Darwinian Virtues

Darwin on Man

“Origin of man now proved…. He who understands baboon would do more towards metaphysics than Locke.”¹ With this bold statement, made in a pocket notebook in 1838, Charles Darwin broached the revolutionary research program that would culminate in his two masterworks—the Origin of Species (1859) and the Descent of Man (1871). No aspect of Darwin’s evolutionary theorizing was more controversial than its disturbing implica-tions for humankind. And none has proved to be more fraught with scientific difficulties.

Perhaps the greatest of the conceptual difficulties that Darwin faced was the phenomenon of altruism. In a world evolved according to natural selection, cooperative behavior is a puzzle. This is because natural selection is inherently selfish, promoting adaptations that serve only the individual. The survival instinct of each individual, Darwin asserted in the Origin of Species, “is good for itself, but has never, as far as we can judge, been produced for the exclusive good of others.”² In the Origin, where he largely avoided the topic of humans, and later in the Descent of Man, Darwin wrestled with this issue in ways that never fully satisfied him. So great was his acumen on this difficult problem that he nevertheless managed to articulate, in rudimentary form, each of the three most compelling theories extended by his successors during the next century.

As a first solution, Darwin proposed that natural selection might give rise to altruistic behaviors, such as risking one’s life for another individual, if these behaviors benefited family members. The basis for his solution was that family members generally share the same inherited traits, including any genetic propensities toward giving mutual aid. To the extent that close relatives achieve superior reproductive success as a result of receiving assistance, their offspring will tend to pass on any genes that enhance reproduction—the central mechanism of Darwinian evolution. Darwin also considered the idea of reciprocity among non-kin, concluding that cooperative forms of behavior could arise as long as the favors or benefits that nonfamily members received were reciprocated over the long run. Finally, Darwin considered the possibility of the natural selection of some groups as opposed to others. He reasoned that communities behaving in a cooperative fashion would tend to be more successful than less altruistic communities.

Darwin’s attempts to resolve the problem of altruism were not particularly convincing to most of his contemporaries, who abhorred the materialistic implications of his theories and who saw moral behavior as compelling evidence of a benevolent Designer. Even Alfred Russel Wallace, who co-discovered the theory of natural selection in 1858 while collecting biological specimens in Malaysia, later concluded that the human brain could not have attained its present form solely by natural selection. The mind, Wallace reasoned, was capable of far more impressive feats of intellectual ability than could possibly have been useful to our ancestors living in a state of nature. He therefore embraced that postmodernism of the day—a belief in disembodied spirits—and proclaimed that some higher power must have intervened in the evolution of our species. “I hope,” remarked a disappointed Darwin, “you have not murdered too completely your own and my child.”³ Alas, Wallace and other Darwinian critics muddied the waters sufficiently that, for the next ninety years, natural selection was relegated to the backwaters of explanation within the social sciences.

1.

Darwinism Revitalized

This situation was changed by William Hamilton, a British graduate student in evolutionary biology in the early 1960s. Picking up from where Darwin had left off on the issue of altruism among family members, Hamilton reformulated Darwin’s thinking into the far more powerful notion of “inclusive fitness.” In contrast to fitness calculated as “reproductive success” (the classical Darwinian notion), Hamilton’s expanded measure adds to an individual’s own reproductive success all of his effects on the reproductive success of close relatives, discounted according to the degree of relatedness.

Armed with a knowledge of mathematics and a fortuitous interest in social insects, Hamilton made his case for “kin selection” by drawing attention to a particularly dramatic natural experiment. He showed that the unusually cooperative behavior of Hymenoptera (bees, ants, and wasps) could be explained by haplodiploidy, the peculiar genetic system that characterizes these species. Among social insects, brothers have no father and receive half of their mother’s genes, which is all the genes they have. By contrast, sisters receive two sets of genes—half from their mother and the other half from their father. Because the father’s genes are the same in each daughter, sisters are twins from the paternal point of view.

As a result of this peculiar genetic system in Hymenoptera, sisters share three quarters of their genes. Sisters are also more closely related to one another than they are either to their mother or to their own offspring (with whom they share, in both cases, only one half their genes). As a consequence of being genetically so similar, Hamilton argued, sisters have evolved the highly cooperative behaviors that characterize social insect societies, where workers—all sisters—typically help their mother, and queen, to rear more sisters. Hamilton’s theory also explains why social insects have evolved sterile castes, a phenomenon that cannot be understood according to classic Darwinian theory, based as it is on the notion of individual reproductive success.

