When Wilson published Sociobiology in 1975 and extended its argument to human beings, his critics leveled a charge that stung and that he came to regard as partly fair: that his account of human behavior neglected culture, treating the mind as a set of fixed genetic programs and leaving no room for the learning, cognition, and cultural transmission that so plainly shape human life. In the years that followed, Wilson set out to answer this charge, not by retreating from his biological convictions but by building a more sophisticated theory of exactly how genes and culture interact. The result, worked out with the physicist and theoretical biologist Charles Lumsden and published in 1981 as Genes, Mind and Culture, was the theory of gene-culture coevolution — Wilson's most technical and ambitious attempt to bridge the gap between biology and the human sciences. This chapter examines that theory: its central mechanism of epigenetic rules, its account of the coevolutionary circuit binding genes to culture, and its bold and contested claim to have found the missing link between evolutionary biology and the study of human society.
The problem the theory addressed was one Wilson had felt acutely since the sociobiology controversy: the artificial separation between evolutionary biology and the social sciences, two great bodies of knowledge that studied the same creature — the human being — yet remained almost wholly disconnected. Lumsden and Wilson opened their book by naming this missing linkage as the central problem, arguing that the social sciences floated free of their biological foundations while biology, in turn, had failed to reckon adequately with the reality of culture. Their aim was to forge the connection, to show precisely how the genes influence culture and how culture, in turn, influences the genes, and thereby to unite the two estranged disciplines in a single explanatory framework. This was consilience in action (see Chapter 13), the attempt to bridge one of the widest gaps in human knowledge — and it required, as its central technical achievement, a mechanism specific enough to carry causal influence across the divide between the biological and the cultural.
That mechanism was the concept of epigenetic rules, which lies at the heart of the whole theory. Epigenetic rules, as Lumsden and Wilson defined them, are inherited regularities of development — biases, built into the growing mind by the genes, that channel the way individuals perceive the world, process information, learn, and choose among the options their culture presents. The genes do not, on this account, prescribe specific behaviors or cultural forms directly; what they prescribe are rules of mental development that make some perceptions, some associations, some choices easier and more likely than others. The mind is not a blank slate on which culture writes freely, but neither is it a rigid program; it is a biased learner, predisposed by its inherited developmental rules to acquire certain things more readily than others and to lean, in its cultural choices, in certain directions rather than others. The epigenetic rules are the channel through which the genes exert their influence on culture — not by dictating its content, but by tilting the probabilities of what the developing human mind will take up and pass on.
Lumsden and Wilson distinguished two levels of these rules, corresponding to two stages of mental processing. The primary epigenetic rules govern the earliest and more automatic stages, the raw processing of sensory information below the level of conscious awareness — the way the eye and brain carve the continuous spectrum of light into discrete color categories, for instance, which the authors used as a paradigm case of a primary rule shaping perception in ways largely universal across humanity. The secondary epigenetic rules operate at the higher, more integrative stages of cognition, guiding how the perceptions delivered by the primary rules are evaluated, remembered, and acted upon, and biasing the choices individuals make among cultural alternatives. It was the secondary rules, Lumsden and Wilson argued, that chiefly shape cultural pattern, for they are the ones that bias the adoption of one custom over another, one belief over another, one practice over another, across the whole range of cultural life. Together the two tiers of rules describe a mind that processes the world not neutrally but according to inherited biases at every level, from the perception of a color to the choice of a mate.
The epigenetic rules were, in essence, a generalization and systematization of a set of developmental phenomena Wilson had been assembling since On Human Nature, drawn from developmental and cognitive psychology. Chief among them was prepared learning — the observation that human beings acquire some associations and fears far more readily than others, as though the mind were primed in advance to learn certain lessons. The classic example is the ease with which humans acquire fears of snakes and spiders, ancient dangers to our ancestors, compared with the difficulty of learning to fear the guns and electrical outlets that actually threaten modern life; the mind comes prepared to learn the ancestral fear, and prepared learning of this kind is precisely an epigenetic rule in action. Wilson linked this to the broader phenomenon of canalization — the tendency of development to arrive at species-typical outcomes across a wide range of environments, as though channeled toward them — and to the existence of critical periods, windows in development during which certain experiences must occur for normal growth, as in the acquisition of language. These developmental concepts gave the abstract notion of epigenetic rules a concrete grounding in the observed regularities of how human minds actually grow.
