Enigmas of Evolution

by Jerry Adler and John Carey

n 1902, 70 million years after it tripped lightly through the Mesozoic forests in search of meat, the skeleton of a 20-foot-high tyrannosaurus was dynamited out of a sandstone bluff near Hell Creek, Mont. Wrapped in burlap and plaster and shipped back to New York, the bones were painstakingly reassembled by fossil curator Barnum Brown of the American Museum of Natural History. It was there, one day in 1947, that they happened to scare the bejesus out of 5-year-old Stephen Jay Gould. With a mouthful of teeth as big as bananas, the great reptile gaped down at the little mammal who had usurped its place at the head of the food chain and set him scurrying for the safety of his daddy's pant leg. It was a sublime epiphany. Long after Gould could stare with equanimity at the skull of tyrannosaurus, he was left with the essential mystery that still motivates him as perhaps America's foremost writer and thinker on evolution: why should dinosaurs have ended up in human museums instead of—as one among an infinite number of evolutionary possibilities—the other way around?

One morning not long ago, Gould was on his hands and knees in a grove of casuarina pine trees on the Bahamian island of Eleuthera. He was pursuing his fieldwork on Cerion, a genus of land snail that grows to the unimpressive length, compared to dinosaurs, of 4 centimeters. At noon he stood, dusted off his blue trousers and headed for the airport to catch a plane to New York, where he was to receive the National Book Critics Circle Award the next day for his book on intelligence testing, "The Mismeasure of Man." He picked up the award and immediately returned to the Bahamas. This was in January, a month in which Gould delivered three papers at the annual meeting in Washington of the American Association for the Advancement of Science; flew to Chicago to discuss his MacArthur Foundation grant ($38,400 a year for five years); dispatched an essay to The New York Times about the Arkansas creationism trial (for which he was star witness for the plaintiffs); wrote a magazine article on evolution, plus his regular monthly column in Natural History magazine, and gave the last few lectures in his enormously popular course at Harvard ambitiously titled, "History of Earth and Life."

In one sense Gould is just another enlisted man of science, pushing back by a few inches the frontiers of man's knowledge of snails; but he is also a general who has helped transform the entire landscape of evolutionary theory. His chief weapon is his uncanny knack for communicating ideas simply, elegantly and persuasively. His Natural History column gives him a power over popular opinion exceeded only by those scientific immortals who have their own series on public television.

His ability to communicate across specialties makes him a rare drawing card at professional conferences. Physicists and astronomers who wouldn't cross the street to look at a duck-billed hadrosaurus packed the AAAS seminar to hear Gould's paper on "Hardening of the Evolutionary Synthesis"—and then walked out en masse on the next speaker, the great biologist Ernst Mayr. "He is a phenomenal individual," says Tom Schopf of the University of Chicago, one of Gould's leading scientific adversaries. "He begins lectures quoting from the King James Version and ends them singing Gilbert and Sullivan." Such brilliance is not always welcomed in a serious scientist; there is still a prejudice that ideas must compete in the marketplace unadorned and naked, like chickens. But even Schopf admits: "If he didn't have something sensible to say, people wouldn't listen to him."

In 1972 Gould and Niles Eldredge—a paleontologist at the American Museum of Natural History—collaborated on a paper intended at the time merely to resolve a professional embarrassment for paleontologists: their inability to find the fossils of transitional forms between species, the so-called "missing links." Darwin, and most of those who followed him, believed that the work of evolution was slow, gradual and continuous and that a complete lineage of ancestors, shading imperceptibly one into the next, could in theory be reconstructed for all living animals. In practice, Darwin conceded, the fossil record was much too spotty to demonstrate those gradual changes, though he was confident that they would eventually turn up.

But a century of digging since then has only made their absence more glaring. Paleontologists have devoted whole careers to looking for examples of gradual transitions over time, and with a few exceptions they have failed. It was Eldredge and Gould's notion to call off the search and accept the evidence of the fossil record on its own terms. Rather than transforming gradually, most of the species in the world appear to have evolved relatively quickly (on the scale of geologic time) and to have persisted, virtually unchanged, for millions of years.

