The Reluctant Mr. Darwin

by David Quammen

  Victorian scientists such as Adam Sedgwick, the crusty old Cambridge professor who had taught Darwin field geology before the Beagle voyage, recognized this challenge clearly, and hated The Origin for it. Sedgwick called the book “a dish of rank materialism cleverly cooked and served up.” Richard Owen, who had studied gorilla anatomy in his lab, ridiculed Darwin for suggesting that “man might be a transmuted ape.” St. George Jackson Mivart, a convert to Catholicism and a former student of Huxley’s, became a zealous evolutionist but balked at natural selection and argued trenchantly against it, positing instead some “internal innate force” as the driving cause of evolution. Whatever produced the physical transmutations from one species to another, Mivart added, could never account for the human mind and soul, which existed in a realm untouchable by evolutionary theory. These critics weren’t deluded or paranoid about what was at stake. They may have failed to absorb the details of Darwin’s theory, and caricatured it in print, but they didn’t misconstrue its implications. The denial of humanity’s special status, implicit in the idea of natural selection acting on undirected variations, acutely distressed many of Darwin’s contemporaries—not just religious leaders and scriptural literalists but also some scientific colleagues, such as the botanist Asa Gray at Harvard, the entomologist Thomas Wollaston, and Darwin’s old friend and counselor Charles Lyell. Their distress was well founded. And this was the point, too, over which Emma Darwin quietly suffered forty-five years of philosophical discordance with her adored and adoring husband.

  Scientific insight and religious dogma had never come more directly into conflict. It was a bigger issue than whether humans and monkeys share a common ancestry. It was the issue of whether humans and monkeys, along with lobsters and dandelions and all other living creatures, share an absence of special divine appointment. In plain language: a soul or no soul? An afterlife or not? Are humans spiritually immortal in a way that chickens and cows aren’t, or just another form of temporarily animated meat?

  Today we tend to overlook this horrible challenge implied by Darwin’s idea. Theistic evolution has supposedly made the theory safe for people of all faiths. But the deep materialism of Darwin’s vision couldn’t so easily be overlooked back when natural selection was a shocking novelty. It assaulted sensibilities. It impeded uptake. Most people nowadays aren’t aware that, at the time of Darwin’s death in 1882, and for two generations afterward, his explanatory mechanism was severely doubted, resisted, and then generally rejected, while evolutionists groped for less repellent alternatives.

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  One of the first serious critiques of Darwin’s theory came from William Thomson, the Scottish mathematician and physicist later known as Lord Kelvin. In 1866, Thomson published a short paper based on his calculations of elapsed time since Earth had formed and solidified. Titled “The ‘Doctrine of Uniformity’ in Geology Briefly Refuted,” it was a one-paragraph snort of disdain, playing on the word “Briefly” while asserting that all earthly history was shorter than some persons supposed. Thomson’s primary target was Charles Lyell, whose uniformitarian view of geological processes entailed slow, steady action over huge stretches of time; Darwin’s concept of slow, steady evolution by natural selection came into question secondarily. Thomson assumed that our planet, having originated as a gob of molten material pulled from the Sun, cooled at a determinable rate as it radiated heat into the chill of space. Given the hot core of magma still remaining, he figured that Earth was probably no more than 100 million years old. That left insufficient time, Thomson argued, for Lyell’s pokey gradualism to have accomplished so much geological change. Darwin, whose thinking was grounded in Lyellian geology, felt the pinch too. One hundred million years was far less than the “incomprehensibly vast” amount of time he had posited for natural selection to shape all life as we know it.

  The pinch tightened several years later when Thomson, having reworked his numbers and considered other factors, began revising the estimate downward. Make that 30 million years, he said. Or maybe just 10 million. Was it possible to believe that Earth’s solid crust was as young as Thomson proposed? Not if you hoped to explain the entire pageant of life—from its Pre-Cambrian doldrums, through the Cambrian explosion of new forms, to the Silurian trilobites, the Devonian ammonoids, the rise and fall of dinosaurs, the age of mammals, and the interesting later trajectory of a certain ape lineage—as resulting from small, undirected variations shaped by natural selection. And vice versa: If you accepted Thomson’s clock, you had to reject Darwin’s scenario. In 1868, now pressing his case explicitly against Darwin, Thomson told an audience that the limitation of time, although it didn’t refute transmutation per se, did seem “sufficient to disprove the doctrine that transmutation has taken place through ‘descent with modification by natural selection.’”

