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Wonderful Life: Debating Evolution in the Age of DNA

ISSUE:  Spring 2004

Francis Crick winged into the Eagle, a pub popular with researchers at Cambridge University’s nearby Cavendish Laboratory, boasting to one and all, “We have found the secret of life.” It was early in 1953, and the “we” referred to thirty-six-year-old British biophysicist Crick and twenty-four-year-old American biochemist James D. Watson, then working at the Cavendish on a postdoctoral fellowship. Watson reported feeling “slightly queasy” at Crick’s boast, but over the next few decades, many biologists came to see it as fully justified. In one of the great “eureka” experiences of modern science, Watson and Crick had discovered the gene’s double-helical structure by brilliantly and rapidly combining the findings of others with insights of their own. This surprisingly simple, highly elegant structure shed new light on the mechanics of evolution by suggesting how genetic reproduction, inheritance, and variation operated at the molecular level.

Although the gene stood at the heart of the modern synthesis, it was a black box prior to 1950. Until then, many scientists envisioned the gene as a complex assemblage of proteins that would take decades to decipher. Yet a growing body of evidence suggested that a much simpler macromolecule, deoxyribonucleic acid (or DNA), carries hereditary information. Watson and Crick followed the latter trail, and it led them to glory. They found that DNA is structured somewhat like a twisted railroad track with sturdy rails along its outer edges and a sequence of connecting ties, each composed of one of two different pairings of four base molecules commonly identified by their initials: A, T, G, and C. If DNA splits lengthwise, then each half replicates the whole by attracting new pairs for its remaining bases from the cell’s organic soup, A to T and G to C. The macromolecule carries genetic information in the sequence of its base molecules, which serve as a template for forming ribonucleic acid (or RNA) and, in turn, proteins. Information flows only one way in this mechanism—from the DNA to the proteins that construct the organism, never from the organism back to the DNA. The result nicely matches the neo-Darwinian principle that inborn hereditary information guides individual development without any gene-altering feedback from the environment. In these and other respects, DNA structure provides a serviceable molecular foundation for evolution to proceed in a manner fitting the modern synthesis. Both concepts are starkly materialistic and functionally reductionist. Still, tensions developed between molecular biologists and neo-Darwinian evolutionists.

Watson and Crick did not work out all the implications of DNA structure themselves. In their initial 1953 papers, they simply noted that it “immediately suggests a possible copying mechanism for the genetic material,” which they spelled out in some detail, and that “spontaneous mutations may be due to a base occasionally occurring in one of its less likely tautomeric forms.” These and other implications inspired a generation of scientists to pursue molecular biology. Traditional ways of studying evolution suddenly seemed terribly old-fashioned. “For those not studying biology at the time in the early 1950s, it is hard to imagine the impact the discovery of the structure of DNA had on our perception of how the world works,” zoologist Edward O. Wilson later recalled. “If heredity can be reduced to a chain of four molecular letters—granted, billions of such letters to prescribe a whole organism—would it not also be possible to reduce and accelerate the analysis of ecosystems and complex animal behavior?”

Watson and Wilson, who became two of the most influential scientists of the late 20th century, both joined Harvard’s biology department as assistant professors in 1956. Watson led the shock troops for the newer forms of molecular biology. Wilson, who studied ants, upheld the older naturalist tradition associated at Harvard with zoologist Ernst Mayr, an early proponent of the modern synthesis. The two young biologists rarely spoke to each other during their years together at Harvard. Their department, in a microcosm of larger developments within the profession, eventually split into separate ones for molecular and evolutionary biology. Wilson later described Watson as “the most unpleasant human being that I had ever met.” Their relationship worsened after Wilson (whom Watson regarded as a mere bug collector) received tenure before Watson. Mayr, Wilson, and others in their camp viewed molecular biology as too narrow and limited to comprehend all aspects of the evolutionary process. To them, organisms and ecosystems still mattered. For his part, in the best-selling book The Double Helix, Watson dismissed most zoologists and botanists of the 1950s as “a muddled lot [that] wasted their efforts in useless polemics about the origin of life.” Geneticists of the era fared little better in Watson’s account. “You would have thought that with all their talk about genes they should worry about what they were,” he wrote. “All that most of them wanted out of life was to set their students onto uninterpretable details of chromosome behavior or to give elegantly phrased, fuzzy-minded speculations over the wireless on topics like the role of the geneticist in this transitional age of changing values.” Yet over time, and from their separate departmental homes, evolutionary and molecular biology grew to complement and reinforce each other.

