From the issue dated September 22, 2000
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The Tangled Skeins of Nature and Nurture in Human EvolutionBy PAUL R. EHRLICHWhen we think about our behavior as individuals, "Why?" is a question almost always on the tips of our tongues. Sometimes that question is about perceived similarities: why is almost everyone religious; why do we all seem to crave love; why do most of us like to eat meat? But our differences often seem equally or more fascinating: why did Sally get married although her sister Sue did not, why did they win and we lose, why is their nation poor and ours rich? What were the fates of our childhood friends? What kinds of careers did they have; did they marry; how many children did they have? Our everyday lives are filled with why's about differences and similarities in behavior, often unspoken, but always there. Why did one of my closest colleagues drink himself to death, whereas I, who love wine much more than he did, am managing to keep my liver in pretty good shape? Why, of two very bright applicants admitted to our department at Stanford University for graduate work, does one turn out pedestrian science and another have a spectacular career doing innovative research? Why are our natures often so different, and why are they so frequently the same? The background needed to begin to answer all these whys lies within the domain of human biological and cultural evolution, in the gradual alterations in genetic and cultural information possessed by humanity. It's easy to think that evolution is just a process that sometime in the distant past produced the physical characteristics of our species but is now pretty much a matter of purely academic, and local school board, interest. Yet evolution is a powerful, ongoing force that not only has shaped the attributes and behaviors shared by all human beings but also has given every single individual a different nature. A study of evolution does much more than show how we are connected to our roots or explain why people rule Earth -- it explains why it would be wise to limit our intake of beef Wellington, stop judging people by their skin color, concern ourselves about global warming, and reconsider giving our children antibiotics at the first sign of a sore throat. Evolution also provides a framework for answering some of the most interesting questions about ourselves and our behavior. When someone mentions evolution and behavior in the same breath, most people think immediately of the power of genes, parts of spiral-shaped molecules of a chemical called DNA. Small wonder, considering the marvelous advances in molecular genetics in recent decades. New subdisciplines such as evolutionary medicine and evolutionary psychology have arisen as scientists have come to recognize the importance of evolution in explaining contemporary human beings, the network of life that supports us, and our possible fates. And the mass media have been loaded with stories about real or imagined links between every conceivable sort of behavior and our genes. Biological evolution -- evolution that causes changes in our genetic endowment -- has unquestionably helped shape human natures, including human behaviors, in many ways. But numerous commentators expect our genetic endowment to accomplish feats of which it is incapable. People don't have enough genes to program all the behaviors some evolutionary psychologists, for example, believe that genes control. Human beings have something on the order of 100,000 genes, and human brains have more than one trillion nerve cells, with about 100-1,000 trillion connections (synapses) between them. That's at least one billion synapses per gene, even if each and every gene did nothing but control the production of synapses (and it doesn't). Given that ratio, it would be quite a trick for genes typically to control more than the most general aspects of human behavior. Statements such as "Understanding the genetic roots of personality will help you 'find yourself' and relate better to others" are, at today's level of knowledge, frankly nonsensical. The notion that we are slaves to our genes is often combined with reliance on the idea that all problems can be solved by dissecting them into ever smaller components -- the sort of reductionist approach that has been successful in much of science but is sometimes totally unscientific. It's like the idea that knowing the color of every microscopic dot that makes up a picture of your mother can explain why you love her. Scientific problems have to be approached at the appropriate level of organization if there is to be a hope of solving them. That combination of assumptions -- that genes are destiny at a micro level and that reductionism leads to full understanding -- is now yielding distorted views of human behavior. People think that coded into our DNA are "instructions" that control the details of individual and group behavior: that genetics dominates, heredity makes us what we are, and what we are is changeable only over many generations as the genetic endowment of human populations evolves. Such assertions presume, as I've just suggested, that evolution has produced a level of genetic control of human behavior that is against virtually all available evidence. For instance, ground squirrels have evolved a form of "altruistic" behavior -- they often give an alarm call to warn a relative of approaching danger. Evidence does indicate that this behavior is rooted in their genes; indeed, it probably evolved because relatives have more identical genes than do unrelated individuals. But some would trace the "altruistic" behavior of a business executive sending a check to an agency helping famine victims in Africa, or of a devout German Lutheran aiding Jews during the Holocaust, to a genetic tendency as well. In this view, we act either to help relatives or in the expectation of reciprocity -- in either case promoting the replication of "our" genes. But experimental evidence indicates that not all human altruistic behavior is