Emboldened by Hamilton’s stunning insight, biologists began to explore its implications for animal social behavior. Such well-known scientists as George Williams, Robert Trivers, Richard Alexander, and Edward O. Wilson soon realized that the theory of kin selection explained a host of important problems in animal behavior. Among these problems was parental investment in offspring, which could now be reconceptualized as a special case of the tendency for kin to help close relatives. Similarly, the fact that females tend to be more choosy about their mates than males was also elucidated by Hamilton’s theory. Because females typically make greater physiological investments in their offspring, they incur greater costs from mating than do males, who can generally afford to mate with any female who will accept them.

Behind every story of cooperation in Hamilton’s version of Darwinian theory there usually lurks a subplot involving competition. The specific outcome of such Hamiltonian scenarios depends on the relative costs and benefits of the two strategies. For example, Hamilton’s theory predicts sibling rivalry on the following grounds: because, on average, only half of each offspring’s genes are shared, siblings can be expected to act altruistically toward one another only when the benefits of doing so exceed twice the costs, thus counterbalancing the difference in their genetic relatedness—one half.

An extreme example of sibling rivalry involves the murderous behavior of the baby cuckoo. Female cuckoos surreptitiously lay their eggs in the nests of other birds, a behavior that often succeeds in eliciting parental care by the unsuspecting foster parents. Immediately after hatching, the baby cuckoo ejects any other offspring from the nest. It does so because these step-siblings diminish the cuckoo’s share of parental investment (a cost); they also fail to counterbalance this cost by providing a genetic insurance policy in the form of one half of the baby cuckoo’s own genes. (Because female cuckoos wisely lay only one egg in the nests of other birds, baby cuckoos do not need to distinguish step-siblings from true siblings.)

Of course human beings are nothing like cuckoos or social insects, and the application of Hamilton’s ideas to our own species raises a variety of difficult questions that Hamilton did not try to resolve. To begin with, no one has identified any genes that code for altruistic behavior. Such genes are nevertheless believed to exist because certain aspects of personality that underlie cooperative behavior—for example, empathy, sociability, and even altruism itself—are moderately heritable. When reared apart, identical twins are twice as likely to share personality traits such as empathy, compared with reared-apart fraternal twins, who share only half of their genes.⁴

Applying Hamilton’s ideas to human beings also raises the thorny issues of consciousness and intentions. In dealing with these issues, one must distinguish between genes and the elaborate physiological machinery that genes create in order to further their reproductive interests. Of course genes themselves have no conscious desire to reproduce or to obey Hamilton’s logic about inclusive fitness. Instead, they spread themselves by coding instructions for the building of bodies, which in higher organisms include specialized organs called brains. Brains have evolved by natural selection to give their possessors pleasurable feelings from certain activities—including the taking of nourishment, having sex, and being in the company of friends and family—that are important for reproductive success.

Consider the following example, which contrasts direct and indirect genetic influences. By the logic of inclusive fitness, an individual should be willing to lay down his life for more than two siblings, more than four nieces or nephews, or more than eight first cousins (to paraphrase a famous quip by British biologist J.B. Haldane). Does this Darwinian inference require that people consciously seek to spread their genes via acts of generosity doled out to relatives according to Haldane’s formula? Not at all. Genetic propensities toward altruism are expressed only through the indirect mechanism of the brain, which until recently knew nothing of genes. If we are inclined to help our close relatives, including our children, it is because our brains typically derive happiness from assisting our loved ones, just as our brains tend to make us feel guilty whenever we withhold such assistance.

Because genes operate indirectly via the bodies and brains that they construct with each new generation, human beings engage in many kinds of behaviors—such as adopting a child—that do not necessarily enhance their Darwinian fitness. Most of the children we love and nurture are our own, but this circumstance does not stop some of us from wanting to nurture other children. Brains have also been engineered by natural selection to have a multiplicity of adaptive feelings, some of which conflict. We may like one sibling better than another (perhaps for good reason), and we may therefore give unequal assistance to our siblings because our brains, not our genes, ultimately determine how we respond to the people around us.

