RONALD CLARK has had the bright idea of treating Charles Darwin as if the great naturalist (and his natural selection theory) were themselves engaged in the great "struggle for existence" which he identified in 1859 as the shaper of life forms.

It is a brilliant literary conceit, offering Clark a handy framework for a fascinating study in intellectual history -- not merely the genesis of Darwinism but the challenges set in its way from Darwin's day to our own.

If you're one of the millions who've imagined that Darwinism, because problematical and still disputed, has been on that account invalidated, this is probably your book.

Clark ultimately concludes that Darwin and his theory have indeed survived, despite hazards that might have relegated a shakier, less useful theory to the scientific dustbin. Such loss or overthrow occurs often enough in the history of science. When Darwinism was young, struggling for a foothold in mid-Victorian times, it was believed that the propagation of light required a medium, the so-called "ether." The ether, thanks to the relativity revolution, is no more. Darwinism, in transmogrified form to be sure, stands.

So many obstacles lay before Darwin that near misses constitute a fascinating aspect of the story. Among the many what-ifs: What if Darwin had not been sickened by medical studies, and had not become a naturalist? What if he had, as once intended, become a country clergyman, whose surmises about the natural order had for that reason scandalized the age even more than they did? What if he had not signed on as the naturalist of HMS Beagle, the oceanographic surveying ship; or if the Beagle had not visited the Galapagos Islands? What if the distinguished ornithologist John Gould had not called Darwin's attention, soon after his return from the five- year voyage, to the curiosities of the mockingbirds and finches he'd brought back? That there were three species of the former, and 13 of the latter? What if, somewhat later, the sudden appearance of Alfred Wallace's competing evolutionary theory had not spurred the dawdling Darwin to commit The Origin of Species to print? What if the reviewer for The Times had been one of the many hostile ones, not "Darwin's bulldog," Thomas Henry Huxley? What if Darwin's always touchy health had broken down?

To be sure, Darwin might have vaulted all these hurdles. Nonetheless, all things considered, Darwin's success and "survival" illustrates the chanciness of scientific history -- at least as much as the 40-year obscurity into which Mendel's contemporaneous genetic experiments fell.

And of course, as arwin himself explicitly recognized, he had challenged the cosmology of his age quite as severely as Copernicus had the age for which the sun moved about the earth.

Even with the resurgence in the past 20 years of "creationism" as an allegedly "scientific" rival of evolution, it is hard for us to grasp the sense of shock that swept the Victorian world. Darwin's theory seemed, first, to link man by implication to "lower" life forms; and, secondly, to supplant the age-old belief in a special, purposive creation with the chilling view that all species gradually arose by a blind, groping process of competition, struggle and adaptation.

There were some who sought, immediately, to soften the blow by attempting to reconcile evolution with divine design. But of one of these efforts, Darwin observed that "the author makes God a great breeder of animals who selects & works like an improver of short horns or a pigeon fancier." As Clark shows, it is mistaken to think that scientists rallied to the theory while churchmen scorned and denounced it; there were praise and objection on both sides, though it would be some time before intellectual respectability shifted in its favor and the better lights of the church, such as Bishop Gore, sought to demonstrate that God and natural selection need not be enemies. "At Oxford," Clark tells us, when the great spat over The Origin of Species raged, "Obadiah Westwood, professor of zoology, seriously proposed . . . the establishment of a permanent lectureship for the exposure of the fallacies of Darwinism." Even Darwin, for that matter, had come slowly and reluctantly to his painful parting with "special creation" as then understood. Once persuaded, however, he never looked back; and it was a mark of the splendid English catholicity and tolerance, more than exact understanding of his views, that permitted his burial in Westminster Abbey (near Newton) in 1882.

A more serious and enduring threat to Darwin's survival than the fulminations of the clergy were certain enduring puzzles. There was chiefly the utter incompleteness of the fossil record, for instance. The theory of natural selection called for thousands of "intermediate" life forms never yet discovered. The resulting awkwardness was partly of Darwin's making, an uncharacteristic dogmatism. He had been warned by Huxley from the start not to rule out the possibility that nature moved by jumps. But Darwin clung to the view that species developed by a steady, excruciating gradualism, step by stately step, with adaptations rewarding even the most minute modifications. This classic form of Darwinism, now refined into "neo-Darwinism," has held great sway in this century, especially in the statistical study of populations. It is now, however, under serious challenge from the theory of so-called "punctuated equilibrium," postulated by Stephen Jay Gould and others. Under the latter theory, species are presumed to enjoy long periods of morphological stability, "punctuated" with sudden, swift modifications. It has been gaining adherents; and a recent study showing a swift transformation of Gal,apagos finches (of all creatures) under drought conditions seems to buttress it.

FINALLY, Darwinism was long haunted, as was Darwin himself, by another great mystery: Assuming that forms demonstrably evolved, then stabilized into new species, what was the mechanism? There was much groping in blind alleys until, in succession, the rediscovery of Mendel, the genetic experiments of Thomas Hunt Morgan, and the breaking of the DNA code finally unveiled the secrets of hereditary transmission.

However formidably challenged, Darwin survived; and that for good reasons. He was the most careful, patient and assiduous of observers. The poor man, exclaimed his gardener, might "moon" over a mere flower for minutes at a time. His kindness and intellectual honesty were legendary. He strove to anticipate difficulties and objections and face them candidly. When puzzled he admitted it, as in his famous remark that the complexity of the human eye made him "shudder." He had, said his son Francis years later, "the power of never letting exceptions pass unnoticed."

Today, the overwhelming majority of biologists argue over how, not whether, evolutionary variation occurs. And while the recent trend seems to have set in against "neo-Darwinism" and indeed to some degree against "natural selection" itself as the sovereign mechanism of change, there is no serious question of Darwin's permanence. Darwinism, a powerful, comprehensive and adaptable theory, has met the test of survival of the fittest.

Clark's is a fascinating, if at times formidably technical, study of one of the great episodes in the history of science, ancient or modern, covering the whole story from the incubation of Darwin's earliest doubts about the permanence of specieto the latest quarrels over taxonomy. The Survival of Charles Darwin is, in short, an important contribution to the understanding of a much misunderstood subject, and deserves a survival of its own.