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Breaking Tradition With Darwin
By JAMES GLEICK

http://www.nytimes.com/images/e.gifVOLUTION has prepared the Bahamas land snail for a simple life. It hangs upside down from the leaves and grasses, climbs down in the damp nights to nibble at fungi and crawls across the terrain at the sober rate of perhaps a meter per year. Over the ages, merely by struggling to survive and reproduce, it has managed to adapt itself exquisitely to its various Caribbean habitats. On the coasts, where wind and crabs might kill the less fit, natural selection has left snails with thickened shells for protection. In the sun-dappled interiors, shells have grown mottled for camouflage.

But no means of adaptation known to Darwin could have prepared these snails for a predator as ruthless as a certain Harvard professor of geology. When January comes, the scattered islands of the Caribbean find him scrabbling at the ground with his fingernails, a plastic bag dangling from his mouth, barely aware of the clouds of sand flies or the 90-degree heat. He carries away specimens by the hundreds and maps their geographic distribution. It is his way of staying in touch with the stuff of evolution.

To a scientist like Stephen Jay Gould - an evolutionary theorist with a special love for patterns of growth and form - these snails make perfect subjects. For one thing, their life histories are calcified for all to see in the delicate whorls of their shells. For another, they turn up in a wild variety of shapes - so wild that species-happy collectors a century ago gave names to what they thought were more than 600 different kinds (Gould thinks there are fewer than 20).

A traditional Darwinian would ask how these many snails adapted to their local habitats over the course of millenniums. What are all those different shapes for? Gould is asking a different question, and it amounts to a kind of heresy in the already conten- tious world of evolutionary theory. He wants to know whether all those different shapes, all those elegant histories of growth, might have little at all to do with adaptation. Like some other evolutionists in the United States and Britain, he is challenging some of the most basic tenets of how species originate and change. And he is proposing a broadened theory, giving greater roles to the laws of internal development, the necessities of organic architecture and the vagaries of chance.

''There's more diversity of form within this single genus of Bahamian land snail, Cerion, than within any other family of land snails,'' Gould says. ''You get these pencil-thin snails. You get these golfball-like snails. A colleague of mine once gave as an example of an impossible animal a square snail, and I pointed out to him that there's a square Cerion. Everything happens with Cerion.''

Gould used to see the snail hunting as a sideline, to be indulged the way an architect might enjoy an occasional bout of carpentry. ''If you just did theory all the time you'd feel like a whore, trading on ideas and not building up the data of the field.'' But this summer, after interminable hours at Harvard spent staring at his pages of data, he also realized that the fieldwork had something to contribute to his grander theories. More orthodox evolutionists would assume that the many changes of form represent adaptations. Gould denies it and finds explanations in the laws of growth. Snails grow the way they do because there are only so many ways a snail can grow.

There is a paradox here, and Gould and his colleagues are all aware of it. Publicly, Gould is the foremost exponent of Darwinism in our time. His monthly column in Natural History magazine over the last decade, collected in three engaging and successful books, has explained the wonders of evolution to an increasingly devoted corps of readers. His prolific writing and his teaching - barely slowed by a painful struggle during the last year against a deadly form of cancer - have made him a popular focus for honorary degrees and other awards, including a five-year John D. and Catherine T. MacArthur Foundation prize fellowship.

One collection of essays, ''The Panda's Thumb,'' won the 1981 American Book Award, and his study of human intelligence and biological determinism, ''The Mismeasure of Man,'' won the National Book Critics Circle Award last year. His undergraduate course, Harvard's basic course on ''The History of the Earth and of Life,'' drew more than twice as many students this fall as could be accommodated. His outspoken campaign against the creationist notion of species placed here by divine and immutable design may not have converted many fundamentalists, but it gave the lay public the most forceful defense of evolution to come from the scientific community.