2.

Genetic Virtues

Matt Ridley’s new book, The Origins of Virtue, reviews and digests what has been learned about human social behavior during the three decades since William Hamilton’s conceptual breakthrough. A highly respected science journalist and former editor at The Economist, Ridley stands squarely behind the call for Darwinian expansion into the social sciences. One of his principal goals in The Origins of Virtue is “to convince you to try to step out of your human skin and look back at our species with all its foibles.” Under attack is what two leading evolutionary psychologists, John Tooby and Leda Cosmides, have called the Standard Social Sciences Model, which holds that culture largely, or perhaps even entirely, overrides biology in shaping human behavior.⁵

Although most of his book summarizes other researchers’ ideas and findings, Ridley has many original insights of his own to add to the current work in evolutionary psychology. The scope of his approach, and the thoughtfulness of his analysis, are impressive; upholders of the Standard Social Sciences Model will find that they have much to consider. His new book seeks to explain cooperation, aggression, religion, trade, ecological destruction, and even what Ridley conceives to be the best form of government. Lest one surmise that he is a “pop” sociobiologist, he has a doctorate in zoology from Oxford University; his Darwinian viewpoint is similar to that of another Oxford scholar, Richard Dawkins, whose best-selling books about selfish “gene machines” have made him one of the most influential exponents of the logic of natural selection in evolutionary biology. ⁶ Like Dawkins, Ridley has a flair for expressing arcane issues in clear and entertaining prose.

Ridley is hardly a newcomer to the debates over evolutionary psychology. An earlier book, The Red Queen (1993), tackled the evolution of sexuality and is one of the most respected treatments of the subject. Expressed by its title, this previous book’s metaphor for evolution is inspired by Lewis Carroll’s Alice in Wonderland, where the Red Queen explains that she must continually keep moving ahead just to stay in the same place. As with the predicament of the Red Queen, evolution involves an arms race between organisms and their enemies, which endlessly transform themselves just to stay competitive. Following other recent biologists, Ridley argues that sexual choices and strategies have evolved to keep pathogens, such as bacteria and viruses, off balance. By continually shuffling their genetic deck of immunological locks, sexual organisms are attempting to foil the pathogens’ latest molecular keys. For example, a pathogen may have evolved the ability to attach itself to a particular cellular receptor, enabling it to penetrate the cell wall and cause illness. Sexual recombination of the host’s genes during reproduction continually changes these molecular locks, blocking the pathogen’s previous method of entry.

The Origins of Virtue takes up where The Red Queen left off, namely, with Homo sapiens. Unafraid of confronting difficult problems, Ridley has devoted his latest book to the paradox that so troubled Darwin: If inherited dispositions, which have evolved by natural selection, are always in the service of the individual, then why is cooperation observed in nature? The book is organized on three different levels: genes, social behavior, and theories about social behavior. Ridley begins his story with genes. In higher organisms, he explains, genes have teamed up as chromosomal “parliaments,” which in turn have teamed up as cells, which subsequently evolved into creatures with specialized organs. But why have genes—which, according to selfish gene theory, care only about reproducing themselves—entered into such complex cellular alliances?

The answer involves Hamilton’s notion of inclusive fitness, along with Adam Smith’s insight into the division of labor. Cells, on this view, are to be seen as “close relatives” because they possess identical genes, a circumstance that encourages them to act altruistically whenever cooperative actions enhance their ability to have descendants. The division of labor facilitates this outcome by allowing specialized cells to do their tasks more efficiently than generalist cells. For example, cells that are specialized for digesting food make more efficient use of available nutrients, and well-fed organisms tend to have more offspring.

Potential conflicts continually arise between genes, even within the same cell, because genes, rather than cells or whole organisms, are the primary replicators of life. These potential conflicts must be suppressed, Ridley explains, in order to keep genetic parliaments working together. Consider pregnancy—usually understood as a wonderfully harmonious relationship between mother and fetus. From a Darwinian perspective, pregnancy is nothing of the kind. The fetus, which has genes from both father and mother, is twice as related to itself as it is to its mother, so it is inclined to act selfishly with regard to how much sustenance it ought to receive from its mother. In demonstrating this tendency, David Haig, a biologist working at Harvard University, has documented how fetal cells invade the main artery supplying blood to the placenta, killing the artery’s muscle cells. The goal of these killer fetal cells is to usurp control of the blood supply from the mother. The fetus also secretes human placental lactogen (hPL), a hormone that blocks the effects of insulin and thereby increases the amount of glucose in the mother’s blood.

