Darwin’s conclusion was that natural selection leads to the origin of new species. Because the world is constantly in a state of change, nature favors the varied—a community of predominantly white moths is better off if it contains a few dark moths, against a smoggy day—and the geographically dispersed, those who do not keep all their eggs in one basket. As a result, the degree of individual variations found within a given species tends to increase with the passage of time, until some groups have become so different from others that they can no longer mate and produce fertile offspring. At that point, a new species has emerged. As Darwin wrote:
During the modification of the descendants of any one species, and during the incessant struggle of all species to increase in numbers, the more diversified the descendants become, the better will be their chance of success in the battle for life. Thus the small differences distinguishing varieties of the same species, steadily tend to increase, till they equal the greater differences between species …16
Darwin noted that in some ways his theory recalled the biblical image of the Tree of Life. But now the tree, instead of being static as in the creationist view, had come alive and was still growing:
The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species…. The Tree of Life … fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.17
Critics with a preference for Bible stories complained that natural selection was cold and mechanical. But in Darwin’s eyes it both animated and illuminated the natural world:
When we no longer look at an organic being as a savage looks at a ship, as something wholly beyond his comprehension; when we regard every production of nature as one which has had a long history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the possessor, in the same way as any great mechanical invention is the summing up of the labor, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting—I speak from experience—does the study of natural history become!18
And he added, in what was to become an evolutionists’ credo:
There is a grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and 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.19
Darwin had formulated the essential elements of his theory by the time of his marriage in 1839, and by 1844 had outlined it, in a 230-page essay. Yet he withheld it from publication for the next fifteen years. While the essay lay in his desk drawer, accompanied by strict instructions to publish it in the event of his death, Darwin settled in the country, fathered ten children, corresponded with Lyell and a hundred other scientists, and wrote books—among them a journal of the voyage of the Beagle, an account of his theory of coral reefs, a treatise on volcanos and another on the geology of South America, and a masterful study of barnacles that consumed seven years of work and left him fuming that “I hate a barnacle as no man ever did before.”20 In all, Darwin kept his theory of evolution a secret for nearly as long as Copernicus had concealed his heliocentric cosmology. Why the delay?
One explanation, still sometimes put forward, is that Darwin was constantly ill. This will not wash. Ill he certainly was: From about the time of his marriage and probably long before he was subject to intense headaches, vomiting, and heart palpitations. He consulted the best doctors in England in search of a cure, had himself hypnotized, and resorted to hydrotherapy, spending winter days wrapped in a cold, wet sheet. “His life,” wrote his son Francis Darwin, “was one long struggle against the weariness and strain of sickness.”21 The ailment was never conclusively diagnosed and has since been attributed to many agencies, from Chagas’ disease, brought on by what Darwin called the “attack (for it deserves no better name) of the Benchuca, the great black bug of the pampas” on March 26, 1835, to the psychosomatic affects of internal conflict between this former candidate for the priesthood and the anticlerical implications of his own theory. A more likely if less colorful possibility is that he suffered from severe allergies. But in any case, illness alone cannot explain why Darwin suppressed the theory of natural selection, since during those same years he wrote prolifically on other subjects.
It is much more likely that Darwin feared the storm of opposition he knew his ideas would provoke. He was a gentle, straightforward, almost childishly simple man, habitually respectful of the outlook of others and disinclined toward disputation. His theory, he knew, would draw down fire, not only from the clergy but from many of his fellow scientists as well.
The religious opposition promised to be formidable. Darwin did not have to strain his imagination to foresee what the orthodoxy would make of his assertion that animals and men are kin and that chance mutations drive evolution; to advocate such a thing, he told his friend Joseph Hooker, would be like admitting to a murder. (The murder of Adam, it was to be called.) Nor did he need look beyond England to envision what lay in store for him once word of the theory got out. When William Lawrence, later president of the Royal College of Surgeons, suggested that man evolves through the inheritance of innate rather than acquired traits, the Lord Chancellor declared his book contrary to Scriptures and denied it copyright. The legendary erudition of Benjamin Jowett of Oxford is recalled in a famous Balliol College masque’s quatrain:
First come I; my name is Jowett.
There’s no knowledge but I know it.
I am the master of this college;
What I don’t know isn’t knowledge.
But when Jowett in 1855 published a controversial interpretation of the Epistles of Saint Paul, he was accused of heresy and his salary was frozen. Darwin, puttering happily with wormstones and petunias in gardens that his insight rendered luminescent as Eden, was not eager to see the day when a thousand country parsons would turn his name into a synonym for the antichrist.