At the elemental level, the discovery that all species (even the most primitive unicellular ones) shared a common genetic code suggested that they have a common ancestry. In turn, the comparative study of DNA from various organisms elucidated their evolutionary relationships. In one spectacular example of this from the 1960s, modern sythesis architect Theodosius Dobzhansky’s protégé Richard C. Lewontin used a technique called “gel eletrophoresis” to measure genetic variation among individuals of the same species. This analysis tested his mentor’s hypothesis that enough latent variability exists in recessive alleles to feed the evolutionary process in response to changed environmental conditions without added mutations. Lewontin found what he was looking for—indeed, he found so much genetic variability within species that much of it must have little or no effect on individuals. Taking the position that all the variation may be meaningless, die-hard opponents of Dobzhansky’s hypothesis clung to the classical view (historically associated with geneticists Thomas Hunt Morgan and Hermann Muller) that mutations feed evolution.

Further, Watson’s success in reducing much of biology to molecules inspired even his adversaries. “He and other molecular biologists conveyed to his generation a new faith in the reductionist method of the natural sciences,” Wilson later noted. “A triumph of naturalism, it was part of the motivation for my own attempt in the 1970s to bring biology into the social sciences through a systematization of the new discipline of sociobiology.” Watson came to appreciate Wilson’s work in sociobiology—and it helped mend their relationship in the years after Watson left Harvard to run the Cold Spring Harbor genetics laboratory, a traditional center for research in applied human genetics dating from the heyday of eugenics. Yet Wilson never took a molecular approach to sociobiology. Indeed, his initial foray into the field grew out of his interest in how insect colonies function, which he pursued in opposition to the molecular focus of biologists who followed in Watson’s wake. Early on, for example, Wilson explored the impact of population size and density on the caste system of ant colonies and on aggressive behavior by various types of “social animals” (animals that live in groups). Molecules alone could not explain these developments, he argued.

Instead, the fundamental breakthrough to sociobiology came in a brilliant two-part 1964 article by William D. Hamilton, a British graduate student who also rejected the molecular approach to biology. As a self-proclaimed disciple of the legendary population geneticist Ronald Fisher, Hamilton focused his powerful intellect on interactions among genes rather than on the gene’s molecular composition. Here, he believed, lay the true secret of life. While still a college student at Cambridge during the 1950s, Hamilton later wrote, “I was convinced that none of the DNA stuff was going to help me understand the puzzles raised by my reading of Fisher and J.B.S. Haldane or to fill the gaps they had left. Their Mendelian approach had certainly not been outdated by any new findings.” Ultimately, Hamilton exceeded even Fisher in seeing evolution (as he put it in his 1964 article) “from a gene’s point of view,” and he inspired Wilson and other sociobiologists to do so as well.

The origins of altruism stood out as the most prominent evolutionary puzzle unsolved by the synthetic theorists. They had melded Darwinism and Mendelism without accounting for self-sacrifice. This left a glaring gap. Critics of selection theory had long pointed to altruistic behavior (particularly by humans) as evidence that a Darwinian struggle for existence could not explain all aspects of life. If nature selects solely for traits leading to an individual’s survival or reproductive success, as classical Darwinism suggested, then self-sacrifice (except to aid one’s own descendants) must have a supernatural source. Such thinking led prominent Darwinists from Alfred Russel Wallace through David Lack to reserve space for the spiritual within their science. Darwin held out for a naturalistic explanation for altruism but never devised a wholly satisfactory one. Although he otherwise thought that selection acted among individuals, here Darwin bowed to group selection. Altruism aids the group at the expense of the individual, he reasoned, as when a bird warns the flock of approaching predators by a self-endangering cry or when childless soldiers die for their country. Castes of sterile worker ants, wasps, and bees present even more dramatic examples of self-sacrificing social behavior. Inasmuch as such traits promote the group’s survival, Darwin noted, perhaps nature selects groups that possess them. Unless members of the group jointly learn and pass along such traits in a Lamarckian manner, however, those traits should fail because single individuals displaying them would tend to die earlier than others. In short, as a randomly generated inborn trait, altruism should not persist. Such thinking led Darwin to admit an element of Lamarckism into his system—but the modern synthesis rejected this solution.

