by Carl Sagan
Lyell had been a lawyer for as long as he could stand it. When he was thirty years old, he abandoned the law for geology, his true passion. He wrote Principles of Geology to advance the “Uniformitarian” view that the Earth has been shaped by the same gradual processes that we observe today, but operating not merely over a few weeks, or a few thousand years, but ages. There were distinguished geologists who held that floods and other catastrophes might explain the Earth’s landforms, but that the Noachic flood wasn’t enough. It would take many floods, many catastrophes. These scientific Catastrophists were comfortable with Lyell’s long time scales But for the biblical literalists Lyell posed an awkward problem. If Lyell was right, the rocks were saying that the Bible’s six days of Creation, and the age of the Earth deduced by adding up the “begats,” were somehow in error It was through this apparent hole in Genesis that the Beagle would sail into history.
Hired mainly as FitzRoy’s companion and sounding board, Darwin was obliged to bear with equanimity the Captain’s politically conservative, racist, and fundamentalist harangues. For most of the voyage, the two men managed to maintain a truce with regard to their philosophical and political differences. However, Darwin was simply unable to let FitzRoy’s opinion on one particular issue go unchallenged:
[A]t Bahia, in Brazil, he defended and praised slavery, which I abominated, and told me that he had just visited a great slave-owner, who had called up many of his slaves and asked them whether they wished to be free, and all answered “No.” I then asked him, perhaps with a sneer, whether he thought that the answers of slaves in the presence of their master was worth anything? This made him excessively angry, and he said that as I doubted his word we could not live any longer together.13
Darwin fully expected to be kicked off the ship. But when the gunroom officers heard of the row, they vied with each other for the privilege of sharing their quarters with him. FitzRoy calmed down and actually apologized to Darwin, rescinding the eviction. Possibly, Darwin’s evolutionary views emerged, in part, out of his exasperation with FitzRoy’s inflexible conventionalism, and the necessity of the young man to suppress for five years the counterarguments that were welling up inside him14
Perhaps it was the legacy of his grandfathers that enabled Darwin to detect the inconsistencies and injustices that other members of his social class would not see. At the very beginning of his book, The Voyage of the Beagle, he tells of a place not far from Rio de Janeiro:
This spot is notorious from having been, for a long time, the residence of some runaway slaves, who, by cultivating a little ground near the top, contrived to eke out a subsistence. At length they were discovered, and a party of soldiers being sent, the whole were seized with the exception of one old woman, who, sooner than again be led into slavery, dashed herself to pieces from the summit of the mountain. In a Roman matron this would have been called the noble love of freedom: in a poor negress it is mere brutal obstinacy.15
Darwin had been lured to South America by the prospect of discovering new birds and new beetles, but he couldn’t help noticing the carnage the Europeans were inflicting. Colonial arrogance, the institution of slavery, the extirpation of countless species for the enrichment and entertainment of the invaders, the first depredations of the tropical rain forest—in short, many of the crimes and stupidities that haunt us today—troubled Darwin at a time when Europe was confident that colonialism was an unalloyed benefit for the uncivilized, that the forests were inexhaustible, and that there would always be enough egret feathers for every millinery shop until the Day of Judgment. In part because of these sensitivities, in part because Darwin always wrote as clearly and directly as he could—striving to communicate to the greatest number of people—The Voyage of the Beagle is still a stirring and accessible adventure story.
However, this book has watershed status because it was during the course of the expedition it recounts that Darwin began to amass the great body of evidence—not intuition, but data—that makes the case for evolution by natural selection. “At last gleams of light have come,” he was later to write, “and I am almost convinced that species are not (it is like confessing a murder) immutable.”
