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Since favorable mutations are served up so slowly, major evolutionary change will ordinarily require vast expanses of time. There are, as it turns out, ages available. Processes that are impossible in a hundred generations may be inevitable in a hundred million. “The mind cannot grasp the full meaning of the term of a million or a hundred million years,” Darwin wrote in 1844, “and cannot consequently add up and perceive the full effects of small successive variations accumulated during almost infinitely many generations.”12
The time scale problem was formidable when Darwin wrote. Lord Kelvin, the greatest physicist of the late Victorian age, authoritatively announced that the Sun—and therefore life on Earth—could be no more than about a hundred million (later downgraded to thirty million) years old. The fact that he provided a quantitative argument, plus his enormous prestige, intimidated many geologists and biologists, Darwin included. Is it more probable, Kelvin asked,13 that straightforward physics was in error, or that Darwin was wrong? There was in fact no error in Kelvin’s physics, but his starting assumptions were mistaken. He had assumed that the Sun shines because of meteorites and other debris falling into it. There was not the faintest hint in the physics of Kelvin’s time of thermonuclear reactions; even the existence of the atomic nucleus was unknown. As late as the first decade of the twentieth century it was believed that the Earth was only 100 million years old, instead of 4.5 billion, and that the mammals had supplanted the dinosaurs only 3 million years ago, instead of 65 million.
On the basis of these misconceptions, Darwin’s critics argued—properly—that even if evolution worked in principle, there might not be enough time for it to do its stuff in practice.* On an Earth created less than ten thousand years ago, it was absurd to imagine that species flowed one into another, that the slow accumulation of mutations could explain the varied forms of life on Earth. It made sense, not merely as an expression of faith, but as legitimate science, to conclude that each species must have been separately created by the same Maker who had only a moment before created the Universe.
The breakup of rocks by the waves, the transport of rock powder by the winds, lava flowing down the sides of a volcano—if the Earth is only a few thousand years old, such processes cannot have much reworked the face of our planet. But the most casual look at the landforms of Earth reveals a profound reworking. So if you imagined from biblical chronology that the world was formed around the year 4000 B.C., it made sense to be a catastrophist—and believe that immense cataclysms, unknown in our time, have occurred in earlier history. The Noachic flood, as we’ve mentioned, was a popular example. If, though, the Earth is 4.5 billion years old, the cumulative impact of small, nearly imperceptible changes over the course of ages could wholly alter our planet’s surface.
Once the time scale for the terrestrial drama had been extended to billions of years, much that had once seemed impossible could now be readily explained as the concatenation of apparently inconsequential events—the footfalls of mites, the settling of dust, the splatter of raindrops. If, in a year, wind and water rub a tenth of a millimeter off the top of a mountain, then the highest mountain on Earth can be flattened in ten million years. Catastrophism gave way to uniformitarianism, championed by Lyell in geology and by Darwin in biology. The accumulation of vast numbers of random mutations was now inevitable, unavoidable. Great cataclysms were discredited and special creation became, both in geology and biology, a redundant and unnecessary hypothesis.
Many advocates of uniformitarianism denied that quick and violent biological change had ever occurred. T. H. Huxley, for example, wrote, “There has been no grand catastrophe—no destroyer has swept away the forms of life of one period, and replaced them by a totally new creation: but one species has vanished and another has taken its place; creatures of one type of structure have diminished, those of another have increased, as time has passed on.”14 In the light of modern evidence, he was right in general, right for most of the history of the Earth. But he went too far; clearly it is possible to acknowledge the importance of slow, cumulative, background change without denying the possibility of occasional global cataclysms.
In recent years it has become increasingly evident that catastrophes have swept over the Earth, generating vast alterations both in land-forms and in life. Major worldwide discontinuities in the record in the rocks are readily explained by such catastrophes; and abrupt transitions in the forms of life on Earth, occurring in the same epoch, are naturally understood as mass extinctions, times of great dyings. (Of these, the late Permian is the most extreme example, and the late Cretaceous—when the dinosaurs were all snuffed out—the best-known). Previous ecologies are then supplanted wholesale by new teams of organisms. The fossil record shows that long periods of very slow evolutionary change are often interrupted by rarer, episodic intervals of quick change, the “punctuated equilibrium” of Niles Eldredge and Stephen J. Gould.15 We live on a planet in which both catastrophes and uniform change have played their roles. In the purported distinction between all-at-once and slow-and-steady, as in much else, the truth embraces seemingly antithetical extremes.
The case for special creation has not been strengthened by this new balance. Catastrophism is an awkward business for biblical literalists: It suggests imperfections in either the design or the execution of the Divine Plan. Mass extinctions permit the survivors to evolve quickly, occupying ecological niches formerly closed to them by the competition. The painstaking selection of mutations continues, catastrophes or no catastrophes. But the wiping out of whole species, genera, families and orders of life, the randomness of mutation, the infelicities in the molecular machinery of life, and the slow evolutionary fiddling displayed in the fossil record—of trilobites, say, or crocodiles—all reveal a tentativeness, a hesitancy, an indecision that hardly seems consistent with the modus operandi of an omnipotent, omniscient, “hands-on” Creator.
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Why are many cave fish, moles, and other animals that live in perpetual darkness blind, or nearly so? At first the question seems ill-conceived, since no adaptive reward would attend the evolution of eyes in the dark. But some of these animals do have eyes, only they’re beneath the skin and don’t work. Others have no eyes at all, although anatomically it’s clear that their ancestors did. The answer seems to be that they all evolved from sighted creatures that entered a new and promising habitat—a cave, say, lacking competitors and predators. There, over many generations, no penalty is paid for the loss of eyesight. So what if you’re blind, as long as you live in pitch darkness? Mutations for blindness, which must be occurring all the time (there being many possible malfunctions in the genetic instructions for vision—in eye, retina, optic nerve, and brain), are not selected against. A one-eyed man has no advantage in the kingdom of darkness.
Similarly, whales have small, internal, and wholly useless pelvises and leg bones, and snakes have four vestigial internal feet. (In the mambas of Southern Africa a single claw from each rudimentary limb breaks through the scaly skin to plain view.) If you swim or slither and never walk anymore, mutations for the withering away of feet do you no harm. They are not selected against. They might even be selected for (feet can be in the way when you’re pouring down a narrow hole). Or if you’re a bird that finds itself on an island devoid of predators, no penalty is levied for the steady atrophy, generation after generation, of wings (until European sailors arrive and club you all to death).