  Darwin grumbled to Alfred Wallace about the “odious spectre” of Thomson, and in revising The Origin for its fifth edition he cut “incomprehensibly vast” to merely “vast,” a reluctant fillip of compromise. He also inserted several sentences acknowledging the difficulty of measuring earthly time, and he conceded that “we have no means of determining how long a period it takes to modify a species.” Darwin’s confidence was tested, but not broken. He could make adjustments.

  Another negative commentary came from Fleeming Jenkin, a professor of engineering who would later become a business partner of Thomson. Jenkin’s long review of The Origin, carried by The North British Review in 1867, criticized Darwin for several supposed mistakes of logic and judgment—most notably, one involving inheritance. Jenkin’s assumption, not unusual for his time, was that the mixing of bloodlines in sexual reproduction brings a proportionate mixing of attributes. If a white man mates with a black woman, the children will be mulatto. If a long-necked goose breeds with a short-necked goose, the goslings will be medium-necked. If a white-flowered plant is crossed with a red-flowered variant, their offspring will flower in pink. True? Not necessarily. Nowadays this is known as “blending inheritance,” a spurious simplification of what actually occurs. But blending inheritance was the sensible-sounding premise from which Jenkin argued, and Darwin had no better theory of inheritance with which to answer him.

  Such blending, Jenkin tried to show, was fatal to Darwin’s theory. Granted, small beneficial variations might increase the reproductive success of some individuals. But in the process of interbreeding, Jenkin thought, those variations won’t be passed along intact. They’ll be diluted by half in each new generation (assuming that only one parent carries the novel trait), and therefore eventually blended away to nothingness. “Fleeming Jenkin has given me much trouble,” Darwin confided to Hooker, around the time he finished work on that fifth edition. He had anticipated the blending inheritance problem himself, as far back as 1838, in his transmutation notebook “C,” when he ruminated vaguely about “the tendency to revert to parent forms.” Now Darwin dealt with Jenkin’s objection, as best he could, by emphasizing a distinction between single variations that appear rarely in a population and variations that appear in numerous individuals simultaneously. The latter sort, allowing a reasonable possibility for two variant individuals to breed with each other, wouldn’t so easily be blended away.

  It was an emergency hedge, and not very persuasive. There was a much better answer to Jenkin’s criticism, but that would become available only later, with the rediscovery of work by Gregor Mendel.

  The unkindest cut against natural selection was delivered by Alfred Wallace, of all people, more than a decade after their joint publication. By then Wallace had been home from the East for seven years and written a magnificent book of travel reportage and natural history, The Malay Archipelago (published in 1869). He had also solidified his friendship with Darwin. He never became one of Darwin’s close confidants, like Hooker or Fox, but he was a very special colleague: the co-discoverer and co-defender of the notorious theory. Apart from Darwin himself, no one understood natural selection better or applied it more forcefully than Wallac
e. His zealotry, in fact, sometimes surpassed even Darwin’s. Wallace saw natural selection operating in certain cases—the gaudy plumage of male pheasants, for instance—where Darwin favored a different causal mechanism. (Darwin’s alternative was sexual selection, the idea that runaway preferences by the opposite sex, not imperatives of survival, are what drive such gratuitously elaborate modifications.) Despite his strong intellectual commitment to the theory, Wallace evidently felt no urgency about asserting his own claim of authorship. He barely mentioned natural selection in The Malay Archipelago, and then with modesty approaching coyness, as an idea “elaborated by Mr. Darwin in his celebrated Origin of Species.” A year later, he reprinted his Linnean Society paper, as well as the “law” paper of 1855 and several others, in a volume he called Contributions to the Theory of Natural Selection, of which the title seems to reflect how he viewed himself: as a contributor to Darwin’s theoretical breakthrough. Wallace waited until 1889 to produce a full-length volume on the subject, that one abnegatingly titled Darwinism: An Exposition of the Theory of Natural Selection with Some of its Applications. He was an independent-spirited man but, excepting a few circumstances, he remained faithfully subordinate to Darwin and Darwin’s idea. The most notable exception came in early 1869, when Wallace unexpectedly dissented on a crucial point, asserting that natural selection couldn’t account for the human brain.