The fetus is actually pursuing a precarious strategy, attempting to reduce the mother’s energy stores at the expense of future siblings, but not to the extent that the mother cannot successfully breast-feed following the birth. Because the mother is equally related to all of her offspring, she prefers to retain more of her energy reserves for future offspring and resists the fetus’s selfish efforts by secreting ever higher levels of insulin. Moreover, the gene that codes for the fetus’s production of hPL turns out to be inherited from the father, not the mother, whose biological interests are ill served by this inimical substance. Indeed, the fetus can be considered a “paternal parasite” growing inside the mother.

From an evolutionary perspective, pregnancy is thus the story of steady escalations in selfish fetal actions followed by equally selfish maternal reactions. Usually this arms race is evenly balanced (owing to the Red Queen effect), and pregnancy runs its normal course. But sometimes there are complications. When expectant mothers suffer from high blood pressure and gestation diabetes, these are often medical instances in which the tug-of-war has become dangerously imbalanced in favor of the fetus. Thus maternal investment in the fetus—itself a special case of altruism toward close relatives—is plagued by continual conflicts based on the differing genetic interests of mother and offspring. These and other fascinating biological findings are reviewed by Ridley as he documents how genetic cooperation risks occasional rebellion on the part of inherently selfish genes.

It is easy for Darwinians to explain cooperation between cells, because cells almost always are genetically identical to one another within the same organism. Similarly, cooperation between close genetic relatives is explained by Hamilton’s theory of inclusive fitness. But why does cooperation occur among unrelated organisms? One of Darwin’s seminal ideas has again provided modern biologists with the critical stimulus. In the early 1970s Robert Trivers, a brilliant young biologist at Harvard, revamped Darwin’s speculations about reciprocal altruism using a formal cost-benefit approach to the problem.

Ridley illustrates this theory with a vivid biological example first identified by Trivers. “Cleaner-fish” live in coral reefs, where they boldly enter the mouths of larger “client-fish” to remove parasites. Remarkably, client-fish do not eat their cleaners. This behavioral relationship is dependent on an inherited disposition, because client-fish raised in isolation (and accustomed to gobbling up smaller fish for dinner) will instinctively open their mouths for cleaning the very first time they encounter a cleaner-fish. Cases like that of the cleaner-fish demonstrate that cooperation can evolve among unrelated organisms as long as there is mutual benefit. Used in conjunction with Hamilton’s theory of kin selection, the idea of reciprocal altruism has greatly increased the scope of Darwinian approaches to cooperative behavior and is especially important for understanding primate social behavior.

In the early 1970s, work on reciprocal altruism was combined with the study of game theory, introduced from the field of economics. Much of Ridley’s story is built around this fruitful episode of intellectual cross-fertilization. At the heart of his account is the well-known game called the prisoner’s dilemma. Two prisoners—both implicated in the same crime—are given a chance to lighten their sentences by testifying against each other. They are kept in separate cells and cannot communicate. Without their testimony, the authorities can convict them only on a lesser charge, punishable by two years in prison. By giving evidence, an informant can avoid doing jail time, but his partner’s sentence will be increased to ten years. If both prisoners remain silent, they are collectively better off than if both defect; but each is individually better off if he defects, no matter what the other one does. The “rational” choice, then, is always to defect—or so asserted the economists through the 1970s.

As game theorists became increasingly intrigued by the prisoner’s dilemma during the 1970s, they set about transforming the predicament to make it more lifelike. For example, theorists altered the rules so that people could play the game more than once. Players were also allowed to communicate with one another during the game. Under such conditions, researchers found that experimental subjects were much more willing to cooperate, a result that some economists initially dismissed as evidence of “irrational” behavior, given that the “rational” choice in the prisoner’s dilemma is always to defect. In 1979, the political scientist Robert Axelrod sponsored a computer tournament for games similar to the prisoner’s dilemma. To everyone’s surprise, the tournament was won by the simplest of all the programs submitted. Called “Tit-for-tat,” the victorious program always began by cooperating with its competitor programs and then faithfully repeated whatever the other programs had last done.