The Galapagos is an archipelago of thirteen good-sized islands and many smaller ones lying off the coast of Ecuador. If all the species on Earth were immutable, then why did the beaks of the otherwise very similar finches on islands separated by no more than fifty or sixty miles of ocean vary so dramatically? Why narrow, tiny, pointy beaks on the finches of one island and larger, parrot-like curved beaks on the finches of the next? “Seeing this gradation and diversity of structure in one, small intimately related group of birds,” he later wrote in The Voyage, “one might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.” (These volcanic islands, we now know, are less than 5 million years old.) And it wasn’t just the finches that raised such problems, but the giant tortoises and the mockingbirds, too.
Back in England, Henslow and Sedgwick had been reading Darwin’s letters aloud at meetings of scientific societies. When Darwin returned home in October 1836, he found he had acquired something of a reputation as an explorer and naturalist. His father was now well pleased with him, and all talk of a parsonage ceased. The same month he met the geologist, Lyell, for the first time. Though not without its rough spots, it was to be a lifelong friendship.
Darwin made important contributions to geology. His interpretation of coral reefs—that they mark the locations of slowly subsiding sea-mounts that had once been islands—was substantiated on the Beagle and corresponds to the modern understanding. In 1838 he published a paper arguing that earthquakes, volcanoes, and the thrusting up of islands are all caused by slow, intermittent, but irresistible global motions in the semi-liquid interior of the Earth. This “almost prophetic”16 thesis, as far as it goes, is part and parcel of modern geophysics. In his 1838 Presidential Address to the Geological Society, William Whewell mentioned Darwin’s name (in the context of this work) more than twice as often as any other geologist, living or dead. In geology, following Lyell, as in biology, Darwin championed the idea that profound changes are worked little by little over vast intervals of time.
In 1839, he married his cousin, Emma Wedgwood. Through ten children and more than four decades they shared a deep, loving, and almost entirely harmonious relationship. During their early married life he was writing down, but certainly not for publication, his first tentative sketch for a theory of evolution. Their rare differences were over religion. “Before I was engaged to be married,” he wrote in his autobiography, “my father advised me to conceal carefully my doubts, for he said that he had known extreme misery thus caused with married persons.”17 A few weeks after their wedding, she wrote to him:
May not the habit in scientific pursuits of believing nothing till it is proved influence your mind too much in other things which cannot be proved in the same way, and which if true are likely to be above our comprehension?
Years later, Darwin wrote at the bottom of Emma’s letter,
When I am dead, know that many times,
I have kissed and cried over this.18
He tried his best to avoid the public version of this domestic tension. Our past was then a dark and shameful secret. To expose it would have been perceived by many as an affront to the prevailing religious norms and as an assault against human dignity. But to suppress it would have been to reject the data because the implications were disturbing. Darwin recognized that if he was to convince anyone he would have to support his argument with a compelling body of evidence.
In 1844, a sensational book, fundamentally pseudoscience, called Vestiges of the Natural History of Creation was published. Robert Chambers, the encyclopedist and amateur geologist who was its anonymous author, claimed that he had traced human ancestry all the way back to … frogs. Chambers’ reasoning was half-baked (although no more so than Erasmus Darwin’s) but its audacity attracted a grea
t deal of attention. Nagging doubts about Creation were beginning to bubble to the surface, and Darwin felt that he should write down his own theory in as irrefutable a form as possible. He expanded a short essay, begun two years before, into a two-part work entitled “On the Variation of Organic Beings under Domestication and in the Natural State” and “On the Evidence Favourable and Opposed to the View That Species Are Naturally Formed Races Descended from Common Stock.” However, he was not ready to publish. He wrote a letter to Emma that he asked be considered as a codicil to his will. In the event of his death, he wanted her to
devote £400 to its publication and further will yourself … take trouble in promoting it—I wish that my sketch be given to some competent person, with this sum to induce him to take trouble in its improvement and enlargement.19
He felt he was on to something important, but feared—perhaps especially in view of his frequent bouts of illness—that he would not live to complete the work.