That seemingly innocent proposition was the wedge that helped break open the ruling scientific consensus about evolution. If Eldredge and Gould's theory of "punctuated equilibrium" is correct, we are forced to revise our views about natural selection, the keystone of Darwin's thinking. Evolution, in the orthodox Darwinian view, is driven by the relentless competition among individuals for limited resources and mates. Giraffes are the winners of a long race to the top of the acacia tree; human beings are the survivors in a rigorous contest, renewed each generation, to outsmart their fellow sapiens. It is the awesome responsibility of every creature to advance the cause of his kind. Every advantage must be conserved to pass on to the next generation; natural selection is an invisible monster perched outside each nest and burrow, ruthlessly exterminating those who fall behind.

But here was a way to lift some of the burden of natural selection from individuals. Members of the same species appear to compete within a range of values fixed when the species originated; their life-and-death struggle takes on less significance, because it produces very little evolutionary change. Instead, by mechanisms not yet understood, new species appear to split off at random from existing ones. If they have some advantage, they may in time supplant their ancestors, although it is also possible that both species will coexist for a long time—until, as usually happens, a major change in the environment wipes out one or both of them.

The rule applies to Homo sapiens as it does to other species. Steven M. Stanley, a Johns Hopkins paleontologist who has been a leading contributor to the new theory, presents evidence in a recent book [The New Evolutionary Timetable. By Steven M. Stanley. 222 pages. Basic Books. $16.75.] to show that human beings did not evolve by the gradual growth of the brain from one generation to the next but discontinuously, with the replacement of small-brained species by larger-brained ones (diagram, page 46). By implication, the basis for social Darwinism is undercut: human progress is not inevitably fueled by relentless mano a mano competition for the choicest nesting spots or the biggest offices. Moreover, we can no longer view ourselves as the perfect result of a process of testing and refinement going back 3 million years to Australopithecus. We are merely the latest, and perhaps not the last, of a series of hominid species.

Like evolution itself, the progress of science is not always smooth, frustrating historians who try to fill in the gaps between papers. Shortly after the 1972 paper, Gould had an inkling of some of its broader implications and resolved to think them out. As a result of an accident on a Harvard squash court, he found himself in bed for five days with both eyes bandaged and put his formidable mind to the problem. "I didn't get a single good idea," he says ruefully. "I listened to a lot of basketball games." Five years went by before he and Eldredge wrote on the subject again. Both men agree that Eldredge had the original insight into punctuated equilibrium and that Gould was more creative in working out the significance of it. But that distinction is lost on the public. Eldredge, who also advised the anti-creationist side in the Arkansas trial although he didn't testify, recalls a meeting where "a lawyer was telling me about Gould's theory of evolution. I wanted to punch him in the face."

For all the excitement it has generated, punctuated equilibrium still smacks of heresy to many scientists. It does not explain what many regard as the crucial point: how and why a new species springs up. Evolutionary biology is an uneasy synthesis of paleontology, population genetics and comparative anatomy, each with its own point of view and priorities. Population geneticists have worked for decades among their fruit-fly bottles to explain evolution by the gradual spread of genetic change among individuals, and they can't believe that a totally new mechanism is responsible for all the truly important evolutionary events. There is a vast conceptual gap between the two disciplines as well. As a paleontologist, Gould deals casually in eons and epochs; when he asserts that species arise "relatively quickly," he means in relation to the rate at which fossils accumulate, in which 50,000 years is little more than an instant. To geneticists, for whom the crucial unit of time is the ten-day reproductive cycle of the fruit fly, that's just the kind of attitude they'd expect from a pick-and-hammer scientist.

These disagreements were thrashed out in healthy debate, stopping just short of character assassination, at the notorious Chicago conference on evolution in 1980. Gould—sarcasticlly dubbed "The Prince of Evolution" by one speaker—was at center of the controversy. "They said things about me that they wouldn't say about anyone else," he recalls mildly. But, like a battling couple that doesn't want to wake the baby, the scientists paused between blows to see if any creationists were listening. Their worst fear is that creationists, who have fought Darwin for so long, will seize on any criticism of him as vindication for their own faith. Nothing could be more mistaken, says Gould. "Evolution is a fact, like apples falling out of trees. Darwin proposed a theory, natural selection, to explain that fact. Newton's theory of gravitation was eventually superseded by general relativity. But apples didn't stop in midair while physicists debated the question."

