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Darwinian Virtues

The Origins of Virtue: Human Instincts and the Evolution of Cooperation

by Matt Ridley
Viking (To be published in paperback by Penguin in April 1998.), 295 pp., $24.95

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.


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.


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.

  1. 1

    Paul H. Barrett, Peter J. Gautrey, Sandra Herbert, David Kohn, and Sydney Smith, editors, Charles Darwin’s Notebooks, 1836-1844: Geology, Transmutation of Species, Metaphysical Enquiries (Cornell University Press, 1987), p. 539.

  2. 2

    Charles Darwin, On the Origin of Species by Means of Natural Selection (London: John Murray, 1859), p. 210.

  3. 3

    Charles Darwin, More Letters of Charles Darwin (London: John Murray, 1903), 2:39 (letter of March 1869).

  4. 4

    John C. Loehlin, Genes and Environment in Personality Development (Newbury Park, California: Sage, 1992), pp. 57-59.

  5. 5

    John Tooby and Leda Cosmides, “The Psychological Foundations of Culture,” in Jerome Barkow, Leda Cosmides, and John Tooby, editors, The Adapted Mind: Evolutionary Psychology and the Generation of Culture (Oxford University Press, 1992), pp. 19-136.

  6. 6

    Richard Dawkins’s major publications include The Selfish Gene (1976), The Extended Phenotype (1982), The Blind Watchmaker (1986), River Out of Eden (1995), and Climbing Mount Improbable (1996).

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