Language itself furnished Wilson one of his most compelling illustrations of biology and culture interwoven. The human capacity for language, he argued, is a biologically prepared ability: children acquire the astonishingly complex structure of their native tongue rapidly and spontaneously, on the basis of fragmentary and imperfect input, guided by an inherited readiness to learn language that no other species possesses. Yet the particular language a child learns is entirely cultural, determined by the community into which the child happens to be born. Language thus displays exactly the interweaving the theory described: a universal, biologically grounded capacity, expressed always in a specific, culturally transmitted form, the innate and the learned inseparable in the finished result. No account that assigned language wholly to nature or wholly to nurture could make sense of it; only an account in which an inherited developmental readiness meets and takes up the materials of a particular culture could capture how human beings come to speak.
The paradigm case that Lumsden and Wilson returned to again and again, the clearest illustration of an epigenetic rule shaping culture, was the human aversion to incest. Across virtually all human societies, people raised together in early childhood develop a strong sexual aversion to one another in adulthood — a phenomenon known as the Westermarck effect — and this deep, largely unlearned aversion expresses itself, at the cultural level, in the near-universal incest taboos that human societies have erected. Here, the authors argued, was a visible chain running all the way from gene to culture: an inherited developmental rule (the aversion that forms during childhood co-residence), grounded in the evolutionary logic of avoiding the genetic costs of inbreeding, giving rise to a pervasive cultural institution (the taboo). Incest avoidance became the theory's showcase, the case in which the abstract machinery of epigenetic rules could be seen operating concretely, linking a biological predisposition to a cultural universal through the developing minds of individuals.
The basic unit on the cultural side of the theory Lumsden and Wilson called the culturgen — a discrete array of artifacts, behaviors, or mental constructs that functions as the unit of culture, roughly analogous to the gene on the biological side. Individuals, they argued, adopt culturgens according to probabilities shaped by their epigenetic rules: faced with an array of cultural options, a person is more likely to take up those toward which their inherited developmental biases incline them, so that the distribution of culturgens in a society reflects, in aggregate, the epigenetic rules of its members. This gave the theory a unit it could count and model, a way of rendering the flux of culture into quantities that might be tracked as they changed. The culturgen was Lumsden and Wilson's attempt to make culture tractable to the same kind of analysis that population genetics had brought to the genes — to treat the spread of a custom or an idea through a population with something of the rigor that biologists brought to the spread of a gene.
With genes on one side, culturgens on the other, and epigenetic rules linking them, Lumsden and Wilson could assemble their central construct: the coevolutionary circuit, the complete causal loop connecting genes, mind, and culture. The circuit runs in both directions. Genes prescribe the epigenetic rules of mental development; the epigenetic rules bias the choices individuals make among culturgens, and thus shape the culture; and the resulting culture, by determining which individuals survive and reproduce in a given social environment, feeds back to alter the frequencies of the very genes that prescribe the rules. Culture is shaped by biology, and biology is in turn reshaped by culture, in a continuous coevolutionary loop running across the generations. This closing of the loop was the theoretical heart of the book, the demonstration that genes and culture are not two separate systems, one determining the other, but a single coupled system evolving together, each continually influencing the other through the mediating machinery of the developing mind.
Crucially, the epigenetic rules were themselves subject to natural selection, and this closed the loop in the deepest way. Lumsden and Wilson examined how selection acts on the rules themselves, favoring those biases of perception and learning that led, in the ancestral environment, to adaptive choices — to the selection of culturgens that enhanced survival and reproduction — and disfavoring those that led astray. The rules that incline us to fear snakes, to avoid incest, to prefer certain landscapes and faces and foods, are on this account not arbitrary but the products of a long selective history in which minds biased in these particular ways left more descendants than minds biased otherwise. The genes that build the epigenetic rules, in other words, rise and fall in frequency according to the reproductive consequences of the cultural choices those rules encourage, so that the mind's biases are continually tuned, over evolutionary time, to the business of living. This was the sense in which culture reached back to reshape biology: by making certain gene-culture combinations more successful than others, the cultural environment selected among the very genes that prescribed the mind's dispositions.