It is an embarrassment to Gould when he occasionally finds himself enlisted, without his consent, in the creationist attack on evolution. In fact, his Natural History column has been one of the more imaginative and effective defenders of evolutionary enlightenment. The unsophisticated defense rests on the perfection of nature: the polar bear so ingeniously, invisibly white; the great veldt-colored cat streaking across the plain in streamlined pursuit of dinner. But Gould considers that a weak argument; creationists could just as easily—and do—argue that these perfect adaptations are the product of an omniscient Creator. Gould's subtler defense rests on the odd detours and dead ends of evolution, which testify to the hit-and-miss processes of the natural world.

Consider, he urged in one famous essay, the panda's thumb. It is an appendage beautifully suited to the panda's sole occupation, which is peeling the leaves off tasty bamboo shoots, but it is not a digit at all. The evolutionary pathway leading to opposable thumbs, which simians embarked on millions of years before there were baseballs to throw with them, was not taken by the panda's ancestors. Like all bears, the panda has five forward-pointing fingers suitable for running and stabbing; its "thumb" is improbably constructed out of a greatly enlarged wristbone, the radial seesamoid (page 48). It is an inelegant solution, whose only virtue is that it works. Surely, Gould argues, if God had made the panda, he would have done a neater job.

Gould is a great believer in putting scientific ideas into their cultural and political context. Darwin, he has written, was probably drawn to a gradualist view of evolution by the slow pace of change in nineteenth-century England. Punctuated equilibrium, on the other hand, would seem to have attractions to the modern mind, particularly one schooled in dialectics. It is not surprising, Gould and Eldredge wrote in 1977, that Soviet paleontologists embrace a version of the theory. "It may also not be irrelevant," they went on, "that one of us, learned his Marxism, literally at his daddy's knee." ("I said I learned it," Gould is reported to have added once; "I never said I believed it.")

Gould grew up in New York City, where his father dreamed his revolutionary dreams while pursuing a hobby as a naturalist and a humdrum career as a court stenographer in Queens County Supreme Court. The narrow escape from tyrannosaurus awakened the first stirrings of intellectual curiosity in Gould, something his parents may later have considered a mixed blessing as he dragged them each summer through abandoned quarries and dry riverbeds, searching for dinosaur bones. He never found any, although he filled five boxes full of little marine brachiopods and trilobites. Years later—after Antioch College and a brilliant graduate career, nominally at Columbia but actually at the American Museum of Natural History—he had the honor, as curator of invertebrate fossils at Harvard's august Museum of Comparative Zoology, of merging his collection with Harvard's.

Gould now works happily, amid the accumulated detritus of 4 billion years of natural history, at a cluttered desk in one corner of a vast storeroom filled with dusty specimen cabinets: "Triassic," "Ordovician," "Silurian." His armchair is surely no older than Devonian times. As brash as he is scientifically, his social profile is virtually horizontal. He considers the worst possible taste when he discovers that a scientific colleague carries a business card. "Ten years ago that would have been unthinkable," he grumbles. "It's an aspect of the conservatization of America." He uses his full name professionally, except in the left-wing journal Science for the People, where his by-line is contracted to the minimally pretentious "Steve Gould."

His brontosauran appetite for work is the envy and despair of his colleagues. "He calls me at 11 at night Massachusetts time," says his frequent collaborator David S. Woodruff, a biologist at the University of California at San Diego, "and we talk until 11 my time. Steve starts getting creative at midnight, works until 2 or 3, then gets up at 6:30." For relaxation from his disciplined, organized professional life, he lets himself go by singing baritone in the Boston Cecilia Society, a highly regarded amateur chorus. What time is left is jealously guarded for his family. He is close to his widowed mother, who runs a shop on Cape Cod where she sells driftwood sculptures of owls and a small stock of books, the collected works of Stephen Jay Gould. He has attempted to shield his wife, Deborah, and their two sons from the growing publicity attached to his name. A passage in his most recent book revealed that his older son, Jesse, 12, suffers from a learning disability. A friend speaks with awe of Gould spending several hours each night patiently reading and talking to his son, never despairing that he could overcome this problem, like he has so many others, by sheer will and effort.