Yet within the field, this 42- year-old paleontologist is putting himself more and more at odds with orthodox Darwinism - the body of evolutionary thought grandly known as the ''modern synthesis.'' He accuses it of hardening of the arteries. In a major address before the American Academy of Arts and Sciences in October, as in several recent scholarly papers, he has taken a stand against some of the basic principles of the modern synthesis - primarily the idea that the great trends of evolution can be explained purely in terms of Darwin's ''war of nature,'' the struggle of individual organisms to survive and reproduce.

The struggle of the evolutionists has already begun to bear heavily on the questions that have always made this such a contentious subject: Where did we come from and where are we headed? Darwin stands with Freud and Marx as one of the modern era's great bearers of bad tidings precisely because his revolution overthrew so many cherished answers to such questions. Those who wished to see humanity as the appointed captain of a divinely arranged parade of life got no comfort from biology after Darwin's time.

Yet the vision he put in its place was in its own way a vision of harmony, of order, of progress. Are we not evolving, slowly but steadily, toward some smarter, healthier, longer-lived race of the future? Of all the images of evolution that have taken hold in Western culture in the century since Darwin, this one is the most basic, and it may simply be wrong. For Homo sapiens, Gould and some of his colleagues believe, biological evolution is already over.

''We're not just evolving slowly,'' Gould says, ''for all practical purposes we're not evolving. There's no reason to think we're going to get bigger brains or smaller toes or whatever - we are what we are.''

His challenge reflects a lively turbulence in the field, and more turbulence is sure to come over the next few years as discoveries from molecular biology flood into evolutionary theory. Gould himself is molding the pieces of the debate into a unified, hierarchical view of evolution that he believes will give scientists a framework for talking about the interplay of great events at the levels of species, populations, individuals and genes.

''We need a different structure of evolutionary theory,'' he declared, ''an expanded kind of Darwinism but one that looks very different from the reductionistic version that has been our orthodox theory for the last 40 years or so.'' It is a new chapter being written by Gould and other biologists in the modern history of evolution - what is, after all, our story of genesis.

''Steve has been the major intellectual input into the debates in evolutionary biology,'' said John Maynard Smith, professor of biology at the University of Sussex, England, and himself one of the great theoreticians of Neo-Darwinism. ''I say that even though I think he's often quite wrong-headed, and I'm sure he thinks the same of me. But his is the intellect that stimulated this whole thing.''

As the debates go on, the heart of Darwin's message will surely remain intact. Individuals within a species vary. Those best fitted to their environment survive to pass their favorable traits on to their descendants. Nature's selection of the fittest acts as the engine of change over the generations.

But if Gould prevails it will no longer be quite as easy to explain every character, every trait, every bit of behavior in terms of how it helps an organism survive or reproduce. That has become a common habit of thinking not just in evolution but also in fields like anthropology. Why do mammals have four legs? Because it's the most efficient number for walking. Why do people have chins? To facilitate speech, or eating. Why do some cultures practice human sacrifice? To compensate for shortages of protein.

Here are the nonadaptationist explanations: We have four limbs because we evolved from fishes with four fins - ''we had to make do with that,'' Gould says, ''and we've done a good job.'' Chins don't even exist, morphologically speaking - they are just an accidental result of the interplay between two growth fields in the receding jaw of Homo sapiens (the tooth part receded more than the lower part). And human sacrifice could have arisen for any number of cultural reasons, but the use occasionally made of the resulting flesh was an afterthought.

Gould and some of his colleagues call the adaptationist habit Panglossian, as in Voltaire's joke: Why do people have noses? To hold up spectacles.

To many practicing evolutionists, this view is a caricature and a straw man. They have a staggering fact of nature on their side: that so many animals and plants do seem superbly adapted to their habitats. That, after all, is what Darwin set out to explain.

Still, Gould's heresies have been productive before. A decade ago, he and Niles Eldredge, a fellow paleontologist at the American Museum of Natural History in New York, broke with orthodox Darwinism by proposing a new model for the pace of evolutionary change. The traditional view was, and is, that big changes are made gradually, by the accumulation of many tiny changes over eons. Gould and Eldredge, joined now by many other American and British paleontologists, argue for a theory of fits and starts. Most important change, they believe, takes place in the geological instant when a new species is born - a long instant, to be sure, lasting perhaps 5,000 to 50,000 years, but virtually no time at all compared to the millions of years most species survive. After that first burst of change comes a long period of stability.