Hamilton proposed a purely Darwinist account for altruism by shifting the level of selection to the gene. Take social insects, he proposed. Because of the peculiar way they reproduce, female ants, wasps, and bees share more genes in common with their sisters (75 percent) than with their own children (50 percent) or brothers (25 percent). Thus, from the gene’s point of view, female ants achieve greater reproductive success by aiding their sisters than their offspring. Fitting the model, all sterile worker ants are female and, as Hamilton noted, “working by males seems to be unknown in the group.” Similarly but less spectacularly, any animal (including a human) that shares genes with its collateral kin (as well as with its lineage) can maximize the survival of those genes by sacrificing for its relatives, provided the number of genes held in common by those relatives exceeds the number lost by its sacrifice. In his 1964 article, Hamilton worked out the algebra of such so-called “kin selection” to show that, at least in theory, it could account for apparently altruistic behavior in terms of selfish genes. “In the world of our model organisms,” he concluded, “we expect to find that no one is prepared to sacrifice his life for a single person but that everyone will sacrifice it when he can thereby save more than two brothers, or four half-brothers, or eight first cousins.” Genetic tendencies in this direction should survive and spread. In this manner, a starkly naturalistic struggle for existence could lie at the heart of seemingly selfless acts of individual love. With this conceptual breakthrough, the way seemed open to find biologic bases for all manner of human and other animal behavior.

Wilson first read Hamilton’s paper in 1965, on a train trip from Boston to Miami. By his own account, Wilson left New England with a casual interest in Hamilton’s ideas, became increasingly “frustrated and angry” about them during the journey, but arrived in Florida fully convinced. “Because I modestly thought of myself as the world authority on social insects,” Wilson related, “I also thought it unlikely that anyone else could explain their origin, certainly not in one clean stroke,” but Hamilton had. Like Hamilton, Wilson believed that whatever explained the behavior of social insects also shed light on the behavior of other social animals, including humans. A core group of evolutionary biologists agreed. An outburst of research ensued, testing and extending Hamilton’s insight and other sociobiologic theories (collectively called “evolutionary psychology” when applied to humans). These efforts sought to explain behavior in terms of its impact on the survival and reproductive success of genes and individuals. Models, metaphors, and concepts proliferated, such as reciprocal altruism (where organisms evolve to help one another survive), evolutionarily stable strategies (where a balance of behaviors within a population serves individual interests), and the arms race (where predator and prey evolve in response to one another’s developments). By factoring in circumstances impacting populations, sociobiologists used such theories to predict and explain all manner of animal behavior.

Wilson pulled many of these threads together in his 1975 survey, Sociobiology: The New Synthesis. Because of its emphasis on adaptations aiding reproduction, the book featured biologic accounts of gender-based behaviors. Males naturally tend to spread their ample sperm (for instance, by having multiple mates), Wilson suggested, while females tend to conserve their scarce eggs (by investing heavily in mate selection and child-rearing). Indeed, some sociobiologists accounted for aggressive behavior by young males as a genetic holdover from a time when it carried reproductive benefit. Among chimpanzees, for example, the most sexually aggressive males produce the most offspring. To some readers, such explanations sounded like justifications for traditional gender roles and sociobiology seemed to endorse the social status quo (or worse)—especially given Wilson’s insistence that humans disregard nature at their peril.