Although he never surrendered his first love, the dinosaur, Gould eventually came to the realization that it was a poor organism on which to base a study of evolution; the specimens are too few, too large to fit in the lab and they can't be bred. He has embraced instead the land snail, a far more practical animal, and one that is not without interest in its own right. Gould is most interested in the genus Cerion, which since its first description by Linnaeus in the eighteenth century has been divided into 600 different species, based on a baffling diversity of size, shape, color and shell texture. The divisions were made by nineteenth-century naturalists who cruised among the Bahamas as the guests of rich yachtsmen and collected snails at each beach; if they had troubled to walk between the beaches, as Gould has done, they would have found the hybrid zones that link many of the seemingly separate colonies. What appeared to be separate species are in fact no more different than Eskimos and Tatars. About twice every year for the past decade, Gould and Woodruff have visited the islands, and are well along in, the task of reclassifying Cerion into fewer than twenty legitimate species, demolishing along the way 2,000 pages of taxonomy.

As fieldwork goes, it is relatively undemanding, even without a yacht. A yard a week is a good pace for a cerion, so there is no question of having to chase them down, much to the relief of Woodruff, whose graduate work was on a rare nocturnal frog of the Australian swamps. For part of their expedition last January, the two scientists were accompanied by Gould's younger son, Ethan, 8.

He scrambles ahead of them, plucking cerions from among the sea grapes and lilies while pursuing his own lines of inquiry: Does the snail like it in the plastic bag? Does it matter if I get some snail BM on my fingers? When do we eat lunch?

Gould and Woodruff are more interested in identifying the boundary between two neighboring species: the cylindrical, brown-striped C. glans, and the conical, all-white C. agassizi (by coincidence named after Alexander Agassiz, whose father, Louis, was the great naturalist who founded the Harvard museum where Gould works). They investigate the west side of a large brackish pond, but the two colonies don't seem to meet there, so they work their way down a narrow neck of land between the pond's eastern edge and the sea. Jouncing slowly along a 5-foot-wide path in their 6-foot-wide Chevrolet, they stop every few yards for a sample. Agassizi, agassizi, agassizi. Something a little bit less clearly agassizi. Now, a definite glans influence. In these quiet woods, something significant is happening: either two different populations are mingling at their boundaries or one ancestral species is differentiating into two. Suddenly, very close to clear glans territory, Gould picks up an almost perfect agassizi. "This is technically known as an anomaly," Woodruff explains. "In an earlier age, it would have been dealt with by tossing it as far into the woods as possible." The disposition of anomalies is the source of much scientific humor. In this rigorous age, the woods are not an option open to Gould and Woodruff.

Gould picks up a specimen from the hybrid zone. "See that purple on the top of the shell?" he muses. "You see that sometimes after an injury. It makes sense if you think of hybridization as a form of injury . . . it discombobulates the developmental system." At the end of the day, Gould is well satisfied. "We made a major discovery today. There's no way it will interest more than eight people in the world, but those eight people really care."

Woodruff gets first crack at the collected snails, since he needs them alive to map their genetic composition. He then ships the empty shells to Gould, who measures—or rather, has his graduate students measure—twenty separate physical variables on each (they have studied more than 10,000 so far). The only other person who has found a use for empty cerion shells is Gould's mother, who discovered that they make nice beaks for her owl sculptures. Gould's work is aimed at isolating, from the welter of varying shapes and sizes, a few basic mathematical principles which underlie the construction of all of them. One reason for suspecting that such principles exist is that Woodruff has shown that no matter how different their shells look, the genetic make-up of cerions varies little. So perhaps just a few master, or "regulatory," genes controlling the rate of growth are responsible for generating the different shells.

Biologists believe this is a common phenomenon. Humans and chimpanzees, for example, are remarkably similar in their genetic compositions—so much so that Gould believes it might be possible for the two species to hybridize in what he calls "the most potentially interesting and ethically unacceptable experiment I can imagine." It also appears that human anatomy is closer to that of young apes than adult apes; the infants, for example, have relatively larger craniums. To turn a chimpanzee into a person, a small number of genetic changes, slowing down the rate of development to retain some juvenile features, may be all that's needed.