One of Ridley’s most dramatic examples from natural behavior helps to illustrate the virtues of this strategy. In Central America, vampire bats feed at night on the blood of large animals. Not every bat is successful in finding a meal. Without blood, a bat can starve to death in about three days. Vampire bats have solved this problem by resorting to conditional cooperation. Back in their dens, bats who have found a meal during the night regurgitate blood into the mouths of bats who have not. Recipients of these nightly favors tend to return them on subsequent nights to those bats who have fed them in the past. Conversely, bats often refuse another bat who has denied them in the past. The key to this bit-for-bat process is the individual bat’s ability to remember the history of its relationships with all other bats living in its den. This mnemonic requirement has driven the evolution of vampire bat brains, which possess the largest neocortex of all known bat species.

The story of vampire bats underscores an important part of Ridley’s argument. Evidence for reciprocal altruism is relatively rare in animals, with the exception of dolphins, porpoises, and our closest primate relatives. Memory for past actions—and hence the ability to discriminate between past altruists and defectors—requires a large brain. Among social animals, there is a direct correlation between the size of the neocortex and the size of the typical group. Human beings are consistent with this general trend, possessing the largest neocortex and also living in the largest social groups of any primate.

3.

Nature versus Nurture

There is ample evidence that humans cooperate with people to whom they are not closely related—more so than for any other species. Following his relentless Darwinian logic, Ridley attributes these cooperative tendencies to an innate propensity toward “virtue.” This claim would obviously be false were it about unconditional virtue. Humans, however, have evolved dispositions to cooperate or compete that take their cues from the actions of other individuals. In positing an innate but contingent tendency toward virtue, Ridley is fully aware that many aspects of human behavior can be explained just as well by social learning as by genetic predisposition. He also notes that the two explanations are not mutually exclusive. “For human beings,” he acknowledges, “you can never entirely reject the culture hypothesis.” Ridley further cites Daniel Dennett’s argument that ingenious adaptations, if they are really that good, “will be routinely rediscovered by every culture, without need of either genetic descent or cultural transmission of the particulars.”⁷ Sociobiologists, for example, have sometimes claimed that humans possess a territorial instinct. But the need for defending a territory against rival groups makes so much sense that humans may have repeatedly adopted the practice based on cultural traditions passed down through the generations.

What evidence, then, does Ridley present to support his claim about cooperative instincts? Some of this evidence involves the kind of “just-so” stories that sometimes invite accusations of circular reasoning from critics of sociobiology and evolutionary psychology. There is a big difference, however, between adaptationist stories that are used as guides to testable evolutionary hypotheses and ad hoc stories invented solely in order to bolster untested claims. Without independent evidence, it is a just-so story that “the eye has evolved for seeing.” But based on convincing morphological evidence of the way eyes developed from cells vaguely sensitive to light to organs capable of seeing, this adaptationist story turns out to be true for more than forty different evolutionary lineages, from arthropods to vertebrates.

What is impressive about Ridley’s argument is the fact that his phylogenetic account of cooperation is strengthened by at least three independent lines of evidence. The first comes from neurobiology. Some people with brain injuries to the prefrontal lobe display a peculiar cognitive deficit: they are emotionally unresponsive. Yet these patients can generally reason like anyone else, and suffer no deficiencies in memory or intelligence. These people are unable, however, to make decisions about simple matters. Their broken brains trap them in endless rational debates about pros and cons.⁸ Emotions have an important role in decision making because our reasoning abilities evolved in tandem with the visceral reactions that reinforce our ability to distinguish fair from unfair.

A second line of relevant evidence involves recent research on cognitive functioning. As Darwin himself understood a century ago, some of the most persuasive evidence for evolution involves manifestations of imperfect design. For sociobiologists such as Ridley, it is always expedient to be able to show that, in engineering the architecture and functioning of our brains, a wise Creator could have done a much better job than the forces of evolution. Evolutionary solutions tend to reflect the unplanned nature of evolutionary change, as well as the inability of evolution to anticipate the future. Humans are no exception to this rule and display evidence of poor cognitive design: we are not very good at certain types of abstract reasoning. Given the task of figuring out a simple mathematical formula that determines a sequence of numbers, experimental subjects typically fail to employ the logic of falsification, which is the most efficient way to reach the correct answer. When the task is recast as an exercise in detecting whether someone has violated a social contract (such as agreeing to provide a service in return for a specific remuneration), people suddenly reason more proficiently, focusing on evidence that would clearly establish that the other person is cheating.⁹