  Wallace’s apostasy may have reflected other changes in his own life and interests since returning to England. Always eclectic, impetuous in his enthusiasms, he had gotten interested in spiritualism and begun attending séances as an avid believer. During one spooky session with a medium, he’d heard his dead brother Herbert rap out a coded hello from the beyond. Spiritualism was enjoying a boom in popularity at the time, thanks presumably to its combination of vulgar metaphysics, nostalgia for the dearly departed, and parlor entertainment in an era before television. Some scientists saw it as a harmless fad, or else as contemptible bunkum, but to Alfred Wallace it was a new horizon in anthropology. Although not religious in any conventional sense, he concluded that there was more to this world than physical causes and effects. His new credence didn’t collide openly with his older views until April 1869, when The Quarterly Review carried an essay by him, mostly focused again on Lyell’s geology, in which Wallace pointedly digressed to the subject of natural selection. That mechanism couldn’t have produced the human brain, he wrote, let alone the “moral and higher intellectual nature of man.” Of course the living world is governed by laws, Wallace noted. But he himself was now inclined to believe “that an Overruling Intelligence has watched over the action of those laws, so directing variations and so determining their accumulation” as to yield the loftier, more wondrous human capacities.

  Darwin knew the article was coming and, a month earlier, had told Wallace with nervous good cheer: “I shall be intensely curious to read the Quarterly. I hope you have not murdered too completely your own & my child.” In the event, it was as bad as he feared: intellectual infanticide. Natural selection as Darwin (and Wallace too?) had originally conceived it was meaningless if “an Overruling Intelligence” overruled the haphazardness of the variations, directing them toward foreordained purposes. In the margin of his copy, Darwin scratched “No!!!”

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  Discomfort with natural selection, working crosswise to the general acceptance of evolution, pushed biologists during the late nineteenth century toward alternate explanatory mechanisms. Some of those biologists looked backward in time, and to France, for a revival of Lamarckism. Some embraced other evolutionary theories, various in their particulars but with enough common elements to be lumped under two labels, “orthogenesis” and “saltationism.” All three—orthogenesis, saltationism, and revived Lamarckism—came on strongly during the 1880s and 1890s, a slump period for Darwin’s reputation. A historian of evolutionary thought named Peter J. Bowler has nicely charted these currents in several of his books, including one titled The Eclipse of Darwinism. Bowler’s research corrects the misconception that, after publishing The Origin of Species, Charles Darwin rode to glory in a flaming chariot. No, he sat parked on a siding.

  The new Lamarckians didn’t entirely reject Darwin’s big idea, but they considered it small. Okay, they allowed, maybe natural selection does play a marginal role in fine-tuning adaptations, but it can’t explain the origin of variations or the dramatic trends and patterns of evolutionary change. Selective in their definition of Lamarckism, they also largely ignored Lamarck’s own woozy notions about “subtle fluids” and a “feeling of existence,” preferring two other items from his cornucopia of theory: the parallel progression of independent lineages from simple to complex (that is, the prairie-grass model of biological diversity, as opposed to the branching-tree model) and the inheritance of acquired characteristics. They emphasized the role of environmental conditions in eliciting need-directed variations (not undirected ones, as Darwin had it) which, so they believed, are heritable. They also inclined toward the view that long-term evolutionary trends are linear, triggered by environmental conditions and driven onward by habit, and by the inheritance of what habit produces. Horns get bigger, from species to species over millions of years, because animals use them when they smack heads. The fossil record yields other examples of such linearity, supposedly transcending the immediate adaptive needs of each individual creature and expressing inherent trends throughout the history of a lineage. Direct influences from the environment might account for the small-scale changes and adaptations, while continuous habit or some mysterious force drives the long-term trends.

  There was no perfect consensus, though, among the new Lamarckians. Paleontologists tended to see the long, linear trends; field naturalists and lab experimenters tended to see, or imagine they saw, the inheritance of acquired characteristics. The whole school of thought was especially strong in America, where a naturalist named Alpheus S. Packard, Jr., called it neo-Lamarckism.