The scientific opposition arose in large measure from professional disdain for the very concept of evolution, which had long been an enthusiasm of ecstatics and occultists devoted to seances and tales of fairies flitting across the moors at dawn. To advocate so amateurish a theory was to invite learned ridicule. When in 1844 a theory of evolution was championed in the anonymous and enormously popular Vestiges of the Natural History of Creation, the book was pilloried by such authorities as the Cambridge mineralogist William Whewell (of whom it was said that “science was his forte, omniscience his foible”), the astronomer John Herschel, and the geologist Adam Sedgwick, who devoted eighty-five pages of the Edinburgh Review to its demolition (and who, indeed, was to subject Darwin’s book to comparable scorn once it finally appeared).
Against these forces Darwin, like Copernicus, would have to defend a theory that he knew to be incomplete, for neither he nor anyone else understood the micromechanism of heredity. “The laws governing inheritance,” as Darwin admitted, “are quite unknown.”22 Missing was proof of the existence of the fundamental hereditary unit, the biological quantum—in short, the gene. Without the stability imparted by genes, innovative mutations would be diluted away like drops of blood in the ocean, before they had time to spread to any significant numbers of individuals. In such a situation natural selection might occur, but it could scarcely account for the origin of species.
The first evidence of the existence of genes did not appear until 1866, eight years after Darwin was obliged to publish The Origin of Species, when the Moravian monk Gregor Mendel published the results of his extensive experiments with green peas in the garden of an Augustinian monastery—results that demonstrated the requisite persistence of the quanta of heredity—and Mendel’s findings were in any event universally ignored until attention was calle
d to them in 1900, by which time Darwin was dead. Darwin sought to make up the deficiency by proposing a theory of “pangenesis” to account for the transmission of hereditary traits, but he remained sensitive to his vulnerability on this count. As he once remarked, he appreciated the shortcomings of his theory better than did most of its censurers.
It was, then, a reluctant Darwin who at Lyell’s urging finally began writing an exhaustive account of the origin of species through natural selection. He intended it to be a massive tome, the completion of which could safely be expected to take years; perhaps, like Copernicus, he would not have to live to read the reviews. But then, on June 3, 1858, when he had written only the first few chapters, everything changed. A letter bearing the postmark of the Malay Archipelago arrived at Darwin’s home. It came from the naturalist Alfred Russel Wallace. It contained the draft of an essay by Wallace titled, “On the Tendency of Varieties to Depart Indefinitely from the Original Type.” Wallace asked for Darwin’s reactions to the paper.
Darwin had a reaction, all right, and it was one of horrified astonishment: The theory outlined in the essay was identical to Darwin’s own. “I never saw a more striking coincidence,” he wrote to Lyell that afternoon.23
Wallace, like Darwin, was an indefatigable collector of plants and insects.* He, too, had been impressed by reading Lyell’s book, had long pondered “the question of how changes of species could have been brought about,” and had hit upon the answer after reading Malthus. He was, he recounted, recovering from malaria when “it suddenly flashed upon me that … in every generation the inferior would inevitably be killed off and the superior would remain—that is, the fittest would survive (Wallace’s italics).25 Wallace drafted the theory in three nights and sent it by the next mail to Darwin, who was known in scientific circles to have some sympathy for the hypothesis of evolution.
Darwin’s initial inclination was to take the high road, renouncing his priority and giving all the credit to Wallace. “I should rather burn my whole book, than that he or any other many should think that I had behaved in a paltry spirit,” he told Lyell.26 But Lyell and Hooker prevailed upon Darwin instead to publish a joint announcement of his and Wallace’s conclusions, and then to get to work writing a briefer account of his theory for prompt publication in book form. This he did, rushing to complete what he called an “abstract” of his theory within a year. This was The Origin of Species by Means of Natural Selection.