Similar research has prompted economists such as Robert Frank to recognize that economic behavior cannot be explained solely by rational choice. Instead, trust, guilt, and an occasional desire for revenge all play an important role in economic decisions. (One may wonder why economists were so late in coming to a conclusion that many of us think is self-evident, but we should bear in mind that a tendency to prefer rational explanations for human behavior has been dear to Western thinking since the Scientific Revolution.) A third line of evidence, which Ridley oddly overlooks, is also pertinent to his argument about innate virtue. As I have previously mentioned, twin studies have shown that altruistic tendencies are heritable, which strongly suggests that they have evolved by natural selection.¹⁰

Ridley’s treatment of game theory, and its special relevance to cooperative behavior, sets the stage for the last half of his book. There he successively treats tribal tendencies, war, trade, environmental destruction, and finally the proper role of government. This latter part of the book revolves around questions that political philosophers have asked themselves for centuries. Are human beings noble savages who were subsequently corrupted by civilized life (Rousseau’s view), or are we innately selfish and in need of a Hobbesian Leviathan to curb our unruly desires? Ridley rejects this hackneyed dichotomy. Our genes may be the mechanisms by which our reproductive interests are selfishly achieved, but they go about achieving these interests through genuinely cooperative behavior. For Ridley, the deed is what ultimately counts. Because of our innate propensity to cooperate, Ridley argues, we are a “groupish” species with basically good intentions. But groupishness entails a Faustian bargain, namely, our tendency to engage in “tribal thinking.” Because we are both capable of cooperating and, in his view, are hard-wired to be wary of defectors, we tend to trust those people whom we know well. Such trust was originally limited to the band or tribe, which is no longer the case today. Still, strong group loyalties often distinguish the people we trust from those we do not, and thus underlie our regrettable tendency toward xenophobia.

Group loyalties are maintained, Ridley argues, by the human inclination toward conformity, which is more pronounced than in any other primate. We tend to conform because we place high value on the opinions of others and especially covet our reputations for trustworthiness and allegiance to the group. Religions, in particular, tend to stress “in-group” versus “out-group” thinking, intensifying our groupish tendencies. Although religions emphasize the importance of cooperation among true believers, they also tend to stir up animosity between true believers and nonbelievers. Even Christianity, with its noble ethos of “love thy neighbor,” has been the cause of many deadly crusades against non-Christian groups. Similarly, during the Reformation, Catholics thought it was their solemn duty to burn reform-minded Protestants as heretics.¹¹

One weakness in Ridley’s argument involves his failure to discuss in sufficient detail just how genetic explanations of cooperation and xenophobia can be reconciled with evidence of dramatically changing social attitudes over time. During wars, for example, ethnic and national groups have regularly pushed xenophobia to genocidal extremes, as occurred in Nazi Germany, and as goes on today in Bosnia, Rwanda, and other parts of the world. But Germany and some of its former enemies are now loyal allies, and the same can be said of Japan and the United States. Although such evidence is not a fatal blow to Ridley’s argument, these kinds of historical transformations call for analysis of how historical and cultural experiences within different social groups lead to cooperation rather than xenophobia. Human beings seem equally capable of both strategies, so genetic dispositions are never the full story (as Ridley would agree).

One contingent mechanism that Ridley does discuss in this connection is social exchange. Because humans appreciate the advantages deriving from the division of labor, we often exchange goods with our closest neighbors. Archaeological evidence suggests that trade is an ancient proclivity, dating back at least two hundred thousand years (based on the considerable distances that stone tools traveled from their quarries). Even the fierce Yanomamo of Venezuela, Ridley notes, maintain strong village alliances that owe much of their durability to trade.

