Natural Selection Unsealed

Darwin began by addressing some doubts that Joseph Hooker had raised. One of Darwin’s claims was that the plants and animals living on islands had not been created there, that they were modified descendants of colonists. If that were true, then they needed a way to get to the islands in the first place. Hooker, a seasoned botanist, knew that seeds could travel for miles by wind or water, but he doubted that they could travel the enormous distances that Darwin claimed.

Darwin met Hooker’s doubts by throwing seeds into tanks of saltwater and found that they could be soaked for four months and still sprout when he planted them in dry ground. He discovered that birds could carry seeds on their feet, and that seeds could even survive being eaten by owls, passing out of their bodies with their droppings. Darwin’s theory had generated a hypothesis, and the hypothesis passed a test.

Darwin also went back to his studies of breeding. He drank gin with pigeon breeders as they explained to him how to use tiny variations to produce entirely new forms of birds. Darwin raised pigeons of his own, killing them and boiling the flesh off their skeletons so that he could measure the variability among them. He found that each breed was so distinct that if it were wild, it would be considered its own species. Almost every part of a pigeon’s anatomy was distinct from that of other varieties, from their nostrils to their ribs to the size and shape of their eggs. And as far as anyone could tell, every pigeon variety descended from a single kind of wild rock dove.

By 1856 Darwin had found so much more evidence for evolution that he reopened his 1844 essay and began reworking it. It soon puffed up into a monstrous opus, running hundreds of thousands of words long. He threw in everything he had learned over the years–on his voyage, from his reading and conversations, from his studies on barnacles and seeds. He was determined to wear down the opposition with a river of facts.

Since the day that Charles had shown Emma his manuscript in 1844, he had barely spoken of his theory. But now he felt more confident revealing it to a few people–particularly to younger minds more open to new possibilities. For one of his initiates, he chose a brilliant, struggling young zoologist he had recently befriended, by the name of Thomas Huxley.

Huxley could not practice Darwin’s brand of gentlemanly science. He had been born above a butcher’s shop. His father, a teacher at a failed school and then a director of a failed bank, had no money for Huxley’s education. Huxley became a doctor’s apprentice at age 13 and three years later followed him down to London, where he was trained as a surgeon, barely getting by on scholarships and paltry loans from in‑laws. The only way he could pay off his debts was to join the crew of HMS Rattlesnake, a ship bound for the coasts of New Guinea, as an assistant surgeon. Huxley was developing a taste for zoology, and on the voyage he would be free to gather as many exotic species as he wanted.

After four years, Huxley returned to England in 1850, and like Darwin he had been transformed into a scientist by the journey. Like Darwin, he was preceded home by his reputation, with papers already published by the time he arrived, about bizarre creatures such as the Portuguese man o’ war, an animal that is actually a colony of individuals. Huxley arranged a special post with the Royal Navy, with three years’ leave with pay, so that he could continue his research. Without any degree, he was elected to the Royal Society at age 26.

The navy ordered Huxley three times to return to active duty, and the third time he refused they struck him from the list. He struggled to find other work in London and eventually ended up working parttime at the School of Mines. By writing columns and reviews on the side, he earned barely enough money for his family. Huxley resented the wealthy men who dominated science simply because they could afford to. But he managed nevertheless to build a reputation for himself and he wasn’t afraid to attack the dean of English biologists, Richard Owen.

Owen at the time was toying with the idea of a kind of divine evolution. Over time, he proposed, God made new species, always referring to His archetypes for their basic design. Owen pictured a stately unfolding of life according to a divine plan, moving from the general to the specialized: an “ordained continuous becoming.” To calm Owen’s patrons, who still clung to the comfort of natural theology and the fixity of species, he promised that biology was still “connected with the loftiest of moral speculations.”