The fits-and-starts theory - known as punctuated equilibrium, or, familiarly, as ''punk eke'' - addresses one of the great nuisances of evolutionary theory, the fossil record. As creationists love to point out, the evidence preserved in the earth's rocks shows many species virtually unchanged throughout their histories, with precious few transitional stages between them. Darwin and his successors have had to argue that the fossil record is incomplete by its very nature, preserving only a tiny fraction of organisms and preserving them at unreliable intervals. Gould and Eldredge ask whether the rocks might not after all be telling a true story. Perhaps transitional stages rarely appear because their existence really was brief.

This initial break with Neo- Darwinism, now accepted by many in the field, gave the modern debates their shape, but its implications have remained poorly understood except by specialists.

One piece of evolutionary theory that has firmly established itself in the way we think about human origins is the idea that we descended from our primate ancestors by continuously improving features such as brain size. Gould and Eldredge challenge that, suggesting that the important history of human ancestors is not a matter of gradual improvement, but of new humanlike species splitting off from the old. Our evolutionary history is more like a copiously branching bush than a ladder toward perfection. The new species probably formed quickly in small, geographically isolated populations and from then on, Gould and Eldredge argue, they remained more or less static. ''So that at any one time,'' Eldredge suggests, ''you might have two or three species of various brain sizes, and the long-term winners of their competition would be the bigger-brained species. It's an analogue of natural selection at the species level.''

A major area of contention to flow from punctuated equilibrium is just this suggestion - that individuals are not the only players on the evolutionary stage. Perhaps species or local populations or even genes can be targets of natural selection. That is the basis of the hierarchical model of evolution that Gould and others are building - a model meant to explain the great events, the birth and death of species and the reshaping of ecosystems.

Whether natural selection is sorting individuals or species, it is still a process of adaptation - and the traditional view remains that what we are, what we have made ourselves, arises from usefulness in survival and reproduction. Gould challenges that as well.

''I don't doubt for a moment that there was a conventional selective reason for our large brain,'' he said. ''That reason's probably complex - there are a whole host of interrelated advantages of large brains. What I do want to say very strongly is that most of what our brains do - most of what is essential to our considering of ourselves as being human - is not directly selected for, is not a product of natural selection, but arises as a nonadaptive structural consequence of building a computer so powerful as the human brain.

''To give just one example: The most terrible fact that the evolution of the large brain allowed us to learn is the fact of our personal mortality. Think of how much of the architecture of human culture and cultural traditions, how much of human religion, for example, arises and attempts to deal with that terrible fact, which we have come to learn as a result of the complex structure of our brain. You can't argue the brain became large so that we would learn the fact of our coming personal mortality.''

Even Gould's allies sometimes part company with him on the question of adaptation. ''He's trying to redress the balance, as he sees it,'' Eldredge says. ''The modern synthesis has tended to throw out the caveats and just take natural selection and extrapolate the whole thing up the board and explain the whole history of life with it. He's quite right to point that out, but I think he's infatuated with the notion. There is tremendous design in nature, and species are adapted to an amazing extent.''
Gould tends to look instead to organisms that adaptation seems to have left behind, organisms that seem imperfect or jerry-built. Where orthodox Darwinism stresses the movement of evolution toward perfection, toward harmony, his view leaves more to the accidental and the unforeseeable. ''It does emphasize the quirkiness, the unpredictability of evolution,'' he said. ''I've never seen that as a negative or despairing message. I know some people don't like it. To me it only teaches that you won't passively read the answer to moral questions in nature. And that just throws the challenge out to humanists: It's up to us to struggle and find that meaning ourselves.

''That's no threat,'' he added. ''To me that's a promise and a challenge more than a counsel of despair.''

A minor dogma of evolutionary theory, firmly held by geneticists and paleontologists around the country, is that Steven Jay Gould sleeps only three hours a night. ''Look, no normal person doing a normal day's work could possible accomplish what he's accomplished,'' said Sherwood L. Washburn, professor emeritus of anthropology at the University of California at Berkeley, an evolutionist who has often differed from Gould.