In one of the most interesting chapters of his book, Ridley addresses the issue of environmental devastation, which he recasts as a version of the prisoner’s dilemma. We would all be better off if we agreed not to overexploit our environment. Yet we generally do so anyway, given that the other guy is likely to beat us to it; and so arises the “tragedy of the commons.” When a Pleistocene hunter finally killed the last woolly mammoth to feed his hungry family, he would have been foolish to spare this mammoth’s life only to see his loss become someone else’s gain. The record of mass extinctions during the late Pleistocene points strongly to overhunting by man, with 73 percent of the large mammals disappearing within a few thousand years of Homo sapiens’s colonization of the New World. Similar waves of mass extinction among flightless birds and mammals followed the arrival of humans in Madagascar, Australia, New Zealand, and the Polynesian islands.

Still, according to Ridley, responsible ecological stewardship is possible owing to our predilection for cooperative behavior. The key, he claims, is private ownership of property. Ridley reviews a wide variety of examples—from Maine lobstermen to Nepalese rice farmers—to show that people tend to protect their environments whenever they can control its resources and also appreciate the consequences of their own excesses. His most convincing example involves the conservation of big game in Africa. Most government efforts to eliminate poaching for ivory and bush meat have been “an unmitigated disaster,” Ridley asserts. In Zimbabwe, however, the title to wildlife has been given back to local communities, which allow sport hunters to bid for the right to shoot wild game. Villagers now work hard to protect their wildlife from poachers, and the Zimbabwe program has been a big success. Unfortunately, many cases of environmental management do not have such happy outcomes, and Ridley’s provocative treatment of this subject is too incomplete to be convincing.

Ridley concludes his book with a chapter “in which the author suddenly and rashly draws political lessons.” Building on his argument about ecological stewardship, Ridley argues that the best government is one that devolves responsibilities back to the private sector, in the style of Margaret Thatcher’s Britain. Ridley has an occasional tendency to offer glib generalizations about complex issues, and this tendency is particularly apparent in his final chapter. For example, many of the world’s most pressing environmental problems, such as global warming and ozone-shield depletion, call for international solutions, not local ones. Ridley does not distinguish between these rather disparate ecological problems or show clearly just when private solutions are preferable to those involving government action.

4.

Contrasting Sociobiological Faces

“Sociobiology has two faces,” the philosopher of science Philip Kitcher asserted a decade ago in his critical review of the field. “One looks toward the social behavior of nonhuman animals. The eyes are carefully focused, the lips pursed judiciously. Utterances are made only with caution. The other face is almost hidden behind a megaphone. With great excitement, pronouncements about human nature blare forth.”¹² Which face does Matt Ridley show us in The Origins of Virtue? The answer to this question depends, in part, on which chapter of his book we are considering. One of Ridley’s distinct merits as a scholar is that he understands the difference between speculation and science; he almost always identifies which is which, and also asks whether scientific claims have been adequately tested. Still, my overall impression is that Ridley did somewhat better in The Red Queen in acknowledging points of uncertainty and in stressing rival interpretations of data, probably because more is known about the biology of sex than about human social behavior, which inevitably requires us to unravel the complex interplay of genetic predispositions and historically contingent experiences.

From reading Ridley’s new book, it is nevertheless clear that evolutionary approaches to human behavior have made impressive empirical headway during the last twenty years. As Ridley’s sweeping survey demonstrates, this research program now represents a highly interdisciplinary effort that unites evolutionary biology, behavioral genetics, neurobiology, anthropology, medicine, economics, game theory, psychology, and history—to mention only the most important of the contributing disciplines. It is perhaps no accident that science journalists such as Ridley have become almost indispensable in keeping scientists themselves abreast of this sprawling enterprise. ¹³ In addition, this rich interdisciplinary approach has created far greater opportunities for establishing truth by empirical convergence.

One last point is worth making in connection with Ridley’s thoughtful and provoking book, and especially with regard to ongoing controversies over the Darwinian perspectives it advocates. In this often heated debate, it does not really help for adversaries to argue about whether human behavior is genetically or culturally determined (it is both); about whether human consciousness invalidates the effects of natural selection (consciousness is natural selection’s most remarkable product, not its antithesis); about whether Darwinian theory robs us of our free will (it clearly does not); or about whether Darwinians can be usefully divided into narrow-minded “ultras,” who attribute everything to natural selection, and open-minded “pluralists” (they cannot be so divided). Critical empiricism, not debating skills on either side, will ultimately resolve these controversies. As Charles Darwin taught us more than a century ago, openness to diverse lines of evidence and a dogged dedication to hypothesis testing are the enduring Darwinian virtues.