self-seeking -- that human beings, unlike squirrels, are not hereditarily programmed only to be selfish. Another false assumption of hereditary programming lies behind the belief that evolution has resulted in human groups of different quality. Many people still claim (or secretly believe), for example, that blacks are less intelligent than whites and women less "logical" than men, even though those claims are groundless. Belief in genetic determinism has even led some observers to suggest a return to the bad old days of eugenics, of manipulating evolution to produce ostensibly more skilled people. Advocating programs for the biological "improvement of humanity" -- which in the past has meant encouraging the breeding of supposedly naturally superior individuals -- takes us back at least to the days of Plato, more than two millennia ago, and it involves a grasp of genetics little more sophisticated than his. Uniquely in our species, changes in culture have been fully as important in producing our natures as have changes in the hereditary information passed on by our ancestors. Culture is the nongenetic information (socially transmitted behaviors, beliefs, institutions, arts, and so on) shared and exchanged among us. Indeed, our evolution since the invention of agriculture, about 10,000 years ago, has been overwhelmingly cultural because, as we shall see, cultural evolution can be much more rapid than genetic evolution. There is an unhappy predilection, especially in the United States, not only to overrate the effect of genetic evolution on our current behavior but also to underrate that of cultural evolution. The power of culture to shape human activities can be seen immediately in the diversity of languages around the world. Although, clearly, the ability to speak languages is a result of a great deal of genetic evolution, the specific languages we speak are just as clearly products of cultural evolution. Furthermore, genetic evolution and cultural evolution are not independent. There are important "coevolutionary" interactions between them. To take just one example, our farming practices (an aspect of our culture) change our physical environment in ways that alter the evolution of our blood cells. Not only is the evolution of our collective nongenetic information critical to creating our natures, but also the rate of that evolution varies greatly among different aspects of human culture. That, in turn, has profound consequences for our behavior and our environments. A major contemporary human problem, for instance, is that the rate of cultural evolution in science and technology has been extraordinarily high in contrast with the snail's pace of change in the social attitudes and political institutions that might channel the uses of technology in more beneficial directions. No one knows exactly what sorts of societal effort might be required to substantially redress that imbalance in evolutionary rates, but it is clear to me that such an effort, if successful, could greatly brighten the human prospect. Science has already given us pretty good clues about the reasons for the evolution of some aspects of our natures; many other aspects remain mysterious despite a small army of very bright people seeking reasons. Still others (such as why I ordered duck in the restaurant last night rather than lamb) may remain unanswerable -- for human beings have a form of free will. But even to think reasonably about our natures and our prospects, some background in basic evolutionary theory is essential. If Grace is smarter than Pedro because of her genes, why did evolution provide her with "better" genes? If Pedro is actually smarter than Grace but has been incorrectly evaluated by an intelligence test designed for people of another culture, how did those cultural differences evolve? If I was able to choose the duck for dinner because I have free will, what exactly does that mean? How did I and other human beings evolve that capacity to make choices without being complete captives of our histories? Could I have exercised my free will to eat a cockroach curry had we been in a restaurant that served it (as some in Southeast Asia do)? Almost certainly not -- the very idea nauseates me, probably because of an interaction between biological and cultural evolution. Every attribute of every organism is, of course, the product of an interaction between its genetic code and its environment. Yes, the number of heads an individual human being possesses is specified in the genes and is the same in a vast diversity of environments. And the language or languages a child speaks (but not her capacity to acquire language) is determined by her environment. But without the appropriate internal environment in the mother's body for fetal development, there would be no head (or infant) at all; and without genetically programmed physical structures in the larynx and in the developing brain, there would be no capacity to acquire and speak language. Beyond enabling us to make such statements in certain cases, however, the relative contributions of heredity and environment to various human attributes are difficult to specify. They clearly vary from attribute to attribute. So although it is informative to state that human nature is the product of genes interacting with environments (both internal and external), we usually can say little with precision about the processes that lead to interesting behaviors in adult human beings. We can't partition the responsibility for aggression, altruism, or charisma between DNA and upbringing. In many such cases, trying to separate the contributions of nature and nurture to an attribute is rather like trying to separate the contributions of length and width to the area of a rectangle, which at first glance also seems easy. When you think about it carefully, though, it proves impossible. Diverse notions of inherited superiority or inferiority and of characteristic innate group behaviors have long pervaded human societies: beliefs about the divine right of kings; "natural" attributes that made