Actually, Gould says, with the help of the Winston Churchill catnap technique, he used to manage on four or five hours. But that was before he discovered he had cancer.

He canceled last winter's trip to the Bahamas but kept writing his monthly column and teaching his Harvard classes, wearing a hat, by the end, to cover the baldness that came with intense radiation treatment and chemotherapy. ''It speaks to an inner strength that is intimidating,'' says David S. Woodruff, an ecologist and geneticist at the University of California at San Diego and Gould's longtime partner in the Bahamas fieldwork. ''The man has such incredible self- drive, motivation and control.''

Woodruff gets the snails first, to study 20 to 30 different genes in each, and then he ships the shells east to Harvard. Gould makes a set of complicated measurements and writes the numbers in rows and columns on immense pads. Then he searches for patterns in the measurements. It was one kind of work the cancer made impossible for a while.
But Gould's schedule is already nearly back to its precancer level. His major work in progress, already known to most of his colleagues as his ''macroevolution book,'' will detail his expanded version of evolutionary theory. He is writing a series of five technical papers on the snails and planning a Caribbean trip with Woodruff in January. He sings in the Boston Cecilia Society and often joins the substantial corps of Yankee rooters at Fenway Park. He also spends a great deal of time with his family: his wife, Deborah, an illustrator; his 14-year-old son, Jesse, who suffers from a learning disability, and his 10-year-old son, Ethan.

Gould was born on Sept. 10, 1941, in Manhattan and grew up in Forest Hills, Queens. The legend - and he swears it is true - is that he determined to become a paleontologist at the age of 5, when his father, a court stenographer, took him to see Tyrannosaurus Rex at the American Museum of Natural History. He never wavered, attending Jamaica High School in Queens - just before Sputnik brought a flurry of science courses into the curriculum - Antioch College in Ohio and graduate school at Columbia University. He joined the Harvard faculty in 1967.

Besides his undergraduate lecture course, he teaches a small seminar with his graduate students - often beginning the class with a ritual reading of his hate mail. He gets plenty, because of the active part he took in the creationism debate, writing articles and testifying in a well-publicized trial in Arkansas. ''There was one particularly nasty one from a woman who identified herself as a nurse, a preserver of life, you see. She said I was going to die - which I'm not, damn it, I'm going to be a survivor - and that I was sure to burn in hell.''

Gould discovered his cancer by accident, and the accident saved his life. He went for a physical examination in July 1982 before a trip to Europe. ''It's one of those funny things - I still don't know to this day why I asked him to do it - but I realized as I was about to leave that he hadn't given me a prostate exam, and I remembered that my old doctor used to. So I asked him, 'Well, what about a prostate exam.'
''He said, 'I don't usually give them to men your age because prostatic cancer is essentially unknown in men in their early 40's, but since you ask I'll give it to you.' So he did and he found this little bump - it's not prostatic cancer because indeed that is unknown in men my age.''

It was mesothelioma - the asbestos-related cancer that forms either in the lung or the abdomen. Gould can think of no exposure to asbestos, but it can take extraordinarily little. If the discovery had come a few months later, he might have had no chance. ''The problem is,'' he said, ''the general statistics on mesothelioma - you don't even want to read them.''

He read them. He went straight to the library at Harvard Medical School, punched mesothelioma into the computer and got the latest literature. Then he decided the statistics did not apply to him. Most victims were older. Most lived farther from a major medical center. Most only discovered the cancer after it produced noticeable symptoms. ''That's what's rare, to discover it in its presymptomatic state. It's the only reason I had a chance at all.''

Gould and I sat alone in his office at Harvard's Museum of Comparative Zoology. It is a cavernous room in the museum's original wing, built in 1859, the year Darwin published ''The Origin of Species.'' Gould shares it with 20,000 trilobites in glass cases and with an extraordinary personal book collection, including rare tracts on evolution from before Darwin's time. Not long ago, painters uncovered lettering on the old walls - ''Synthesis of the Animal Kingdom,'' ''Sponges and Protozoa'' - and Gould realized that the room had once been a main exhibition area of the museum. He left the lettering exposed.