In public lectures and in reviews, Huxley mocked Owen’s attempts to make God into a draftsman, and to make the fossil record read like His revisions. Huxley didn’t accept evolution in any form, whether divinely guided or simply materialistic. He saw no progress in the history of Earth or of life. But that changed when Darwin invited Huxley to come out to the country one weekend in 1856.

Darwin explained his version of evolution, one that could account for the patterns of nature without resorting to providence or special intervention. He showed Huxley his pigeons and seeds. Soon Huxley was persuaded, and would prove to be Darwin’s greatest ally.

Darwin’s slow, cautious march toward a public declaration was moving along well, until the mail came to Down House on June 18, 1858. Darwin got a letter from the other side of the world, from a traveling naturalist named Alfred Russel Wallace. Wallace was exploring southeast Asia, collecting animals to pay his way, and looking for evidence of evolution. At 21 he had read Vestiges and was seduced by the idea of nature sweeping upward over time. After reading Darwin’s tales of his voyages, Wallace decided he would travel as well.

His first journey was to the Amazon in 1848. Later he traveled to what is now Indonesia to look for orangutans and, he hoped, learn about man’s ancestry. Along his way he financed his trip by sending back boxes of beetles, bird skins, and other specimens to dealers and patrons in London. Darwin was one of those patrons, receiving the skins of birds for his own research, and the two naturalists began to trade letters.

Darwin encouraged Wallace to think broadly and theoretically about evolution, confiding that he had a theory of his own about how species came to be. Wallace decided to write a letter to Darwin to tell him about his own ideas. When Darwin opened it, his heart sank. Wallace had read Malthus as well, and he had also wondered what effect overpopulation would have on nature. And like Darwin, he concluded that it would change species over time and create new ones.

At the time that Darwin received Wallace’s letter, he was planning to write for a few more years before going public. But here was much of his own theory in the handwriting of another scientist. It was not identical–Wallace did not make much of the competition between members of the same species. He proposed simply that the environment culled unfit individuals. But Darwin would not rob Wallace of his proper credit. His sense of honor ran deep, and he would rather have burned his own book than have anyone think he cheated Wallace.

So Darwin arranged with Lyell that the Linnaean Society would hear papers on both his own work and Wallace’s at the same time. On June 30, 1858, the society listened to extracts from Darwin’s 1844 essay, part of a letter he had written about his idea to Hooker in 1857, and Wallace’s paper. Twenty years of cautious research and fretting was suddenly over. The world could now judge.

But no judgment came. Darwin’s and Wallace’s papers were read during a long, rushed session of the Linnaean Society, and were met with silence. Perhaps the papers were too terse, too polite, for the audience to realize just what Darwin and Wallace were proposing. Darwin decided that he now had to lay out his argument in a paper in a scientific journal.

In the months that followed, he struggled to shrink his gargantuan Natural Selection to a brief summary that he could publish. But as he worked on it, the summary swelled to book length again. He simply had too many arguments and pieces of evidence to counter the attacks he knew would come. He contacted John Murray, the publisher of Journal of Researches, and asked if he would print a second book. Journal of Researches had been a hit, so Murray agreed to publish the new volume, which came to be called On the Origin of Species by Means of Natural Selection.

Along the way Darwin’s health came under fresh attack. When he received the first finished copy of his book, bound in royal green cloth, in November 1859, he was recovering at a spa in Yorkshire. Soon the complimentary copies arrived, and Darwin sent one to Wallace in Indonesia. Along with the book he sent a note: “God knows what the public will think.”

“There Is a Grandeur in This View of Life”

The argument that appeared in Origin of Species had evolved from its ancestral form in 1844. Now it had become something far broader–an all‑encompassing explanation for life on Earth.

Darwin chose to start his argument not on the remote Galápagos Islands, not in the murky depths of the oceans among coral reefs, but in ordinary, comfortable English life. He talked about the many forms that animals and plants could assume in the hands of breeders. Pigeon breeders had doubled the normal allotment of feathers on the fantail; they had turned the neck feathers on the Jacobin into a hood. These were the sorts of traits that could set off a bird as a species of its own, and yet the breeders had created them in only a few generations.

