In his recent speech to Congress, Anatoly Shcharansky said, “All understanding between the East and West must be based on human values common to all men.” This appealing statement takes us straight to the central question of moral reasoning: What, if anything, are common human values?

Humanity is and always has been faced with a choice among three metaethics, three differing views of how the world works from the top down and hence, the ultimate means for the selection of moral codes. If behavior is based exclusively on cultural evolution, the codes can drift apart until societies face each other like alien species. If on the other hand morality must be read from the graven tablets of particular religions, we are equally likely to come to an impasse. Dogmas arise in special historical circumstances, are commonly inadequate for contemporary dilemmas, and tend to enhance rather than reduce the alienation of cultures—the process Erik Erikson called pseudo-speciation. Finally, if morality represents the upwelling of deep impulses that were somehow encoded in our genes during evolution, our ignorance of such matters remains general and dangerous.

I may be wrong, but I believe that the correct metaethic is the third, fundamentally materialistic one. It works in the following way. Our profound impulses are rooted in a genetic heritage common to the entire species. These propensities are transmuted through culture into specific moral codes, which are integrated into religion and the sacralized memories of revolutions, conquests, and other historical events by which cultures secured their survival. Although variations in the final codes are inevitable, different societies share a great deal in their perception of right and wrong. By making the search for these similarities part of the scientific enterprise, and taking religious behavior very seriously as a key part of human nature, a tighter consensus of ethical behavior might be reached.

Modern biology appears to have banished nihilism. But in so doing it has not led to a narrow form of genetic determinism. It is not true that certain genes prescribe particular responses or that moral codes must be the exact equivalent of our biological nature. I have never met a genetic determinist by this definition. Most or all biologists who study behavior, especially social behavior, are interactionists—they view final thought and response as the product of a complex interplay of genes and environment. Social behavior in human beings is the result of biologically based predispositions filtered and hammered into final shape by the particular cultures in which individuals are reared. On the other hand, I have met many cultural determinists, especially among the reigning social theorists. They deny or at least wholly ignore the influence of biology. The evidence—fortunately or unfortunately depending on how you view it—has proved them wrong. I would say fortunately, because any species wholly dominated by culture and free of genetic constraint would run a grave risk of moral nihilism.

A case in point, out of many now known in human cognitive development, is the avoidance of brother-sister incest. In order to avoid misunderstanding, let me define incest as strong sexual bonding among close biological relatives that includes intercourse, of the kind generally associated with cohabitation and procreation, and excludes transient forms of adolescent experimentation. Incest taboos are very nearly universal as a cultural norm. About a dozen societies during historical times—ancient Egyptians, Bunyoro, Nyanza, and so on—institutionalized brother-sister incest for royalty and a few other groups of high status. But the practice is (or was) hedged with ritual, and in every instance the incestuous males are (or were) permitted to take additional wives and hence to practice outbreeding.

The avoidance of brother-sister incest originates in what psychologists have called prepared learning. This means that people are innately prone to learn one alternative as opposed to another. They pick it up more readily, they enjoy it more, or both. The avoidance of sibling-incest comes from the “potty rule” in mental development: individuals reared in close domestic proximity during the first six years of life (they share the same potty) are automatically inhibited from strong sexual attraction and bonding when they reach sexual maturity. The rule works even when the children reared together are biologically unrelated and later encouraged to marry and have children, as in the Israel kibbutzim and traditional minor marriages (simpua) of prerevolutionary China. Those affected are usually quite unable to offer a rational explanation of why they feel no attraction. Some unconscious process ticked over in the brain, and the urge, they explain, never came.

The inhibitory rule is an example not only of prepared learning but also of “proximate causation” as it is conceptualized by evolutionary biologists. This means that it channels a response of importance to the survival or reproduction of the organism. Proximate causes are put into place by the assembly of. genes through the process of natural selection. The ultimate causation, in other words the particular selection regime that enabled certain genes to predominate in the first place, is the well-documented effect of inbreeding depression. When mating occurs between brother and sister, father and daughter, or mother and son, the probability of matching debilitating genes in both homologous chromosomes of the offspring is greatly increased. The end result is a rise in abortion, birth defects, and genetic disease. Hence genes prescribing a biological propensity’ to avoid incest will be favored over those that do not. Most animal and plant species display proximate devices of one kind or another, and it does indeed protect them from inbreeding depression. In some, the response is rigidly determined. In others, especially the brighter mammals, it is based on prepared learning. Interestingly enough, the human proximate form is nearly identical to that of the chimpanzee.

It is exquisitely human to semanticize innate tendencies. In many societies incest avoidance is underwritten by Symbolically transmitted taboos, myths, and laws. These, not the emotions and programs of prepared learning, are the values we perceive by casual observation. They are easily transmitted from one person to the next, and the most readily studied by scholars. But the phenomenon of greatest interest is their etiology: the chain of events leading from ultimate cause in natural selection to proximate cause in prepared learning to reification and legitimation in culture. If the terminal cultural form were somehow to be stripped away by a collective loss of memory, people would still avoid sibling incest. Given enough time, they would most likely invent religious and ethical rationalizations to justify their feelings.