  Packard, like other influential neo-Lamarckians of his generation, had been trained by Louis Agassiz, the Swiss-born naturalist who ruled in professorial majesty at Harvard’s Museum of Comparative Zoology. Agassiz was a brilliant but obdurate man, an essentialist who detested evolutionism—Darwin’s brand in particular—and clung to a vision of well-ordered nature assembled by special creations. The zoology of Agassiz was consonant with the natural theology of William Paley. Agassiz’s livelier students, such as Packard, did cross the line to accept evolution in principle, but even they mostly retained the old man’s distaste for Darwin’s cold, hard mechanism. Packard began seeing what he thought were Lamarckian phenomena during his study of the horseshoe crab, Limulus polyphemus. Then he turned to the blind insects and other dark-dwelling animals of Mammoth Cave, in Kentucky, concluding that their loss of eyesight (in some cases, of eyes altogether) results from disuse, followed by shrinkage of visual organs, followed by inheritance of the shrunken forms. Although Darwin himself had admitted a secondary role for use and disuse, the evidence from Mammoth Cave struck Packard as “Lamarckism in a modern form.” That explanation seemed to him “nearer the truth than Darwinism proper or natural selection.”

  Among the American paleontologists was another Alpheus (you can’t tell them without a scorecard), also trained at Harvard by Louis Agassiz: Alpheus Hyatt. From his study of ammonoids and other fossil invertebrates, Hyatt concluded that evolution is an additive developmental process—one that proceeds by the addition of new adult characteristics onto older sequences of development. Adding such characteristics, Hyatt thought, somehow compresses the more primitive traits backward into earlier embryonic stages. This idea became known as “the law of acceleration,” suggesting that speedier growth through the earlier stages allows for the additional complexity in adulthood. What’s the source of those newer, more complex characteristics? After some hesitation, Hyatt accepted the Lamarckian view that they are adaptive adjustments to environmental stresses, acquired as habits and then inherited.

  Edward
Drinker Cope, an American paleontologist working on vertebrate fossils, arrived at the law of acceleration independently. Like Hyatt, he saw long-term linear trends in fossil sequences—new modifications added onto older forms in a steady, directional way—and, again like Hyatt, became convinced that the inheritance of characteristics acquired in response to environmental conditions is what best explains them. In 1877, Cope published a book, The Origin of the Fittest, combining Darwin’s own title with Herbert Spencer’s vivid phrase (“the Survival of the Fittest”) to impute that Darwin hadn’t dug deeply enough into the subject. Like the other Alpheus—that is, Alpheus Packard—Cope granted that natural selection might play some part in culling inferior individuals, but he figured it couldn’t be more than secondarily important, because it didn’t explain the source of variation. Lamarckism, Cope thought, did.

  In England, Herbert Spencer himself had espoused a theory of evolution (he called it “the development hypothesis”) as early as 1852, seven years before Darwin’s book. Spencer was no biologist; he worked as a journalist, became prominent as a pop philosopher, and picked up his evolutionary ideas from reading Lyell’s dismissive account of Lamarckism (which turned him, perversely, toward Lamarck) and the mystery bestseller of the day, Vestiges. His own writings about evolution were grandiose and murky, detached from the sort of empirical detail that Darwin offered abundantly. But the subject gave Spencer’s works on political philosophy and sociology a yeasty fluff, especially when he linked his advocacy of laissez-faire individualism to notions of evolutionary progression; and he sold well. Some scholars credit (or blame) Spencer for launching the intellectual movement misleadingly known as Social Darwinism, and for transmitting it to America through his publications and, more personally, during a visit in 1882. The steel magnate Andrew Carnegie read both Spencer and Darwin, finding luminous reassurance in being told that harsh competition is a constructive law of nature. By then Spencer himself had emerged as a neo-Lamarckian, and arguably a social neo-Lamarckian, too. In a choice between natural selection of undirected variations, on the one hand, and heritable advantages gained through striving, on the other hand, the latter fit better with his ideas about self-advancement. Onward and upward for ambitious men and their scions! Eleven years after Darwin’s death, Spencer made it explicit with an essay titled “The Inadequacy of Natural Selection.”