Buried evidence of geological upheaval was depicted in cutaway drawings like this one in Hutton’s Theory of the Earth. (After Hutton, 1795.)
The inaugural fortunes of uniformitarianism suffered, moreover, from the liabilities of Hutton’s literary style; his Theory of the Earth, published in 1795, was written in a syntax as jumbled as the strata it described. The situation improved somewhat when John Playfair took the trouble to elucidate his friend Hutton’s views, in his Illustrations of the Huttonian Theory of the Earth, but the real breakthrough came a generation later, when the uniformitarian hypothesis was taken up by Lyell. Born in 1797, the year of Hutton’s death, Lyell was an energetic young man, blessed with poor eyesight, who peered at the world around him with myopic intensity. While still an undergraduate studying geology at Oxford, Lyell took a holiday trip to a spot on the seashore that he had visited as a child, and he noticed, as many another bather had not, that erosion had slightly altered the shape of the coastline near Norwich. He began to conceive of the planet as a seething, changing entity, writhing in its own good time like a living organism.
Much of the prior debate over the age of the world had been conducted from easy chairs, by the likes of the English divine Thomas Burnet, who boasted that he based his efforts to reconcile scientific and biblical accounts of history on but three sources, “Scripture, Reason, and ancient Tradition.”‘12 Lyell spent his days wandering to and fro upon the earth, and in his sixties was still scrambling up mountainsides and down dry washes, making notes all the while. Mount Etna in Sicily, the traditional abode of Vulcan’s forge, had long been a favorite subject of studious scholars who had viewed it, if at all, from afar. Lyell climbed its slopes of freshly frozen lava, and deduced, from his measurements of the sheer bulk of the ten-thousand-foot mountain, that it had been built up from a great many lava flows, the accumulation of which “must have required an immense series of ages anterior to our historical periods for its growth.”13 In Chile, Lyell estimated that a single earthquake could elevate the coastal mountains by as much as three feet, and speculated that “a repetition of two thousand shocks, of equal violence, might produce a mountain chain one hundred miles long and six thousand feet high.”14 The identification of warm-water seashells in northern Italy and of the bodies of mammoth frozen in Siberian ice, he noted, indicate that the European climate was once “sufficiently mild to afford food for numerous herds of elephants and rhinoceroses, of species distinct from those now living” (Lyell’s italics).15
A lucid and vivid writer, Lyell was as adept at demolishing the arguments of the catastrophists as he was at comprehending the construction of mountain ranges. “Geologists have been ever prone to represent Nature as having been prodigal of violence and parsimonious of time,” he wrote, but, he noted, the fracturing and weathering of rock taken by the catastrophists to represent the violence of the early Earth could as easily have been imposed by the ravages of time.16 A voracious student of biology as well as geology (his father had been a botanist, and Lyell fils had studied entomology) he drew upon the life sciences as well. The catastrophists relegate extinction to brief cataclysms, he wrote, but
if we then turn to the present state of the animate creation, and inquire whether it has now become fixed and stationary, we discover that, on the contrary, it is in a state of continual flux—that there are many causes in action which tend to the extinction of species, and which are conclusive against the doctrine of their unlimited durability.’17
It is true, as the catastrophists point out, that the fossil record is fragmented and broken. But, Lyell argued, disastrous events were not required to break it:
Forests may be as dense and lofty as those of Brazil, and may swarm with quadrupeds, birds, and insects, yet at the end of ten thousand years one layer of black mould, a few inches thick, may be the sole representative of those myriads of trees, leaves, flowers, and fruits, those innumerable bones and skeletons of birds, quadrupeds, and reptiles, which tenanted the fertile region. Should this land be at length submerged, the waves of the sea may wash away in a few hours the scanty covering of mould.18
If Lyell was right in concluding that “the causes which produced the former revolutions [i.e., dramatic changes] of the globe” were the same as “those now in everyday operation,” then the age of the earth must be reckoned not in thousands but in millions of years.19
But the choice, Lyell argued, was not solely between a young and an old Earth. Nor was it a clear-cut case of catastrophism versus uniformitarianism (each of which would in any case prove to contain seeds of the truth). The real choice was between a closed science, resigned to turn a blind eye on any evidence that contradicted the existing consensus, and an open science that dared to follow the evidence toward unknown inferences. If the first path, as Lyell wrote, was “calculated … to blunt the keen edge of curiosity,” the second “cherishes a sanguine hope that the resources to be derived from observation and experiment, or from the study of nature such as she now is, are very far from being exhausted.”20
In December 1831 the young man who would journey farthest along the road leading into the depths of time was packing his bags to depart on a voyage around the world, with a copy of the first volume of Lyell’s Principles of Geology in his portable library. The book, published the previous year, had been recommended by his friend and teacher John Henslow. A catastrophist like virtually every other geologist at the time, Henslow advised his former student to enjoy Lyell’s writing, but cautioned him on no account to take its radical views seriously. Charles Darwin cheerfully agreed, packed the book, and set sail on the Beagle.