Characteristically, the chapter of Sociobiology dealing with human behavior opened with a deliberately provocative challenge. “Let us now consider man in the free spirit of natural history,” Wilson wrote. “In this macroscopic view the humanities and social sciences shrink to specialized branches of biology; history, biography, and fiction are the research protocols of human ethology; and anthropology and sociology together constitute the sociobiology of a single primate species.” Ethics, he suggested, should “be removed temporarily from the hands of the philosophers and biologicized.” These were bold claims for a discipline supposedly chastened by the excesses of Social Darwinism, eugenics, and Nazi race theory. Wilson did not assert that nature alone shaped human behavior, but he clearly wanted to push the pendulum back from the extreme “nurture” position taken by most mid-20th-century social scientists. They envisioned human culture as infinitely malleable for good or ill, while he declared that “the gene holds culture on a leash.”

The reaction came swiftly. Steeped in environmentalism, many social scientists and humanists hotly contested Wilson’s claims, with protesters once going so far as to pour ice water on him during an academic address. Following the lead of Darwin’s stauchest supporter T. H. Huxley, who in 1893 called it a “fallacy” to base ethics on evolution, many biologists had conceded the study of human behavior to the social scientists. “Culture is acquired, not transmitted through genes,” Dobzhansky assured anthropologists in 1963. Beginning in 1975, Dobzhansky’s former student and Wilson’s colleague, Richard Lewontin, led the scientific assault on sociobiology. Another distinguished Harvard evolutionist with a popular following, paleontologist Stephen Jay Gould, joined the attack. Both acknowledged that genetic determinism offended their Marxist ideology, just as it had offended Dobzhansky’s Christian beliefs, but they focused their criticisms on Wilson’s science. Likening sociobiologic explanations of human behavior to Rudyard Kipling’s Just So Stories of how primitive peoples account for animal origins, Lewontin and Gould damned sociobiology as scientifically flawed and socially dangerous. “Wilson joins the long parade of biological determinists whose work has served to buttress the institutions of their society by exonerating them from responsibility for social problems,” they wrote in a 1975 critique of Sociobiology cosigned by a dozen other Boston-area academics.

Wilson replied with an expanded defense of human sociobiology in his award-winning 1978 book, On Human Nature. The sparring continued into the 21st century, with Wilson gradually gaining allies among evolutionary biologists and a new generation of social scientists. “Overall,” he boasted in the foreword to a commemorative twenty-fifth anniversary edition of Sociobiology, “there is a tendency at the century’s close to accept that Homo sapiens is an ascendent primate, and that biology matters.” Indeed, by offering edgy, materialistic explanations for human interactions, sociobiology and gene-centered evolutionism attracted a popular (as well as an academic) following. It fit the secular, consumer-oriented culture commonly associated with America in the 1980s. Although books by Wilson on the topic sold well, they were eclipsed on both sides of the Atlantic by those of a younger British evolutionist, Richard Dawkins, who as an Oxford student in the late 1960s had taken Hamilton as his “intellectual hero.”

In his intoxicating prose, Dawkins popularized Hamilton’s vision of organisms (including humans) as elaborate apparatuses evolved to propagate their genes. “We are survival machines—robot vehicles blindly programmed to preserve the selfish molecules known as genes,” he explained. “This is a truth which still fills me with astonishment.” The genes themselves cannot plan ahead or respond to their environment, Dawkins stressed. They simply reproduce themselves with occasional random mutations that may or may not assist their survival, and we (“climbing Mount Improbable” in population geneticist Sewall Wright’s adaptive landscape over some four billion years of trial-and-error organic evolution) are the result. Dawkins found this view of life exhilarating. For him, it freed humans from the burden of purposeful design in nature, which he identified as “the most influential of the arguments for the existence of God.” Unlike the controlling purposes of a designing God, Dawkins noted, “Natural selection, the blind, unconscious, automatic process which Darwin described, and which we now know is the explanation for the existence and apparently purposeful form of all life, has no purpose in mind.” By banishing the argument for God from design, he proclaimed, “Darwin made it possible to be an intellectually fulfilled atheist.”