some people good material for slaves or slave masters; innate superiority of light-skinned people over dark-skinned people; genetic tendencies of Jews to be moneylenders, of Christians to be sexually inhibited, and of Asians to be more hardworking than Hispanics; and so on. Consider the following quote from a recent book titled Living With Our Genes, which indicates the tone even among many scientists: "The emerging science of molecular biology has made startling discoveries that show beyond a doubt that genes are the single most important factor that distinguishes one person from another. We come in large part ready-made from the factory. We accept that we look like our parents and other blood relatives; we have a harder time with the idea we act like them." In fact, the failure of many people to recognize the fundamental error in such statements (and those in other articles and books based on genetic determinism, such as Richard J. Herrnstein and Charles Murray's famous The Bell Curve) is itself an environmental phenomenon -- a product of the cultural milieu in which many of us have grown up. Genes do not shout commands to us about our behavior. At the very most, they whisper suggestions, and the nature of those whispers is shaped by our internal environments (those within and between our cells) during early development and later, and usually also by the external environments in which we mature and find ourselves as adults. How do scientists know that we are not simply genetically programmed automata? First, biological evolution has produced what is arguably the most astonishingly adaptable device that has ever existed -- the human nervous system. It's a system that can use one organ, the brain, to plan a marriage or a murder, command muscles to control the flight of a thrown rock or a space shuttle, detect the difference between a 1945 Mouton and a 1961 Latour, learn Swahili or Spanish, and interpret a pattern of colored light on a flat television screen as a three-dimensional world containing real people. It tries to do whatever task the environment seems to demand, and it usually succeeds -- and because many of those demands are novel, there is no way that the brain could be preprogrammed to deal with them, even if there were genes enough to do the programming. It would be incomprehensible for evolution to program such a system with a vast number of inherited rules that would reduce its flexibility, constraining it so that it could not deal with novel environments. It would seem equally inexplicable if evolution made some subgroups of humanity less able than others to react appropriately to changing circumstances. Men and people with white skin have just as much need of being smart and flexible as do women and people with brown skin, and there is every reason to believe that evolution has made white-skinned males fully as capable as brown-skinned women. A second type of evidence that we're not controlled by innate programs is that normal infants taken from one society and reared in another inevitably acquire the behaviors (including language) and competences of the society in which they are reared. If different behaviors in different societies were largely genetically programmed, that could not happen. That culture dominates in creating intergroup differences is also indicated by the distribution of genetic differences among human beings. The vast majority (an estimated 85 percent) is not between "races" or ethnic groups but between individuals within groups. Human natures, again, are products of similar (but not identical) inherited endowments interacting with different physical and cultural environments. Thus, the genetic "make-brain" program that interacts with the internal and external environments of a developing person doesn't produce a brain that can call forth only one type of, say, mating behavior -- it produces a brain that can engage in any of a bewildering variety of behaviors, depending on circumstances. We see the same principle elsewhere in our development; for instance, human legs are not genetically programmed to move only at a certain speed. The inherited "make-legs" program normally produces legs that, fortunately, can operate at a wide range of speeds, depending on circumstances. Variation among individuals in the genes they received from their parents produces some differences in that range (in any normal terrestrial environment, I never could have been a four-minute miler -- on the moon, maybe). Environmental variation produces some differences, too (walking a lot every day and years of acclimatization enable me to climb relatively high mountains that are beyond the range of some younger people who are less acclimatized). But no amount of training will permit any human being to leap tall buildings in a single bound, or even in two. Similarly, inherited differences among individuals can influence the range of mental abilities we possess. Struggle as I might, my math skills will never approach those of many professional mathematicians, and I suspect that part of my incapacity can be traced to my genes. But environmental variation can shape those abilities as well. I'm also lousy at learning languages (that may be related to my math incompetence). Yet when I found myself in a professional environment in which it would have been helpful to converse in Spanish, persistent study allowed me to speak and comprehend a fair amount of the language. But there are no genetic instructions or environmental circumstances that will allow the development of a human brain that can do a million mathematical calculations in a second. That is a talent reserved for computers, which were, of course, designed by human minds. Are there any behavioral instructions we can be sure are engraved in human DNA? If there are, at least one should be the urge to have as many children as possible. We should have a powerful hereditary tendency to maximize our genetic contributions to future generations, for that's the tendency that makes evolution work. Yet almost no human beings strictly obey