More than two hundred thousand words in length, the Origin reads less like an abstract than like a steady, not to say relentless, recounting of specifics: The incidence of beetle spoilage in American purple plums; the size of the stem of the Swedish turnip; the exact number of tail feathers sported by the trumpeter pigeon; the tactics employed by male alligators when they fight over female alligators. The book is objective to the point of bloodlessness; here are to be found no ecstatic outbursts comparable to Copernicus’s tributes to the sun, no philosophizing on a level with Newton’s descriptions of the workings of God, none of the fiery contentiousness of Galileo’s dialogues. Instead there is a constant amassing of factual detail, gradual as a silt deposit hardening into sedimentary rock.*
Indeed, the book was so detailed and modest that it struck many readers as self-evident. This was a source of strength, in that nothing so persuades a man to accept a novel idea as the sense that he already knew it to be true. (“How extremely stupid of me not to have thought of that,” said Thomas Huxley, previously an evolutionary skeptic, upon reading the Origin.27) Many scientists and scholars soon came around to Darwin’s point of view—Hooker at once, the botanist Asa Gray soon thereafter, and Lyell, remarkably for a public figure so prominently established as an antievolutionist, only five years later—though more than a few of them would have agreed with Whitehead, who in a conversation in 1944 declared that “Darwin is truly great, but he is the dullest great man I can think of.”29 Darwin replied to contemporary criticism in this vein with his customary restraint:
Some of my critics have said, “Oh, he is a good observer, but he has no power of reasoning.” I do not think that this can be true, for the Origin of Species is one long argument from the beginning to the end, and it has convinced not a few able men. No one could have written it without having some power of reasoning.30
But he conceded that, though the study of living things had never lost its fascination for him, the years of drudgery had taken a toll on his nonscientific interests: Neither music nor literature nor even “fine scenery” held much pleasure for him any longer; he wrote in his Autobiography: “My mind seems to have become a kind of machine for grinding general laws out of large collections of facts.”31
The religious reaction was every bit as vehement as Darwin had feared, but much of it was so florid, compared to Darwin’s quiet reasonableness, that it flowed around the Origin like water around a rock. Bishop Wilberforce of Oxford set the tone for the long burlesque that was to follow. A passionate lecturer, called “Soapy Sam” after his habit of rubbing his hands together as he preached, Wilberforce condemned Darwin’s theory as “a dishonoring view of Nature…. absolutely incompatible with the word of God.” A prisoner of his own passion, he soon overplayed his hand. The scene was a meeting of the British Association for the Advancement of Science, at Oxford on June 30, 1860. Taking part in the discussion was Thomas Huxley, who loved a good argument and styled himself “Darwin’s bulldog” for his tireless sallies against the opponents of evolution. With a sarcastic smile, Wilberforce turned to Huxley and asked “was it through his grandfather or his grandmother that he [Huxley] claimed his descent from a monkey?”32 “The Lord hath delivered him into mine hands,” whispered Huxley to his friend Benjamin Brodie, seated beside him. Then he rose, savoring the moment, and replied:
A man has no reason to be ashamed of having an ape for his grandfather. If there were an ancestor whom I should feel shame in recalling it would rather be a man—a man of restless and versatile intellect—who, not content with success in his own sphere of activity, plunges into scientific questions with which he has no real acquaintance, only to obscure them by an aimless rhetoric, and distract the attention of his hearers from the real point at issue by eloquent digressions and skilled appeals to religious prejudice.33
The audience broke into laughter. In the general excitement that followed, one Lady Bruster fainted and had to be carried from the hall, while Captain Fitz-Roy of the Beagle marched up and down the aisles, holding a Bible aloft and chanting, “The Book, the Book!”34 The drama of Darwinism versus Christian fundamentalism went on to play to packed houses in the Dayton, Tennessee, courthouse where Clarence Darrow defended John Scopes, and road-show productions were still drawing crowds to the so-called “creation science” trials of the 1980s. One such case reached the Supreme Court of the United States, which voted in 1987 that the state of Louisiana did not have the right to require that creationism be taught alongside evolution in the public schools (Chief Justice William Rehnquist dissenting). But science is not rhetoric, and the evolutionary debates, though entertaining, were always more show than substance.
The ascent of Darwin’s theory brought new vitality to the question of the age of the earth. Darwinism was a time bomb: For species to have evolved to their present-day diversity through the slow workings of random mutation and natural selection required that the duration of the past be much longer than the six thousand or so years suggested by the Bible. Darwin grasped this nettle firmly: “He who … does not admit how vast have been the past periods of time may at once close this volume,” he wrote in the Origin.35
But while Darwin’s evolution and Lyell’s geology implied that the earth was old, they did not prove it. That issue was left to the physicists, who approached the question of the age of the earth by way of thermodynamics, the developing science of the transfer of heat. The earth, as coal miners know, is hotter in its depths than at the surface. Therefore it must be radiating heat into space, rather than receiving all its warmth from the sun. (Wer
e it the other way around, the earth’s surface would be hotter than its interior.) If, then, one assumed that the earth began as a molten ball and has been cooling ever since, and if one could determine the rate at which it is cooling, it ought to be possible to calculate its age.
The first significant experiments along these lines had been conducted in the 1770s by Buffon, an early champion of deep time. In a thermally stable basement laboratory, Buffon fashioned little spheres one to five inches in diameter from suitably earthy materials, heated them, determined how long it took them to cool, and extrapolated the results to the much larger sphere of the earth. He made his measurements by sitting in the dark and observing how long it took a white-hot ball to fade to invisibility, or by touching them with his hand until they seemed to have returned to room temperature. The results, though admittedly crude, yielded a geochronology generous by the standards of the day: Buffon calculated that the earth was some 75,000 to 168,000 years old, and he guessed privately that the true figure was probably closer to half a million years. This, however, was still far too little time for Darwinian evolution to have brought life on Earth from a single-celled organism to the present-day world of orchids and adders and chimpanzees. That feat would have required billions of years.
Coming of Age in the Milky Way Page 25