While I sat at a table covered with snails and microscopes, Gould finished some yogurt and rose from a rattan chair. In his own mind, he sometimes says, he is a fat man. He used to be, but these days, of course, the reality is that he is just small, wearing his new gauntness like a battered overcoat. When he speaks, his energy seems to channel itself in his eyes and in his enormous hands - he flares them, locks them, kneads them as he paces back and forth. But in the afternoons he often gives way to his fatigue, and this was one of those times. He began sorting slides for his lecture that evening. ''It's funny,'' he said. ''You can't really predict how you're going to react to something like that until it happens. I never would have known what my reaction would be to, you know, a threat on one's life of that magnitude and sort. I might have thought that I would get very scared and very angry, but I just didn't. And I gather that's not an uncommon reaction among cancer patients - when you're threatened you just sort of reach back and you say, 'Oh, well, there it is, what am I going to do.' You deal with it.''

Doctors could reach one tumor surgically the month it was detected. Another could not be touched until it had been shrunk by radiation. ''It turned out that it was one of these - you see, the problem with mesothelioma is that it - .'' He held a slide up to the gray light of the window, and dropped it into a box. ''It never forms a single solid tumor, it unfortunately always forms the tumor and then undergoes this local spreading where you get these little dots of disease all over the - .'' Another slide. ''It tends not to metastasize distantly, and that's the one, if you will, somewhat favorable feature, that it does not have this tendency to spread throughout the body. But because it forms all these dotlike spreads, it's essentially uncurable under older techniques. There was not a whole hell of a lot you could do.''

Gould underwent surgery again last December and began an experimental form of chemotherapy. High doses of chemicals were applied directly on the cancer through a tube in his abdomen. It was successful, but infection from the tube caused peritonitis last spring, and the peritonitis nearly killed him.

''I can't complain,'' he said. ''It's true that everything was going along so well, and then to be struck with these two crosses, first one of your kids turns out to have deep problems, and then to come down with this life-threatening condition in your early 40's - .Well. Everything else had gone so well.

''The further difficulty that I live with is the knowledge that the mesothelioma statistics are pretty daunting. But look - I'm an individual. That's the essence of taxonomic biology, after all: the irreducibility of the individual. The general statistics may not mean a lot.

''The important thing is just to keep active. The main way to fight it is to just keep telling yourself you're not going to let it stop you. Then if it gets you eventually, O,K, you lose. But I'm not going to let it stop me.''

Even now, as the day wears on, the pain sometimes gets to be too much, and Gould goes off to give himself an injection of a narcotic painkiller.

When Gould ran his evolutionary challenge up the flagpole of the American Academy of Arts and Sciences, one of the chief architects of the modern synthesis, Ernst Mayr, was sitting in the front row, furiously scribbling notes. Mayr, a longtime Harvard professor and author of ''The Growth of Biological Thought,'' rose afterward to offer a quick response and elaborated on it the next day.

''It's a brilliant tour de force that Steve has produced,'' he said. ''Presumably I am to defend the old antiquated ideas of evolution, and let me just say it wouldn't be too difficult for me to do that.'' Like many evolutionists, he rejected the notion that natural selection operates on species or populations or genes. And he doubted that constraints of development or architecture could be as useful as adaptation in studying the Bahamas land snail. ''That's where we are on thin ice,'' Mayr said, ''and there is no thinner ice than Steve's ice.''

Mayr and other traditional Neo-Darwinists often suggest, quite reasonably, that Gould is recycling old ideas. They also argue that he is exaggerating their importance. John Maynard Smith, for example, does not think punctuated equilibrium will prove quite as pervasive as Gould thinks. ''And I don't think we were as na'ively gradualist as you would think to hear Steve talk about it.''