this genetic "imperative"; environmental factors, especially cultural factors, have largely overridden it. Most people choose to make smaller genetic contributions to the future -- that is, have fewer children -- than they could, thus figuratively thwarting the supposed maximum reproduction "ambitions" of their genes. If genes run us as machines for reproducing themselves, how come they let us practice contraception? We are the only animals that deliberately and with planning enjoy sex while avoiding reproduction. We can and do "outwit" our genes -- which are, of course, witless. In this respect, our hereditary endowment made a big mistake by "choosing" to encourage human reproduction not through a desire for lots of children but through a desire for lots of sexual pleasure. There are environments (sociocultural environments in this case) in which near-maximal human reproduction has apparently occurred. For example, the Hutterites, members of a Mennonite sect living on the plains of western North America, are famous for their high rate of population growth. Around 1950, Hutterite women over the age of 45 had borne an average of 10 children, and Hutterite population growth rates exceeded 4 percent per year. Interestingly, however, when social conditions changed, the growth rate dropped from an estimated 4.12 percent per year to 2.91 percent. Cultural evolution won out against those selfish little genes. Against this background of how human beings can overwhelm genetic evolution with cultural evolution, it becomes evident that great care must be taken in extrapolating the behavior of other animals to that of human beings. One cannot assume, for example, that because marauding chimpanzees of one group sometimes kill members of another group, selection has programmed warfare into the genes of human beings (or, for that matter, of chimps). And although both chimp and human genetic endowments clearly can interact with certain environments to produce individuals capable of mayhem, they just as clearly can interact with other environments to produce individuals who are not aggressive. Observing the behavior of nonhuman mammals -- their mating habits, modes of communication, intergroup conflicts, and so on -- can reveal patterns we display in common with them, but those patterns certainly will not tell us which complex behaviors are "programmed" inalterably into our genes. Genetic instructions are of great importance to our natures, but they are not destiny. There are obviously limits to how much the environment ordinarily can affect individual characteristics. No known environment, for example, could have allowed me to mature with normal color vision: like about 8 percent of males, I'm color-blind -- the result of a gene inherited from my mother. But the influence on many human attributes of even small environmental differences should not be underestimated. Consider the classic story of the "Siamese twins" Chang and Eng. Born in Siam (now Thailand) on May 11, 1811, these identical twins were joined at the base of their chests by an arm-like tube that in adulthood was five or six inches long and about eight inches in circumference. They eventually ended up in the United States, became prosperous as sideshow attractions, and married sisters. Chang and Eng farmed for a time, owned slaves before the Civil War, and produced both many children and vast speculation about the circumstances of their copulations. They were examined many times by surgeons who, working before the age of X-rays, concluded that it would be dangerous to try to separate them. From our perspective, the most interesting thing about the twins is their different natures. Chang was slightly shorter than Eng, but he dominated his brother and was quick-tempered. Eng, in contrast, was agreeable and usually submissive. Although the two were very similar in many respects, in childhood their differences once flared into a fistfight, and as adults on one occasion they disagreed enough politically to vote for opposing candidates. More seriously, Chang drank to excess and Eng did not. Partly as a result of Chang's drinking, they developed considerable ill will that made it difficult for them to live together -- they were constantly quarreling. In old age, Chang became hard of hearing in both ears, but Eng became deaf only in the ear closer to Chang. In the summer of 1870, Chang suffered a stroke, which left Eng unaffected directly but bound him physically to an invalid. On January 17, 1874, Chang died in the night. When Eng discovered his twin's death, he (although perfectly healthy) became terrified, lapsed into a stupor, and died two hours later, before a scheduled surgical attempt was to have been made to separate the two. An autopsy showed that the surgeons had been correct -- the twins probably would not have survived an attempt to separate them. Chang and Eng demonstrated conclusively that genetic identity does not necessarily produce identical natures, even when combined with substantially identical environments -- in this case only inches apart, with no sign that their mother or others treated them differently as they grew up. Quite subtle environmental differences, perhaps initiated by different positions in the womb, can sometimes produce substantially different behavioral outcomes in twins. In this case, in which the dominant feature of each twin's environment clearly was the other twin, the slightest original difference could have led to an escalating reinforcement of differences. The nature-nurture dichotomy, which has dominated discussions of behavior for decades, is largely a false one -- all characteristics of all organisms are truly a result of the simultaneous influences of both. Genes do not dictate destiny in most cases (exceptions include those serious genetic defects that at present cannot be remedied), but they often define a range of possibilities in a given environment. The genetic endowment of a chimpanzee, even if raised as the child of a Harvard professor, would prevent it from learning to discuss philosophy