In what superficially seems an odd next move, he now put his evolutionary studies aside and for the next eight years devoted his life almost exclusively to barnacles. His great friend, the botanist Joseph Hooker, would later observe to Darwin’s son, Francis, “Your father had Barnacles on the brain from Chili [Chile] onwards!”20 It was this exhaustive project that really earned him his credentials as a naturalist. Another close friend, the anatomist and brilliant polemicist Thomas Henry Huxley, observed that Darwin
never did a wiser thing … Like the rest of us, he had no proper training in biological science, and it has always struck me as a remarkable instance of his scientific insight, that he saw the necessity of giving himself such training, and of his courage, that he did not shirk the labour of obtaining it … It was a piece of critical self-discipline, the effect of which manifested itself in everything [he] wrote afterwards, and saved him from endless errors of detail.21
Darwin had not been the only scientist to get a jolt from Chambers’ Vestiges. Alfred Russel Wallace, a surveyor who had become a naturalist, was also unimpressed with Chambers’ arguments, but also intrigued by the notion that there was a knowable process at work in the evolution of life. In 1847, he traveled to the Amazon in search of factual support for this idea. A fire on the ship taking him back to England consumed every one of his specimens. Wallace persevered, setting off to the Malay Peninsula to gather a new collection. In the September 1855 issue of Annals and Magazine of Natural History, his paper “On the Law Which Has Regulated the Introduction of New Species” appeared.
By this time, Darwin had been wrestling with such problems for two decades. Now, it was entirely possible that his claims of priority to the solution of life’s greatest mystery would be snatched away. If science were in the business of conferring sainthood, the conduct of Darwin and Wallace towards one another would have earned it for them both. Darwin wrote a letter of hearty congratulation to Wallace in which he mentioned how long he’d been working on the same problem.
Darwin’s friends Huxley and Hooker prodded him to quit stalling and write the paper that would make an ironclad case for evolution. He complied and was nearing its completion in 1858, while Wallace, now in Indonesia and sick with malaria, tossed and turned, grappling with the question “Why do some die and some live?”22 Emerging from his stupor, he understood natural selection. He wrote “On the Tendency of Varieties to Depart Indefinitely from the Original Type” and promptly mailed it to Darwin, asking him to use his judgment about what should be done with it. Darwin was distressed to see how very close Wallace’s work was to his own writings of 1839 and 1842. In 1844 he had combined them into an essay, but it remained unpublished. Darwin turned to his friends for guidance on how to deal ethically with this dilemma. Hooker and Lyell came up with a wise solution: Present both the Wallace paper and a version of Darwin’s unpublished 1844 essay at the next meeting of the Linnaean Society and publish them together in the Society’s Proceedings.23 Thereafter, Wallace always spoke of evolution as being Darwin’s theory and Darwin always credited Wallace with its independent discovery. Darwin now applied himself to the task of writing the book that would cause so much trouble.
On November 24, 1859, The Origin of Species was published. The first edition of 1,250 copies was snapped up by the booksellers. Darwin had been careful to make only one reference to humans in the whole book: “Light will be thrown on the origin of man and his history.”24 Anything more from his pen on this delicate matter would have to wait another twelve years, for the publication of The Descent of Man. His restraint fooled no one. Given its formidable armamentarium of data, there could be no reconciling The Origin with a literal rendition of Genesis.
Chapter 4
A GOSPEL OF DIRT
I detest all systems that depreciate human
nature. If it be a delusion that there is
something in the constitution of man that is
venerable and worthy of its author, let me live
and die in that delusion, rather than have my
eyes opened to see my species in a humiliating
and disgusting light. Every good man feels his
indignation rise against those who disparage his
kindred or his country; why should it not rise
against those who disparage his kind?
THOMAS REID
letter of 17751
When I view all beings not as special creations,
but as the lineal descendants of some few
beings which lived long before the first bed of
the Cambrian [geological] system was
deposited, they seem to me to become
ennobled.
