cambridge: Harvard, 2016.
  • Waal, Frans de. “Natural normativity: The ‘Is’ and ‘Ought’ of Animal Behavior,” Behaviour 151 No. 2–3 (2014).
  • ———. Primates and Philosophers: How Morality Evolved. Princeton: Princeton, 2006.
  • Wilson, Edward O. The Meaning of Human Existence. New York: Norton, 2014.

Doug Mann

Doug Mann, PhD, is an experimental psychologist and former medical school professor. Research on empathy in the doctor-patient relationship led to his post-retirement interest in moral psychology and the evolution of morality.

Since Charles Darwin published The Descent of Man, his second major book about evolution, in 1871, researchers have made many discoveries that flesh out Darwin’s little-known ideas about the evolution of morality. Recent papers in Free Inquiry by Ronald Lindsay and James Hughes have touched briefly on the evolution of morality, but there’s much more …

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