or solve differential equations. Similarly, environments define a range of developmental possibilities for a given set of genes. There is no genetic endowment that a child could get from Mom and Pop that would permit the youngster to grow into an Einstein (or a Mozart or a García Marquez -- or even a Hitler) as a member of an isolated rain-forest tribe without a written language. Attempts to dichotomize nature and nurture almost always end in failure. Although I've written about how the expression of genes depends on the environment in which the genes are expressed, another way of looking at the development of a person's nature would have been to examine the contributions of three factors: genes, environment, and gene-environment interactions. It is very difficult to tease out these contributions, however. Even under experimental conditions, where it is possible to say something mathematically about the comparative contributions of heredity and environment, it can't be done completely because there is an "interaction term." That term cannot be decomposed into nature or nurture because the effect of each depends on the contribution of the other. To construct an artificial example, suppose there were a gene combination that controlled the level of a hormone that tended to make boys aggressive. Further, suppose that watching television also tended to make boys aggressive. Changing an individual's complement of genes so that the hormone level was doubled and also doubling the television-watching time might, then, quadruple some measure of aggressiveness. Or, instead, the two factors might interact synergistically and cause the aggression level to increase fivefold (perhaps television is an especially potent factor when the viewer has a high hormone level). Or the interaction might go the other way -- television time might increase aggression only in those with a relatively low hormone level, and doubling both the hormone level and the television time might result in only a doubling of aggression. Or perhaps changing the average content of television programming might actually reduce the level of aggressiveness so that even with hormone level and television time doubled, aggressiveness would decline. Finally, suppose that, in addition, these relationships depended in part on whether or not a boy had attentive and loving parents who provided alternative interpretations of what was seen on television. In such situations, there is no way to make a precise statement about the contributions of "the environment" (television, in this case) to aggressiveness. This example reflects the complexity of relationships that has been demonstrated in detailed studies of the ways in which hormones such as testosterone interact with environmental factors to produce aggressive behavior. The best one can ordinarily do in measuring what genes contribute to attributes (such as aggressiveness, height, or I.Q. test score) is calculate a statistical measure known as heritability. That statistic tells how much, on average, offspring resemble their parents in a particular attribute in a particular set of environments. Heritability, however, is a measure that is difficult to make and difficult to interpret. That is especially true in determining heritability of human traits, where it would be unethical or impossible to create the conditions required to estimate it, such as random mating within a population. Despite these difficulties, geneticists are gradually sorting out some of the ways genes and environments can interact in experimental environments and how different parts of the hereditary endowment interact in making their contribution to the development of the individual. One of the key things they are learning is that it is often very difficult for genetic evolution to change just one characteristic. That's worth thinking about the next time someone tells you that human beings have been programmed by natural selection to be violent, greedy, altruistic, or promiscuous, to prefer certain facial features, or to show male (or white) dominance. At best, such programming is difficult; often it is impossible. Today's debates about human nature -- about such things as the origins of ethics; the meanings of consciousness, self, and reality; whether we're driven by emotion or reason; the relationship between thought and language; whether men are naturally aggressive and women peaceful; and the role of sex in society -- trace far back in Western thought. They have engaged thinkers from the pre-Socratic philosophers, Plato, and Aristotle to René Descartes, John Locke, Georg Wilhelm Friedrich Hegel, Charles Sanders Peirce, and Ludwig Wittgenstein, just to mention a tiny handful of those in the Western tradition alone. What exactly is this human nature we hear so much about? The prevailing notion is that it is a single, fixed, inherited attribute -- a common property of all members of our species. That notion is implicit in the universal use of the term in singular form. And I think that singular usage leads us astray. To give a rough analogy, human nature is to human natures as canyon is to canyons. We would never discuss the "characteristics of canyon." Although all canyons share certain attributes, we always use the plural form of the word when talking about them in general. That's because even though all canyons have more characteristics in common with one another than any canyon has with a painting or a snowflake, we automatically recognize the vast diversity subsumed within the category canyons. As with canyon, at times there is reason to speak of human nature in the singular, as I sometimes do when referring to what we all share -- for example, the ability to communicate in language, the possession of a rich culture, and the capacity to develop complex ethical systems. After all, there are at least near-universal aspects of our natures and our genomes (genetic endowments), and the variation within them is small in relation to the differences between, say, human and chimpanzee natures or human and chimpanzee