*Aristotle explained fossil fish by postulating that the fish had got stranded and died while foraging for food in subterranean caverns.
13
THE AGE OF THE EARTH
The antiquity of time is the youth of the world.
—Francis Bacon
What we take for the history of nature is only the very incomplete history of an instant.
—Denis Diderot
Lyell’s book turned Darwin’s voyage into a trip through time. Darwin began reading it almost immediately, in his bunk, while suffering through the first of the many attacks of seasickness that were to plague him during the next five years—the Beagle, a stout, beamy brig ninety feet long by twenty-four feet wide, was otherwise comfortable, but her hull was rounded and she rolled. He started applying what he called “the wonderful superiority of Lyell’s manner of treating geology”1 as soon as the expedition made landfall in the Cape Verde islands.
To construct an empirically based theory like Darwin’s account of evolution requires not only observational data but an organizing hypothesis as well. Darwin drew his hypothesis—that the world is old, and is continuing to change today much as it did in the past—largely from Lyell. “The great merit of the Principles,” he wrote, “was that it altered the whole tone of one’s mind, and, therefore, that when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.” Later Darwin allowed that “I feel as if my books came half out of Sir Charles Lyell’s brain.”2
The observations Darwin himself was well suited to provide. “Nothing escaped him,” wrote Dr. Edward Eickstead Lane, who often walked with Darwin at Moor Park.
No object in nature, whether Flower, or Bird, or Insect of any kind, could avoid his loving recognition. He knew about them all … could give you endless information … in a manner so full of point and pith and living interest, and so full of charm, that you could not but be supremely delighted, nor fail to feel … that you were enjoying a vast intellectual treat to be never forgotten.”3
During the Beagle expedition Darwin saw the world as few have seen it, in rich diversity and detail, from horseback and muleback and on foot, in cave explorations and excursions across pack ice and blazing sand from Patagonia to Australia to the Keeling Islands of the Indian Ocean. He noted everything, absorbed everything, and collected so many samples of plants and animals that his shipmates wondered
aloud whether he was out to sink the Beagle.
In Chile, Darwin found marine fossils on mountaintops twelve thousand feet high and witnessed an earthquake that raised the ground three feet in a matter of minutes—Lyellian evidence that the more or less uniform operation of geological processes can produce changes as dramatic as those ascribed by the theologians ancient catastrophes. At first he was cautious about jumping to conclusions: Reporting his findings in a letter to his teacher Henslow he wrote that “I am afraid you will tell me to learn my A.B.C.—to know quartz from Feldspar—before I indulge in such speculations.”4 But by the time the Beagle reached the South Pacific, Darwin had four years of rigorous fieldwork under his belt, and had begun to feel more confident of his ability to interpret observations in terms of hypotheses.