Crude genetic determinism has no part in this process. The existence of the three-step etiology in mental development in no way constricts free will. Individual choice persists even when learning is strongly prepared by heredity. If some future society decides to encourage brother-sister incest, for whatever bizarre reason, it now has the knowledge to do so efficiently. The possibility, however, is vanishingly remote, because the same knowledge tells us that incest avoidance is programmed as a powerful rule and protects families from genetic damage. We are likely to agree still more firmly that the avoidance is a part of human nature to be fostered. In other words, incest avoidance is and will continue to be one of our common values.

This approach to moral reasoning is consistent with the relatively new discipline of sociobiology, but it is not an essential part—or even necessarily correct! Sociobiology strictly defined is the systematic study of the biological basis of social behavior. It is part of the mainstream of the biological sciences. But as its practitioners have extended their modes of analysis into the domain for human behavior, they have run into trouble precisely because of the sometimes unwelcome implications for social theory. In my opinion, shared by some but far from all other scientists, this is the way to go; the materialistic metaethic is essentially correct. However, applications to specific moral problems are always subject to additional evidence and new challenges.

They are also subject to questions about the generality of their importance. It will immediately occur to the reader that incest avoidance might rank as nothing more than a special case. There is a vast difference between this relatively simple phenomenon and economic cycles, religious rites, and Presidential elections. Might such particularities fall within a wholly different domain of explanation and require a different metaethic? Perhaps, but I don’t think so.

The evidence favoring the evolutionary approach to moral reasoning is as follows. By mid-1985 no fewer than 3,577 human genes had been identified, of which about 600 had been placed on one or another of the 23 pairs of chromosomes. This is a respectable fraction of the entire human complement, since Homo sapiens is a Class III species with no more than several hundred thousand genes (it is what the genes do, not their absolute number, that counts). New techniques for separation and identification make it possible eventually to map all of the genes, perhaps by early in the next century. Hundreds of the genes already known alter behavior in one way or another. In most cases the effect is crude or indirect. But a few change behavior in a precise manner, as for example those modulating depression, reading ability, and performance on spatial tests. Twin and adoption studies have implicated other genes, as yet unmapped and probably working in complex multiples, in schizophrenia, propensity toward homosexuality, performance on tests measuring empathy, and a wide range of personality traits from introversion-extroversion to athleticism and proneness to alcoholism. Moreover, prepared learning and biases in perception have been discovered in virtually every category of behavior thus far studied.

Of equal importance, people often behave as though they were acting in their genetic self-interest, even when this end result is not easily deduced during everyday life. For example, men tend to favor the children of their sisters (whose genetic relatedness is easily proven) over the children of their brothers. The avuncular bias is strongest in those societies when paternity is generally least certain. Such correlations do not always exist. Recent studies have found that in contemporary industrial societies reproduction often decreases with wealth and status rather than the opposite as predicted by natural selection theory. But the trends do occur frequently enough to invite serious attention. In their seminal book The Biology of Religion, Vernon Reynolds and Ralph Tanner showed that survival and genetic reproduction can be favored by the traditional practices of religion, including evangelism, marriage rites, and even celibacy and asceticism, the latter through their positive effects on group cohesion and welfare.

But to come quickly to the point that most troubles critics of evolutionary ethics, it does not follow that the genetic programs of cognition and prepared learning are automatically beneficial even in a crude Darwinian sense. Behaviors such as xenophobia and territorial expansion may have been very adaptive in the earlier, formative stages of human evolutionary history, but they are destructive now even for those who practice them. Although the cultural ought is more tightly linked to the genetic is than philosophers have traditionally conceded, the two do not automatically translate one into the other.

A workable moral code can be obtained not just by understanding the foundations of human nature, but by the wise choice of those constraints needed to keep us alive and free in a rapidly changing cultural environment that renders some of our propensities maladaptive.

The choice among the foundations of moral reasoning is not likely to remain arbitrary. Metaethics can be tested empirically. Already, it seems necessary on the basis of the evidence to discard cultural relativism. One system of ethics is not as good as another. Not only are some less workable, they are in the profoundest sense less human. The corollary is that people can be educated readily only to a narrow range of ethical precepts. This leaves a choice between evolutionary ethics and transcendentalism. The idea of a genetic origin of moral codes can be further tested by a continuance of biological studies of complex human behavior, including religious behavior itself. To the extent that the sensory and nervous systems appear to have evolved by natural selection or some other purely natural process, the evolutionary interpretation will be supported. To the extent they are not, the evolutionary interpretation will have to be abandoned and a transcendental explanation sought.

Human curiosity is a juggernaut that will eventually strain our very notion of the meaning of science and religion. Somewhere out there we might even find a surprising conjunction of traditional religion and secular humanism. I doubt that what lies ahead will be specially congenial to any existing ideology or religious belief Yet to press on is infinitely superior than to retreat through fear and distaste. Enrico Fermi put it as follows: “Whatever Nature has in store for mankind, unpleasant as it may be, man must accept, for ignorance is ever better than knowledge.”

To the distinguished inventor of the nuclear reactor we may now respond in the face of more advanced biological knowledge: yes, but let us step very carefully.