genomes. I argue, contrary to the prevailing notion, that human nature is not the same from society to society or from individual to individual, nor is it a permanent attribute of Homo sapiens. Human natures are the behaviors, beliefs, and attitudes of Homo sapiens and the changing physical structures that govern, support, and participate in our unique mental functioning. There are many such natures, a diversity generated especially by the overwhelming power of cultural evolution -- the super-rapid kind of evolution in which our species excels. The human nature of a Chinese man living in Beijing is somewhat different from the human nature of a Parisian woman; the nature of a great musician is not identical with that of a fine soccer player; the nature of an inner-city gang member is different from the nature of a child being raised in an affluent suburb; the nature of someone who habitually votes Republican is different from that of her identical twin who is a Democrat; and my human nature, despite many shared features, is different from yours. The differences among individuals and groups of human beings are, as already noted, of a magnitude that dwarf the differences within any other nondomesticated animal species. Using the plural, human natures, puts a needed emphasis on that critical diversity, which, after all, is very often what we want to understand. We want to know why two genetically identical individuals would have different political views; why Jeff is so loud and Barbara is so quiet; why people in the same society have different sexual habits and different ethical standards; why some past civilizations flourished for many centuries and others perished; why Germany was a combatant in two horrendous 20th-century wars and Switzerland was not; why Julia is concerned about global warming and Juliette doesn't know what it is. There is no single human nature, any more than there is a single human genome, although there are features common to all human natures and all human genomes. But if we are trying to understand anything about human society, past or present, or about individual actions, we must go to a finer level of analysis and consider human natures as actually formed in the world. It is intellectually lazy and incorrect to "explain" the relatively poor school performance of blacks in the United States, or the persistence of warfare, or marital discord, by claiming that nonwhites are "naturally" inferior, that all people are "naturally" aggressive, or that men are "naturally" promiscuous. Intellectual performance, aggression, and promiscuity, aside from being difficult to define and measure, all vary from individual to individual and often from culture to culture. Ignoring that variance simply hides the causative factors -- cultural, genetic, or both -- that we would like to understand. Permanence is often viewed as human nature's key feature; after all, remember, "you can't change human nature." But, of course, we can -- and we do, all the time. The natures of Americans today are very different from their natures in 1940. Indeed, today's human natures everywhere are diverse products of change, of long genetic and, especially, cultural evolutionary processes. A million years ago, as paleoanthropologists, archaeologists, and other scientists have shown, human nature was a radically different, and presumably much more uniform, attribute. People then had less nimble brains, they didn't have a language with fully developed syntax, they had not developed formal strata in societies, and they hadn't yet learned to attach worked stones to wooden shafts to make hammers and arrows. Human natures a million years in the future will also be unimaginably different from human natures today. The processes that changed those early people into modern human beings will continue as long as there are people. Indeed, with the rate of cultural evolution showing seemingly continuous acceleration, it would be amazing if the broadly shared aspects of human natures were not quite different even a million hours (about a hundred years) in the future. For example, think of how Internet commerce has changed in the past million or so minutes (roughly two years). As evolving mental-physical packages, human natures have brought not only planetary dominance to our species but also great triumphs in areas such as art, music, literature, philosophy, science, and technology. Unhappily, though, those same packages -- human behavioral patterns and their physical foundations -- are also the source of our most serious current problems. War, genocide, commerce in drugs, racial and religious prejudice, extreme economic inequality, and destruction of society's life-support systems are all products of today's human natures, too. As Pogo so accurately said, "We have met the enemy, and they is us." But nowhere is it written that those problems have to be products of tomorrow's human natures. It is theoretically possible to make peace with ourselves and with our environment, overcome racial and religious prejudice, reduce large-scale cruelty, and increase economic equality. What's needed is a widespread understanding of the evolutionary processes that have produced our natures, open discourse on what is desirable about them, and conscious collective efforts to steer the cultural evolution of the more troublesome features of our natures in ways almost everyone would find desirable. A utopian notion? Maybe. But considering progress that already has been made in areas such as democratic governance and individual freedom, race relations, religious tolerance, women's and gay rights, and avoidance of global conflict, it's worth a try. Paul R. Ehrlich is a professor of population studies and of biological sciences at Stanford University. This essay is adapted from his Human Natures: Genes, Cultures, and the Human Prospect, to be published next month by Island Press. http://chronicle.com Section: The Chronicle Review Page: B7
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Copyright © 2000 by The Chronicle of Higher Education