There he ventured an ingenious theory of his own, concerning the origin of coral atolls. On a hot fall day in 1834, while the Beagle was making headway from the Galapagos Islands toward Tahiti, he climbed the mainmast and saw the bone-white atolls of the Dangerous Archipelago scattered across the sea like so many lacy hoops. He was impressed by their appearance of frailty: “These low hollow coral islands bear no proportion to the vast ocean out of which they abruptly rise,” he wrote, “and it seems wonderful, that such weak invaders are not overwhelmed, by the all-powerful and never-tiring waves of that great sea, miscalled the Pacific.”5
Darwin theorized that the atolls marked the sites of vanished volcanos.* A new volcano can burst through the sea floor and, in successive eruptions, build itself up into a mountainous island that towers above the sea. When the lava stops flowing and things quiet down, a live coral reef can form on the flanks of the volcano, just below sea level. Here begins Darwin’s contribution: Eventually, he said, the inactive volcano may begin to sink, owing either to erosion or to the slow collapse of the ocean floor. As the old island gradually subsides, live coral continues to build up atop the dead and dying coral below. Eventually the original island vanishes beneath the waves, leaving a ring of coral behind. “The reef constructing corals,” Darwin wrote, “have indeed reared and preserved wonderful memorials of the subterranean oscillations of level; we see in each barrier-reef a proof that the land has there subsided, and in each atoll a monument over an island now lost.”6
The beauty of this theory, from a uniformitarian standpoint, was that the process had to be gradual. Living coral requires sunlight; as Darwin noted, it “cannot live at a greater depth than from twenty to thirty fathoms,” or some 120 to 180 feet.7 Had the islands sunk rapidly, as catastrophism demanded, the coral would have been plunged into the dark depths of the sea before new coral had time to grow on top of it, and no atoll would have been left behind.
When Darwin returned home after five years aboard the Beagle, his father upon first laying eyes on him “turned round to my sisters and exclaimed, ‘Why the shape of his head is quite altered.’”8 This was something of a family in-joke; phrenology and physiognomy were Victorian passions that Robert Darwin shared with Robert Fitz-Roy, captain of the Beagle, who had at first refused to hire on the young Darwin owing to what Fitz-Roy took to be the inauspicious shape of his nose. But the elder Darwin was a sensitiveobserver, and his remark reflected his awareness that a lot had changed inside his son’s skull as well. This was cause for celebration, for the young Darwin had been an idle and seemingly vacant lad with a passion for riding, hunting, gambling, drinking, and collecting twigs and stones. “You care for nothing but shooting, dogs, and rat-catching, and you will be a disgrace to yourself and all your family,” his father had complained, to the delight of many a future biographer.9 Darwin had dropped out of medical school, disappointing his father, who was a respected physician, and had failed to distinguish himself even in the undemanding theological studies to which he had been dispatched with the intention of preparing him for sinecure as a country parson.
Darwin’s account of the origin of the atolls held that as a mountain in the sea subsides, live coral continues to build up along what once were its coasts, until the ring of coral is all that remains.
The changes that led to a berth on the Beagle commenced at Cambridge. There Darwin became acquainted with Adam Sedgwick, one of the world’s most accomplished field geologists, took courses in botany from Henslow, who combined an acutely rational mind with a buoyant outlook worthy of Linnaeus, and began to realize that he might, through science, combine his powers of observation with his love for the outdoors and his propensity for collecting. “I discovered,” he wrote years later, “though unconsciously and insensibly, that the pleasure of observing and reasoning was a much higher one than that of skill and sport. The primeval instincts of the barbarian slowly yielded to the acquired tastes of the civilized man.”10
When Darwin left England he was still a creationist. He did “not then in the least doubt the strict and literal truth of every word in the Bible,” he recalled, and he believed, as did most of the geologists and biologists of his day, that all species of life had been created simultaneously and individually.11 He returned home with doubts on this score. He had seen firsthand evidence that the earth is embroiled in continuing change, and he wondered whether species might change, too, and whether their mutability might cause new species to come into existence.