To visualize the possible outcomes of this coevolution, Lumsden and Wilson borrowed the image of an adaptive landscape, a terrain of peaks and valleys in which the peaks represent stable, adaptive configurations of genes and culturgens toward which the coevolutionary process tends to climb. Certain combinations of genetic predisposition and cultural practice are mutually reinforcing and reproductively successful, forming peaks on which populations tend to settle; others are unstable or maladaptive, valleys the process moves away from. The landscape metaphor allowed the authors to think about why human cultures, for all their variety, tend to converge on certain recurrent patterns — the near-universal institutions of kinship, taboo, and the rest — as the peaks toward which the epigenetic rules, over time, steer them. The diversity of cultures represented the many peaks available to a creature on a long genetic leash; the universals represented the deepest and most stable peaks, toward which the underlying biology reliably drew human societies wherever they arose.
A striking and controversial implication of the theory concerned the speed at which this coevolution could operate. Against the common assumption that genetic change is far too slow to interact meaningfully with the rapid pace of cultural change, Lumsden and Wilson advanced what they called the thousand-year rule — the claim that gene-culture coevolution could proceed relatively rapidly, producing significant genetic change over as few as a thousand years, a span vastly shorter than usually imagined for evolutionary change. If correct, this meant that genes and culture could indeed keep pace with each other closely enough to coevolve as a coupled system, the genetic and the cultural intertwining on timescales that overlapped. The claim was among the most debated in the book, for it hinged on technical assumptions about the strength of selection on epigenetic rules that many found questionable. But it was essential to the theory's ambition, for only if genetic change could be reasonably swift could the coevolutionary loop turn fast enough to bind genes and culture into the tight, mutually shaping relationship the theory proposed.
What set Genes, Mind and Culture apart from Wilson's earlier work, and what made it so demanding a book, was its commitment to rendering these ideas in explicit mathematics. Lumsden and Wilson did not rest content with the verbal argument that genes and culture coevolve; they built quantitative models, deploying the machinery of population genetics and mathematical theory to predict how the frequencies of genes and culturgens would change together under the pressures of selection and cultural transmission. They confronted directly what they called the translation problem — the technical challenge of moving rigorously from the epigenetic rules operating in the mind of an individual to the patterns of culture observable at the level of a whole society, from micro to macro. And they went so far as to derive predicted distributions of cultural traits across societies, patterns that might in principle be checked against the actual ethnographic record. This drive to make the theory genuinely predictive and testable, to subject the relationship between biology and culture to quantitative discipline, was its boldest methodological aspiration — and also, for many readers, its most vulnerable point, for the models rested on assumptions and simplifications that were difficult to verify.
Underlying the whole theory was a resolution of the ancient nature-nurture debate that Wilson had been developing since On Human Nature, and that gene-culture coevolution now expressed in its most refined form. The old opposition between nature and nurture, between heredity and environment, was for Wilson a false one, resting on a misunderstanding of how development works. Genes do not determine behavior directly, bypassing experience; rather, genetic predispositions express themselves only through development in an environment, so that every trait is the product of nature acting through nurture, heredity and experience woven together at every step. The epigenetic rules are precisely the form this interweaving takes — inherited biases that do not fix behavior but shape the way experience is processed and learned from. Wilson thus rejected both the genetic determinism his critics accused him of and the pure environmentalism he attributed to his opponents, staking out a middle position in which biology and culture are not competing explanations but partners in a single developmental process. Human nature, on this view, is neither written wholly in the genes nor imposed wholly by culture, but arises from the continuous interaction of the two.
Wilson buttressed this position with empirical evidence against the pure environmentalism that had dominated mid-century social science — the view that human behavior is almost infinitely malleable, shaped entirely by culture and learning, the mind a blank slate at birth. Against this view he marshaled two main lines of evidence. The first was the existence of human universals: behaviors and institutions that recur across virtually all human societies, however different their histories and environments — the incest taboos, the kinship classifications, the division of labor, the status-seeking, the facial expressions of emotion — patterns whose very universality suggested a common biological grounding rather than independent cultural invention. The second was the evidence from studies of twins and of adoption, which indicated that heredity influences not only physical traits but personality and behavioral tendencies, since individuals who share more genes tend to resemble one another in disposition even when raised apart. Neither line of evidence implied genetic determinism; both simply demonstrated that biology contributes to human behavior, that the blank-slate view was untenable, and that any adequate social science must reckon with the hereditary component of human nature. The recurrence of the same institutions across unconnected cultures, and the persistence of temperament across different upbringings, were for Wilson the visible fingerprints of the epigenetic rules at work.