The correlation between the growth of various parts of an animal—the field known as allometry—has long been one of Gould's main interests. Snails are excellent animals on which to study allometry, since they preserve a record of growth from birth. But they lack drama—compared, say, to the Irish elk, a fossil deer that stood higher than a man and swung 90-pound antlers that were 11 feet across, a formidable organ of dominance. For one of his more memorable essays, Gould set out to measure the skeleton of every Irish elk he could find in the museums of two continents and discovered that allometric principles operated even on such grand excrescences: a simple formula related the size of the antlers to the size of the deer that bore them.

Gould considers this one of the most important and powerful of evolutionary principles, because it frees scientists from the need to explain all the parts of an animal in terms of their evolutionary usefulness. If the growth of different parts is linked, then much of what we see in an organism may be just an accidental consequence of something else more important. The principle is as obvious as your big toe, which appears to have developed as it did for no better reason than to keep up with your thumb. "Repeated parts of the body are not fashioned by the action of individual genes," Gould has written; "there is no gene 'for' your thumb, another for your big toe … Repeated parts are coordinated in development … It may be genetically more complex to enlarge a thumb and not to modify a big toe, than to increase both together."

This runs counter to the powerful tradition of adaptation in evolutionary thought: the tendency to atomize organisms into separate traits, each with its own history and justification. One can, in an example of what Gould calls "vulgar Darwinism," look at the relative hairlessness of Homo sapiens as an adaptation to running around on the hot African savanna and then assert that eyebrows evolved to keep dandruff out of the eyes and pubic hair to trap the odors of sexual attraction; or one can look at the set of features as the retention of a basically embryonic pattern—a chance consequence of the general slowdown in development that made apes into humans. Applying the strict adaptationist argument to hair is merely a waste of time, Gould believes; attempting to make it fit the subtleties of human behavior is downright dangerous. He has been a leader in the attack on sociobiology, the theory that human behavior can be analyzed as separate traits—as broad as aggression, as elusive as creativity, as uncommon as homosexuality—each with its own genetic basis and its own evolutionary justification. Gould considers this notion both an absurd reductionism and an invitation to biological wool-gathering of the most useless sort, such as the speculation that a gene for music was bred into the human race because it was so useful in the rituals that kept tribes together. To Gould this is just an advanced form of phrenology. A brain is an integrated whole, a network of correspondences far more subtle and interesting than those that link the thumb and the big toe; whatever specific advantage the brain may have held 50,000 years ago, it can be put to far higher use today.

The attacks on sociobiology and its founder, Harvard's Edward O. Wilson, were among the bitterest intellectual fights of the 1970s, and it is not a period Gould likes to dwell upon. It was, like the current struggle against the creationists, partly a political fight; apart from its scientific content, Gould saw sociobiology—with its implication that human potential is largely determined by genes—as a threat to the liberal proposition that the environment is more important. His most recent book, "The Mismeasure of Man," is a detailed history of the scientific attempts to rank people by intelligence, all of which, he says, failed as science and most of which curiously arrived at the conclusion that the topmost rung was occupied by white males of the scientist's own nationality. The book contains an entertaining evocation of an earlier age in which skulls were measured by filling them with mustard seeds, but it is permeated by Gould's implicit assumption that dwelling on the differences between people is an essentially mischievous exercise.

Gould, in fact, extends the hand of brotherhood even to other species. If rank prejudice supported nineteenth-century scientific racism, prejudice of a subtler sort led twentieth-century paleontologists to conclude that dinosaurs were dumb beasts marked for certain extinction. Gould's willingness to see another point of view has led him to imagine himself back in the Cretaceous era, in the skin of a tyrannosaurus. "Looking at the little mammals crawling around down there," he muses, "would I see anything inevitable about their rise? I think not." If Darwin dealt a blow to the notion that man was created by divine edict, Gould has gone further and upset the marginally comforting image of evolution as a gradual climb up the slope of perfection, at whose crest stands man. We have, instead, a kind of sideways dance in which the last few steps, luckily for us, have been in our direction. We have no way of knowing where it's headed next; all we can say for sure is that it will go on.

[ Jerry Adler, John Carey, "Enigmas of Evolution," Newsweek March 29, 1982, pp. 44-49. ]

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