Evolution in itself was not a new idea. As a boy Darwin had read with interest his grandfather Erasmus Darwin’s book Zoonomia, an evolutionary treatise full of robust exclamations over the notion that all life could have evolved from a single ancestor:
Perhaps millions of ages before the commencement of the history of mankind, would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality …? What a magnificent idea of the infinite power of THE GREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS!’12
Darwin was familiar, too, with the evolutionary views of the French biologist Jean-Baptiste de Lamarck, who maintained that traits acquired by individuals through experience could be passed on to their offspring. In a Lamarckian world, horses who grew strong through racing bequeathed their fleetness to their young, while giraffes, by stretching their necks to reach the leaves on trees, made the next generation of giraffes more long-necked. Lamarckism was replete with moral overtones gratifying to the Victorians, since it implied that parents who worked hard and avoided vice would have children who were genetically disposed toward hard work and clean living. But it foundered on the question of how new species had arisen. It pointed the way to ever better horses and giraffes, but not to the origin of species, and thus left unanswered the question of why different species are found in the fossil record than are living today.
Darwin’s contribution was not simply to argue that life had evolved—he did not even like to use the word “evolution”—but rather to identify the evolutionary mechanism by which new species come into existence. That was why he titled his book The Origin of Species. His theory can be outlined in terms of three premises and a conclusion.
The first premise has to do with variation. It notes that each individual member of any given species is different—that each, as we would say today, has a distinct genetic makeup. Darwin understood this very well. He grew up at a time when animal breeding and plant hybridization was booming in England—his father-in-law, Josiah Wedgwood, the ceramics manufacturer, was a noted sheep breeder, and his father was a pigeon fancier—and he learned from the husbanders to pay attention to the often subtle individual characteristics that they sought to quash or to perpetuate.* Grounded in the specifics of biological variety, Darwin’s thought was a mosaic of the particular: Scores of his publications consists of little notes in the Gardeners’ Chronicle and Agricultural Gazette and the Journal of Horticulture and Cottage Gardener asking such questions as, “Has any one who has saved seed Peas grown close to other kinds observed that the succeeding crop came up untrue or crossed?”13 and, “Is any record kept of the diameter attained by the largest Pansies?”14
Darwin’s
second premise is that all living creatures tend to produce more offspring than the environment can support. It’s a cruel world, in which only a fraction of the wolves and turtles and dragonflies that come into existence manage to find sustenance and avoid predators long enough to reproduce. The English economist Thomas Malthus had quantified these harsh facts of life by pointing out that most species reproduce geometrically, while the environment can support no better than a linear increase in their populations.* Darwin read Malthus’s An Essay on the Principle of Population in London in 1838—“for amusement,” he recalled—and the hypothesis of evolution by natural selection began to take form in his mind. “One may say,” he wrote, that “there is a force like a hundred thousand wedges trying [to] force every kind of adapted structure into the gaps in the [e]conomy of nature, or rather forming gaps by thrusting out weaker ones.”15 It was in the combination of the boundless fecundity of living things with the limited resources available to support them that Darwin found a natural, global mechanism that worked constantly to extinguish most variations, preserving only those carried by individuals who managed to survive and reproduce.
Which leads to the third premise—that the differences among individuals, combined with the environmental pressures emphasized by Malthus, affect the probability that a given individual will survive long enough to pass along its genetic characteristics. This is the process that Darwin called “natural selection.” White moths fare better in snow, where their coloration serves as camouflage and protects them from predator birds, while brown moths do better in snowless autumnal forests, where their color blends in against the brown tree trunks.* It is in this sense that the “fittest” (the phrase is Herbert Spencer’s) survive, not because they are in some sense superior to their colleagues, but because they better “fit” their environment. When environmental conditions change, the most exquisitely adapted individuals may suddenly find themselves no longer fit; then it is the freaks and misfits who inherit the future.
Coming of Age in the Milky Way Page 24