Agreeing with Dawkins’s naturalistic gospel as far as it went, Wilson nevertheless hoped for something more from scientific materialism. “It presents the human mind with an alternative mythology that until now has always, point for point in zones of conflict, defeated traditional religion,” he stated. “Its narrative form is epic: the evolution of the universe from the big bang … [to] life on earth.” Reared in the Bible Belt of Alabama by fundamentalist parents, Wilson maintained that people need to believe in something larger than themselves to justify the individual sacrifices that propagate genes through kin selection. Indeed, in an article coauthored by Darwinian philosopher Michael Ruse, Wilson described religion (or at least ethics based on religion) as “an illusion fobbed off on us by our genes to get us to cooperate.” As people shed spiritual belief in the light of scientific understanding, he believed that some other source of larger meaning must take its place. In his 1998 book Consilience and elsewhere, Wilson offered evolutionism as a new “sacred narrative” capable of enshrining essential ethical principles calculated to advance human development and preserve genetic diversity. Although Wilson’s vision of a naturalistic religion based on modern evolutionary thought stirred widespread comment, most scientists kept their professional distance. “He is a good and gentle man, generous to a fault, with a real concern for … biodiversity and ecological preservation,” Ruse noted. “But I do not see that his fellow evolutionists have to follow him in making a religion out of their shared science.”

Of course, scientists can see their science as important without making it their religion. Certainly most evolutionary biologists viewed the theory of evolution as extremely important: That is why they studied it. Hamilton, for example, like Fisher and eugenics pioneer Francis Galton before him, entered the field in pursuit of the eugenicist’s dream of enhancing the human stock through the controlled breeding of people. “I had come to Galton’s ideas by my own parallel reasoning spurred by the common youthful wish to improve the world, and by reading Fisher,” Hamilton wrote shortly before his death in 2000. “I much liked the notion that human-directed selection, whether to maintain standards or to speed the intellectual and physical progress of humanity, could be made more effective and more merciful than the obviously inefficient and cruel natural process.” Although this dream sustained his early studies of altruistic behavior, Hamilton’s later work on another major evolutionary puzzle left unsolved by Fisher—the so-called problem of sex—dampened his enthusiasm for state-controlled eugenics and deepened his appreciation for the efficiency of natural selection.

Sexual (as opposed to asexual) reproduction comes at a huge biologic cost to the individual. The birthing female transmits only half of her individual or genetic identity to her offspring. The payoff comes in variation as the genetic material from two parents passes on in new combinations. Under evolutionary models that rely exclusively on individual or gene-level selection (rather than group selection or intelligent design), synthetic theorists began questioning whether the payoff justified the cost. Among biologists taking up this puzzle, who included such leading neo-Darwinists as George C. Williams and John Maynard Smith, Hamilton offered perhaps the most convincing (though far from universally accepted) reason why sexual reproduction predominates among species that produce few offspring. He called it the “parasite Red Queen hypothesis”—in reference to the character in Through the Looking-Glass who had to run as fast as she could just to stay in place—a name borrowed from biologist Leigh Van Valen’s more general “Red Queen” hypothesis of an evolutionary arms race. It relied on the premise that sexual reproduction produces more genetic variation than asexual reproduction. Hamilton proposed that slow-reproducing organisms need the added variation coming from sexual reproduction to stay ahead of their rapidly reproducing asexual parasites. “The hosts’ best defense may be based on genotypic diversity, which, if recombined each generation, can present to the parasites what amounts to a continually moving target,” he explained in a coauthored 1988 article.

The parasite Red Queen hypothesis, with its emphasis on random genotypic diversity, convinced Hamilton that any controlled scheme of eugenic breeding would fail through a lack of genetic variation. Better let natural selection take its course, he concluded, whatever the pain. Yet his youthful enthusiasm for planned reproduction merely gave way to later-life concerns about the dysgenic effects of advances in health care that allow people (such as diabetics, he noted) to survive and reproduce their deleterious genes. “I predict that in two generations the danger being done to the human genome by the ante- and postnatal life-saving efforts of modern medicine will be obvious to all,” he warned in a posthumously published autobiographical account. Hamilton simply could not stop worrying about humanity’s future: Perhaps it was in his genes.