CHARLES DARWIN
The Origin of Species, Chapter XV2
Mankind has conducted an experiment of gigantic proportions,” Darwin wrote in The Origin of Species. He was struck by the success of “husbandry,” as it is tellingly called, in generating new varieties of animals and plants useful for humans. Nature provides the varieties and we select who shall reproduce, which traits we want preferentially to propagate into future generations. By transferring pollen from flower to flower with a camel’s hair brush, or by letting the stallion in with the mare, humans take it upon themselves to determine who shall mate with whom. Indigestible crops, weakling horses, scrawny turkeys, sheep with knotty coats, and cows that are grudging with their milk are discouraged from reproducing. Generation after generation, by cumulative selection, humans impress their interests on the heredity of the plants and animals whose breeding they control. But Nature, too, selects those plants and animals which by its lights happen to be more favorably adapted than their fellows; such fortunate beings preferentially reproduce, leave more offspring and, as time goes on, supplant the competition. Artificial selection helps us to understand how natural selection works.
The ability of the environment to nurture and sustain large populations—the so-called carrying capacity—is of course finite. As the number of organisms increases, not all will be able to survive. There will be a stringent competition for scarce resources. Slight differences in ability, imperceptible to a casual observer, may spell life or death to the organism. Natural selection is a great sieve, straining out the vast majority and permitting only a tiny vanguard to pass its heredity on to the next generation. Natural selection is far more ruthless than the most callous and resolute animal breeder in determining the genetic makeup of future generations. And instead of the measly few thousand years since the domestication of animals began in earnest, natural selection has been working for billions.
Consider the diverse specializations that, through artificial selection, we’ve generated in dogs—greyhounds and borzois for speed, to outrun the wolves; collies for herding sheep; beagles, pointers, and setters for hunting; Labrador retrievers for helping fishermen gather their nets; guide dogs for the blind; bloodhounds for tracking criminals; terriers for worrying prey out of burrows; mastiffs for guard duty; and the original Pekinese (of which only a dwarf remnant remains) for wa
r. We did all that, in only a few thousand years, by meddling with the sex lives of dogs. We evolved cauliflower, rutabaga, broccoli, brussels sprouts, and the now common and luxuriant cabbage from the sorry wild cabbage (these vegetables, like the different breeds of dogs, remain interfertile). Now think of a much more rigorous, much more stringent selection operating on all of Nature over an expanse of time a million times longer—and established not by the conscious meddling of dog or plant breeders with some idea of what kind of dog or plant they’re aiming for, but by a blind, purposeless, and changing environment. If artificial selection represents an experiment of gigantic proportions, what must be the dimensions of the experiment that natural selection has performed? Isn’t it plausible that all the elegantly adaptive diversity of life on Earth could thereby be sifted and extracted? Indeed, it is the only known process that adapts organisms to their environments.3
Here are the passages from Darwin’s Origin of Species in which he first develops the point and counterpoint of artificial and natural selection:
One of the most remarkable features in our domesticated races is that we see in them adaptation, not indeed to the animal’s or plant’s own good, but to man’s use or fancy. Some variations useful to him have probably arisen suddenly, or by one step … But when we compare the dray-horse and race-horse, the dromedary and camel, the various breeds of sheep fitted either for cultivated land or mountain pasture, with the wool of one breed good for one purpose, and that of another breed for another purpose; when we compare the many breeds of dogs, each good for man in different ways; when we compare the game-cock, so pertinacious in battle, with other breeds so little quarrelsome, with “everlasting layers” [of eggs, which never desire to sit, and with the bantam so small and elegant; when we compare the host of agricultural, culinary, orchard, and flower-garden races of plants, most useful to man at different seasons and for different purposes, or so beautiful in his eyes, we must, I think, look further than to mere variability. We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we now see them; indeed, in many cases, we know that this has not been their history. The key is man’s power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to have made for himself useful breeds.