He also notes that as long ago as the 1950's he was talking about some of the issues Gould now stresses - but he agrees that just about any idea in evolutionary theory can be traced back to the literature not just of the last generation but of the last century. It's a question of emphasis. When he claimed priority for one idea at a recent conference, a colleague interrupted and said, ''Yes, John, we all know you invented the bloody bicycle, but you didn't get on and ride it anywhere.''

''We get this in science all the time,'' Mayr said, ''that the first glimmer of a new idea turns up very early in the literature, and gradually it becomes brighter and brighter until finally somebody makes a term for it, or somebody makes a big noise about it, and finally it penetrates people's awareness.'' As sharply as he disagrees with Gould's expanded theory, he expects it to be a force to reckon with, particularly when the macroevolution book is finished. ''It's going to be taken seriously and it's going to have a tremendously stimulating influence on the field.''

When Mayr and other Neo- Darwinists resolved the early struggles of evolutionary theory by blending the discoveries of Mendelian genetics, they settled firmly on one of the many conceivable agents of change: natural selection. Scientists by then had no use for mystical notions of change directed from within, and the new understanding of genetics ruled out the idea, known as Lamarckism, that traits acquired by an individual could be passed on. A weight-lifter's children just don't start life with bigger muscles, as nice as that might be for the progress of evolution.
Natural selection not only seemed to work, it also - just as important - provided a program for doing science.

''For the first time,'' as Gould says, ''what Darwin says is that what you can study are these small-scale changes occurring within populations - artificial selection and breeding of sheep and plants and pigeons, small changes that you can observe in the timescale of a generation. That these are the stuff, through extrapolation, of all evolutionary change.''

This was the happy state of scientific life that Gould and Eldredge began to disrupt a decade ago by suggesting that those tiny, slow changes may not account for the major events of evolution - that gradualism has become a bad habit.

Gould loves to display examples from modern anthropology: drawings of progressively more human-looking creatures walking in line, getting less and less stoop-shouldered as the eons wear on - even though the supposedly intermediate stages walked perfectly upright, according to pelvic reconstructions. He also points to the so-called McGregor busts, which used to be a favorite of college anthropology departments.

''He's given us a supposed gradual transformational sequence of Homo erectus,'' Gould said, ''a Java man on the left, to Neanderthal in the center, to Cro-Magnon on the right. The problem is that it's not an evolutionary sequence.

''Neanderthal is not an intermediate form - it's us. It's a Western European race of Homo sapiens, presumably. But look what McGregor has done to reinforce that impression of intermediacy - he's given Neanderthal a three-day growth.''

Punctuated equilibrium changes everything. Instead of looking at the daily war of individuals to survive, evolutionists have to shift their focus upward to the levels of populations and individuals, just as molecular biology is looking downward to discover important patterns at the level of genes. Gould believes that the next great conceptual gains will come from the study of how these levels interact. There, he argues, lie explanations for long-term trends that have mystified paleontologists and for many other pieces of the evolutionary puzzle.

One such piece - the kind of natural oddity that fills Gould's columns and makes his books so much fun to read - is what biologists call overspecialization. In the animal world, overspecialization leads to features like the peacock's tail or the huge antlers of the Irish elk. ''The organism is doing what it ought to do as a Darwinian agent,'' Gould said, ''trying to win more copulations to pass on more of its genes to future generations. It does that by developing a highly precise specialized organ which limits the flexibility of the species with respect to future evolutionary change, eventually guaranteeing the extinction of the species.'' Good for the individual, bad for the species. In the orthodox view, that is a contradiction in terms, awkward to deal with. In the hierarchical view, it is a kind of negative feedback between levels.
As the picture broadens, as evolution becomes a history of abrupt change when new species are born and when old ones die, it may be that the important trends will owe more to the necessities of architecture, as in Bahamian land snails, or in developmental constraints that will only be understood when embryology explains more of how genes control the timing and direction of growth. Gould's major scholarly work, the 1977 ''Ontogeny and Phylogeny,'' was devoted to the importance of viewing evolution as a change not in final products but in histories of development. ''If there are only a few potential pathways of evolutionary change,'' Gould says, ''if those potential pathways are set by the structure of the organism, then, even if natural selection is doing the pushing, in a sense the organism pushes back. Its inherited structure exerts very strong constraints on the possible pathways of change.''