Just as Gould joined in leading the scientific opposition to sociobiology, he loudly protested any return to eugenic thinking. Gould saw the two as inexorably linked in a damnable hereditarian view of humanity. During the 1980s, he wrote popular books and articles exposing “the mismeasure of man” that bedeviled earlier efforts to devise eugenic standards for human reproduction. Hamilton attributed Gould’s position to a Marxist’s misguided commitment to human equality, while Ruse viewed it as at least partially rooted in a Jew’s memory of the Holocaust. Indeed, Gould did not limit his assault to sociobiology and eugenics but took on fundamental tenets of the modern synthesis that supported them. In doing so, he offered an alternative scientific view of how evolution operates that challenged genetic reductionism.

Gould complained that exclusive reliance on the natural selection of genes to account for evolution ignored factors that shape organisms. With Richard Lewontin in 1979, Gould argued that developmental constraints limit and channel adaptations. Certain features (such as the Tyrannosaurus’s reduced front legs) may serve no adaptive purpose, they suggested, but instead arise as a by-product of other adaptions (such as larger hind legs). Over the years, Gould expounded the view that form does not inexorably follow function and that much is left to chance in the lottery of life. “If a large extraterrestrial object—the ultimate random bolt from the blue—had not triggered the extinction of dinosaurs 65 million years ago, mammals would still be small creatures, confined to nooks and crannies of a dinosaur’s world, and incapable of evolving the larger size that brains big enough for self-consciousness require,” he commented in 1996. Gould’s view flew in the face of the progressivism implicit in much modern neo-Darwinian thinking. Given the enormous adaptive advantage of intelligence and cooperation, for example, both Hamilton and Wilson believed that the evolution of self-conscious, altruistic beings was far from accidental. Their depictions of kin-based and reciprocal altruism in various types of social animals supported their faith in evolutionary progress. “Since natural selection has invented both kinds of altruism numerous times,” the like-minded science writer Robert Wright explained, “it is not too wild to suggest that this expansive sentiment was probable all along.”

Beginning in the 1970s, Gould worked with American Museum of Natural History paleontologist Niles Eldredge in formulating the theory of punctuated equilibria to account for the pattern of organic life preserved in sedimentary rock. “The oldest truth of paleontology proclaimed that the vast majority of species appear fully formed in the fossil record and do not change substantially during the long period of their later existence,” Gould noted in an obvious reference to Cuvier’s findings. “In other words, geologically abrupt appearance followed by subsequent stability.” The modern synthesis, in contrast, presented evolution proceeding gradually, by minute adaptations, without sharp divisions of individuals into enduring species. For generations, Darwinists confidently predicted that further research would smooth out the fossil record into the predicted pattern of gradual change, but it never happened. Increasingly, synthetic theorists extrapolated from their mathematical models and population studies to chart the course of evolution, while relegating fossils to museum exhibits calculated to impress upon the public that evolution happens. Gould and Eldredge resisted this role for their field. Instead, they took its findings seriously and tried to explain them in evolutionary terms. To do so, they drew on Sewall Wright’s classic (but unfashionable) notion of nonadaptive genetic drift as developed in Ernst Mayr’s so-called “founder principle” of allopatric speciation.

Mayr had proposed that new species form when a small population becomes geographically isolated from the main group—such as a few mainland finches blown to the Galápagos Islands. The new or particularized environment, coupled with a greatly restricted gene pool, accelerates the evolutionary process and facilitates the formation of new species, Mayr suggested. Once established, though, the new species should become as stable as the old one. This process, Eldredge and Gould observed, should generate the pattern they found in the fossil record: long periods of equilibrium or stasis in species, punctuated with the abrupt appearance of new ones. “If new species arise very rapidly in small, peripherally isolated local populations, then the great expectation of insensibly graded fossil sequences is a chimera,” they wrote in 1972. “A new species does not arise from the slow transformation of all its forebears. Many breaks in the fossil record are real.”

