The Reluctant Mr. Darwin (21 page)

For better and worse, with its flaws and its majesties,
The Origin of Species
stands as Darwin's ultimate statement of his theory, and the 1859 edition articulates that statement most freshly and boldly. It was never supplanted by the encyclopedic tome,
Natural Selection
, that he had intermittently intended to write. Through those five later editions of
The Origin
, he continued monkeying with his text, sometimes improving it but often just adding confusion, caution, and unnecessary words. By 1869, he sounded weary of that. “If I lived twenty more years and was able to work, how I should have to modify the
Origin
,” he confided to his dear old friend Hooker—and then, changing moods, mustering resoluteness, “how much the views on all points will have to be modified!” But he wouldn't live twenty more years. Nor did he expect to. So he sighed: “Well, it is a beginning, and that is something….”

It was something indeed: less than the book he had hoped to write, but more than enough to cause a ruckus.

1860 to the future

36

M
ost people today don't realize that natural selection, Darwin's greatest and most troubling idea, fell into disfavor among evolutionary biologists for fifty or sixty years. Most people imagine that the Darwinian revolution, so called, was a relatively quick campaign fought and won in the late nineteenth century. It wasn't. It was an up-down-up scuffle for decades.

There were two principal questions, contested almost independently: (1) Has evolution occurred? and (2) Is natural selection its main causal mechanism? Despite some horrified outcries from religious leaders and pious scientists, the descent of all species (even humans) from common ancestors became widely accepted rather soon after
The Origin of Species
was published. Despite his careful arguments in the first half of the book, Darwin's hypothesis as to the causal mechanism did not. Why not? Because the idea of natural selection seemed profoundly materialistic and gloomy—that is, it was both literally and figuratively dispiriting—whereas the idea of evolution seemed merely insulting (as applied to the human species) and bizarre. Evolution contradicted William Paley's natural theology, as propounded in 1802, yes; but Paley's natural theology was an ingenuous, prescientific vision that had outlived its time (except in America, where it returned during the late twentieth century under the label “Intelligent Design”) and was soon supplanted by the idea that species, rather than being individually created by God, had somehow evolved one from another. Natural selection struck deeper, undermining the whole notion of godly purpose. Evolution could be reconciled with belief that a divine Creator had established laws governing the universe, had set life into motion, had allowed species to change over time, and then—at some magical moment—had injected a unique spiritual dimension into the primate species that was later to be known (by its own self-naming) as
Homo sapiens
. Natural selection, on the other hand, seemed to preclude that belief. It did, anyway, if taken strictly and seriously—the way Charles Darwin took it.

The crux of the matter was not natural selection itself but the variations upon which it works. What causes those small differences between parents and offspring, and between one competing individual and another, which serve as the raw material for adaptive change? What laws govern their scope, rate of occurrence, and character? Are they purely random, or somehow constrained by limits of physical possibility—or are they, maybe, directed toward certain purposes by a higher power? If variations are random, then purposefulness (the philosophers of science call it teleology) disappears from the living world. Gone, zero, zip.

Whoa. That's a large step into darkness. No higher purpose to the vast pageant of life and death? No higher purpose to Herschel's “mystery of mysteries,” the first appearance of new species? No higher purpose behind adaptation and diversification, the processes whereby simplicity gives way to complexity on a spectrum from primal ooze to humans? These were implications that Darwin's nineteenth-century audience found difficult to accept. They're still difficult to accept. But this generalized loss of teleology is abstract and impersonal. It's not the source of keenest discomfort with natural selection. Another corollary of the theory is more acutely problematic: loss, for the human species, of our own special status as God's chosen.

Is there a glorious end for which evolution has produced mankind? Are humans in any sense uniquely ordained? Did the deity foresee we were coming and somehow will it? Or are we merely the most well adapted, cerebral, and successful species of primate that has ever lived? Beneath those questions lies one deeper question about the variations from which natural selection has shaped
Homo sapiens
: What is their source?

Darwin proposed in
The Origin
that variations occur in response to “conditions of life”—that is, external stresses such as severity of climate, food shortage, or habitat disturbance, which somehow unsettle the reproductive system. It was a calculated guess. Elsewhere in the book, he admitted: “Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part differs, more or less, from the same part in the parents.” Scholars have noticed this lacuna: His theory depends on variations, but there's no good account of their origin in
The Origin
. He just didn't know where they came from, nor how. At the time, no one did.

Puzzled as Darwin was about their source, he strongly suggested that variations are, overall, directionless. That is, they go here and there, haphazardly. They are scattershot, not aimed. The point is so crucial, and the language by which he addressed it so tricky, that it deserves a moment's special attention. Back in 1844, in his unpublished 189-page draft of the theory, Darwin had written that variations occur “in no determinate way.” Earlier still, in one of his notebook jottings, he had described them as “accidents.” He wrote in
The Origin
of “chance” variations, then noted elsewhere in the book that to say they are “due to chance” is an incorrect expression, a convenience of speech that merely “serves to acknowledge plainly our ignorance of the cause” of each one. It's an incorrect expression, he meant, in that variations do have physical
causes
; they just don't have preordained
purposes
. For instance, a drought might increase the rate of variation in a species, he thought, without necessarily evoking any particular variations that improve a creature's tolerance for drought. Or the drought might yield one variation for drought tolerance plus five others that are useless or harmful. If so, natural selection would tend to preserve and multiply that one. Selection is directional; variation, offering raw material to the selection process, is not directional.

But if variations are undirected, and if natural selection calibrates only the fitness of each individual creature to survive and reproduce, then is it possible to believe that God created humans in His image and likeness, endowing us with a spiritual dimension not shared by the best-adapted orchid or barnacle? Arguably not. There's a genuine contradiction here that can't easily be brushed away. But let's be clear: This is not evolution versus God. The
existence
of God—any sort of god, personal or abstract, immanent or distant—is not what Darwin's evolutionary theory challenges. What it challenges is the supposed godliness of Man—the conviction that
we
above all other life forms are spiritually elevated, divinely favored, possessed of an immaterial and immortal essence, such that we have special prospects for eternity, special status in the expectations of God, special rights and responsibilities on Earth. That's where Darwin runs afoul of Christianity, Judaism, Islam, and probably most other religions on the planet.

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.

37

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.