The image Wilson used most memorably to capture the relationship was that of the genetic leash. Human culture, he argued, however elaborate and varied it becomes, is held on a leash by the genes — free to range widely, to take countless different forms across societies and eras, but ultimately constrained and biased by the underlying epigenetic rules, which pull culture, over time, back toward configurations compatible with human biological nature. The leash is long, allowing culture great latitude; but it is real, and it prevents culture from wandering into forms that run permanently against the grain of the evolved human mind. This was Wilson's answer to those who held culture to be infinitely malleable, capable of shaping human beings into any form whatever: culture is powerful, he conceded, but not omnipotent, for it works always upon a human nature that is not infinitely plastic but structured by its evolutionary inheritance. The genetic leash expressed both the freedom and the constraint of the human condition — the vast but not unlimited range of cultural possibility open to a biologically shaped creature.
Wilson was careful, especially in the face of his critics, to specify the limits of what this genetic influence meant, and to reject the charge of genetic determinism. Genes prescribe tendencies and capacities, he insisted, not fixed and inevitable behaviors; they bias the odds without dictating the outcome, incline without compelling. The epigenetic rules make certain things easier to learn, certain choices more likely, certain fears and preferences more readily acquired — but they leave enormous room for variation, for individual difference, for the shaping power of particular circumstances and cultures. To say that human nature has a genetic basis was not, Wilson maintained, to say that human behavior is genetically fixed or that individuals are prisoners of their biology; it was to say that the human mind comes equipped with inherited biases that shape, without determining, the vast cultural edifice it builds. This careful qualification was central to Wilson's self-defense against the political charges that had dogged sociobiology (see Chapter 6), his insistence that a biology of human nature need not underwrite any fatalism about the human future.
Gene-culture coevolution was, in Wilson's own estimation, the natural next step beyond classical sociobiology — the answer to the charge that his earlier work had slighted the mind and culture, and the fulfillment of sociobiology's promise to connect biology to the full range of human phenomena. He and Lumsden presented it explicitly as the next synthesis, the successor to the modern synthesis of evolutionary biology and to the sociobiological synthesis that had extended Darwinism to social behavior, now extended further to encompass the human mind and human culture within a single evolutionary framework. Where classical sociobiology had sometimes seemed to leap directly from genes to behavior, gene-culture coevolution inserted the crucial mediating machinery of the developing, learning, choosing mind, and thereby addressed the very gap its critics had identified. It was Wilson's most serious attempt to make good on the deepest ambition of his human science: to show that culture, far from standing outside biology, is bound to it through the epigenetic rules of the mind, and that the two evolve together as a single, coupled system.
The reception of the theory was, it must be said, decidedly mixed, and Genes, Mind and Culture did not achieve the influence Wilson hoped for. Its heavy mathematical apparatus made it difficult and forbidding to the social scientists it most needed to persuade, while the very assumptions on which its models rested — the definition of the culturgen, the strength of selection on epigenetic rules, the thousand-year rule — struck many specialists as speculative or unverifiable. The book was more admired for its ambition than adopted for its methods, and the specific technical program of Lumsden and Wilson did not become the bridge between biology and the social sciences that they had envisioned. Yet the core idea — that human culture is shaped by inherited biases of mind, that gene and culture coevolve, that the study of human behavior must reckon with the biology of the mind that produces it — proved durable and influential, feeding into the later development of evolutionary psychology and the broader project of grounding the human sciences in biology. If the elaborate machinery of the theory did not endure, its central insight did.
Seen in the sweep of Wilson's career, gene-culture coevolution occupies a crucial place: it was the hinge on which his human science turned from the controversies of sociobiology toward the mature synthesis of his later years. Having been accused of biological determinism, Wilson answered by developing the most sophisticated available account of how biology and culture interact — an account that gave culture its full due while insisting on its biological foundations, that granted the human mind its powers of learning and choice while tracing the inherited biases that shape them. The theory of epigenetic rules and the coevolutionary circuit was his considered response to the deepest question his work had raised: not whether human behavior is shaped by biology or by culture, but how the two are woven together in the development of every human being. That the technical details did not all survive matters less than the vision they served — the vision of a human nature genuinely continuous with the rest of life, bound to its evolutionary past by the epigenetic rules of the mind, yet free within that inheritance to build the vast and varied cultures that are humanity's distinction. The chapters on human nature that follow take up the fruits of this synthesis (see Chapter 16, Human Evolution & Sociobiology, and Chapter 18, The Psychology of Human Nature).