By the time Eldredge and Gould proposed their theory, however, Mayr’s founder principle played little part in mainstream evolutionary thought, which Eldredge characterized as having become ultra-Darwinian. “Ultra-Darwinians are really followers of Ronald Fisher,” he asserted, “seeking to explain all evolutionary phenomena strictly in terms of natural selection acting on heritable variation within populations.” Synthetic theorists came to view the founder principle, like Wright’s concept of genetic drift, as insignificant in its evolutionary effect as compared with gene-based adaptations in large populations—such as the selection of black peppered moths in a darkened environment. Now Eldredge and Gould sought to revive it as a primary explanation for the patterns preserved in the fossil record and, in doing so, to give special significance to speciation within the overall evolutionary process. “Species represent a level of permanence that acts to conserve adaptive change far beyond the ephemeral capacities of local populations,” Eldredge asserted. Drifting further from the neo-Darwinian mainstream, Gould later proposed that nonadaptive developmental constraints and macromutations might also impact evolution, at least at higher levels of the process. There is something real about species, he stressed, that resists change without a jolt beyond that required for lower-level variation among individuals and within populations. Using language certain to inflame synthetic theorists who believed that evolution operated the same way at all levels, Gould differentiated between “microevolution” within species and “macroevolution” of higher-level taxa.

Gould’s ability to communicate his heresies to an educated audience through best-selling books and popular articles fed the public perception of a revolution within evolutionary thought, when in reality the rebellion was limited largely to one wing of paleontology. Even Gould soon retreated from his grander claims. For his part, Eldredge maintained that the “abrupt appearance” of any new species under the punctuated-equilibrium model would still take generations of gradual change—he estimated “from five to fifty thousand years”—and did not involve macromutations. Any plausible version of punctuated equilibria, Mayr insisted, is compatible with the modern synthesis. Nevertheless, purporting to speak for mainline neo-Darwinists generally, Maynard Smith dismissed Gould’s view of evolution as “so confused as to be hardly worth bothering with.” Robert Wright added, “He stresses its flukier aspects—freak environmental catastrophes and the like—and downplays natural selection’s power to design complex life forms. In fact, if you really pay attention to what he is saying, and accept it, you might start to wonder how evolution could have created anything as intricate as a human being.” Gould’s view thus contrasted sharply with that of Hamilton, Wilson, and other ultra-Darwinists who saw the creation of humans as all but inevitable in the naturalistic processes envisioned by the modern synthesis. Wright dismissively dubbed Gould as “the accidental creationist,” even though Gould steadfastly proclaimed his commitment to evolutionary materialism.

Despite challenges, the naturalistic modern synthesis stands at the heart of current evolutionary science. Genetic mutations and recombinations, this view maintains, cause organisms to vary. The fittest of these various individuals survive to pass along their genes. Change builds gradually, without discrete breaks. As synthetic botanists have asserted all along, hybrid crosses between nearly related species add to the gene flows that cause individuals to vary. Recent research suggests that (much as happens in genetic engineering) viruses and bacteria can invade the cells of other organisms and implant their own genes or genes from other organisms into the host’s DNA. Again, variation can result. Natural hybridization and gene acquisition join mutation and recombination as the genetic fodder for natural selection to sift and winnow in evolving the diversity of life.

Nearly 150 years of research in biology since Darwin’s publication of Origin of Species have enriched the evolutionary account of organic origins that Wilson now calls “epic.” The evolutionary epic began with the appearance of self-replicating cells on Earth some four billion years ago, scientists estimate. Multicellular life came more than three billion years later; hominids stood erect on the plains of Africa beginning about five million years ago; and the first of our species walked into history within the past hundred thousand years. “There is a grandeur in this view of life,” Darwin wrote in the last sentence of The Origin of Species, “that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” With this, all manner of modern evolutionists would agree. Even if they cannot wholly accept Wilson’s depiction of “a cause-and-effect continuum from physics to the social sciences, from this world to all other worlds in the visible universe, and backward through time to the beginning of the universe,” they share the awe implicit in a well-known movie title that Gould adapted in naming his most popular book. Accident or not, it is a wonderful life.


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