Even when natural selection is the driving force, it may not be as universally effective as orthodox Darwinists suppose. Some traits may hitchhike on the backs of others. For example, in a cataclysmic event like the great extinction of 60 million years ago, when dinosaurs gave way for good, the explanation for the triumph of mammals may lie not in their bigger brains, but in the good fortune of their small size. It was the big creatures that died, regardless of how smart they were. The little creatures survived, and their brains came along for the ride.

Darwin encouraged the notion of human evolution as a march toward perfection in passages like the famous peroration to ''The Origin of Species,'' from which Gould drew the title of his Natural History column, ''This View of Life.'' It's a picture with a sense of purpose: ''As natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress toward perfection. . . . Thus, from the war of nature, from famine and death, the most exalted object of which we are capable of conceiving, namely the production of the higher animals, directly follows. There is grandeur in this view of life.''

There is indeed. But Gould loves to show a picture of a little fish, complete with eye, fins and tail, that turns out to be the rear end of a clam. The clam has evolved a highly specialized decoy. ''In what sense can you say this is a 'better' clam?'' he asks. ''Is it better than an oyster? Is it better than a scallop?'' It's just one adaptation among millions to particular ways of living.

The history of life is full of creatures that became more and more complex, only to shed their complexity when a changing environment demanded simplicity. Some ecological niches favor organisms that live long lives, producing few offspring but devoting great energy to their protection and development. Others favor organisms that rely on sheer reproductive force, maturing as quickly as possible, breeding by the thousands and then dying. Which approach is ''better''? It depends on the environment.

For one organism alone, the environment has become a thing to shape, rather than a thing to be shaped by. And in some small ways, our interference with our environment has already had the power to affect our own genetic legacy. Medical science, by curing some diseases, can allow unfavorable traits to remain in the gene pool, an effect known as dysgenic. But genes are complicated. They rarely restrict their effects to one particular disease, and they almost never correspond in any neat way to the parts of the finished animal. As for less visible and more interesting traits, if an object as simple as the chin has no clear genetic existence, there is no reason to think qualities like intelligence are directly coded either.

A few diseases seem to have simple genetic triggers, but even the simplest cases can have unexpected consequences. No genetic disease is better understood than sickle-cell anemia, a blood disorder affecting blacks.In its rare, homozygous form, it is deadly. But the mild, heterozygous form, much more common, has a beneficial side effect: It provides protection against malaria. That is why the gene spread in Africa, wherever the malaria was present. Natural selection favored it, as long as it stayed rare enough so that few people would be unlucky enough in the genetic draw to get the deadly form. By tampering with nature and wiping out the malaria, science has not weakened our genetic stock - on the contrary, it has accidently strengthened the selection pressure that is now eliminating sickle-cell anemia.

For humanity, biological evolution is reserved for such oddities. The message of punctuated equilibrium is that only cultural evolution matters now. ''Think of Cro- Magnon people 50,000 years ago,'' Gould said. ''They were us. There's no difference in the brain capacity and intellectual abilities. What's happened is all cultural evolution.''

Cultural evolution is powerful and fast because, unlike the biological kind, it is truly Lamarckian. What is acquired in one generation can be passed on to the next. Its engine of change is learning. Its genetic code is language. In the century since Darwin, many students of social trends have tried to find parallels in natural selection, and some have succeeded. But because it is Lamarckian, cultural evolution does not need to wait for the slow and savage weeding out of the unfit.

In the meantime, where could biological evolution take us? Even given hundreds of millions of years, there is no reason to think nature would craft eyes that could see molecules, legs that could carry us hundreds of feet per second, brains that could sort or calculate as rapidly as computers. Even in matters of sickness and health, the time is long past when our bodies' best hope lay in evolution. Until recently, none of nature's creations could guess the future or change it - yet suddenly there is, as Gould says, one interesting and imperfect exception.