Darwin acknowledged that no one really understood how heredity allowed breeders to work these miracles. Breeders simply knew that different traits tended to be inherited with each other. Cats with blue eyes, for instance, are invariably deaf. But while heredity might be a mystery, at least it was clear that parents produced offspring that tended to be like them–although each generation came with a certain amount of variability.

If you came across a fantail and a Jacobin in the wild, you might think they were different species, yet, strangely, they could still mate and produce fledglings. In fact, Darwin pointed out, it is very hard to distinguish between species and varieties in the wild. Biologists argue about whether certain kinds of oak trees belong to the same species. Darwin suggested that the confusion stemmed from the fact that varieties have some of the same characteristics as species. And that is because varieties are often incipient species themselves.

How could an incipient species become a full‑blown one? Here Darwin brought Malthus into the argument. Even a slow‑breeding species like a human or a condor can double its numbers in 20 or 30 years, easily overrunning the planet in a few millennia. But plants and animals are regularly wiped out in staggering numbers. Darwin recalled how four‑fifths of the birds around Down House died one year in a cold snap. The tranquil surface of nature hid a massive slaughter from view.

Some members of a species survived these challenges thanks to luck, while others had certain qualities that made them less likely to die. The survivors would reproduce, while the badly adapted ones would die. Nature, in other words, was a breeder of its own, and a far superior one to humans. A human might breed pigeons for only one trait, such as tail feathers, while nature bred for countless ones–not just traits of flesh and blood, but of instincts as well. “She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life,” Darwin wrote. “Man selects only for his own good; Nature only for that of the being which she tends.”

And whereas breeders can do their work only over the course of years or decades, nature has at its disposal a vast expanse of time. “It may be said that natural selection is daily and hourly scrutinizing, through the world, every variation, even the slightest,” Darwin wrote. “We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages.”

If natural selection worked on a variety long enough, it would turn it into a new species of its own. After a thousand generations, a single species of bird made of two varieties might end up as two distinct species. Just as individuals of a given species struggle with one another, they also struggle with members of other species. And the competition between two similar species would be most intense. Eventually one of them might be driven out of existence. This, Darwin argued, accounted for all of the fossils of animals that could no longer be found on Earth. They had not simply disappeared–they had been obliterated by other animals.

To help his readers understand this process, Darwin drew the one illustration that appeared in his book. At the bottom were a few original species, which rose like limbs on a tree, dividing over time into new branches. Most of these branches were nothing more than twigs–varieties or species that became extinct–but some of them branched their way all the way to the top of the page. Life was not a Great Chain of Being, said Darwin, but a bushy tree.

Origin of Species is a deeply defensive book, written by a man who had quietly listened for years to other scientists scoff at evolution, and had imagined them scoffing at him as well. He addressed their objections one by one. If old species gradually turned into new species, then why were animals so distinct from one another? Darwin’s answer was that competition between two similar species would tend to drive one of them extinct, so that the animals alive today would be only a scattered selection of all the species that had ever lived.

But shouldn’t we be able to see these intermediate forms as fossils? Darwin reminded his readers that fossils, by their nature, could provide only a few fragments of life’s history. In order to become a fossil, a carcass had to be properly buried in sediment, turned to rock, and then avoid destruction by volcanoes or earthquakes or erosion. Those chances are abysmally low, and so a species, which once included millions of individual animals, might be known from a single fossil. Gaps in the fossil record shouldn’t be a surprise–they should be the rule. “The crust of the earth is a vast museum,” Darwin wrote, “but the natural collections have been made only at intervals of time immensely remote.”

How could natural selection create complex organs, or entire bodies, that were made of so many interdependent parts? How, for instance, could it make a bat or an eye? Fossils couldn’t be expected to tell the whole story. Instead, Darwin turned to living animals as analogies to show at least that such a transformation wasn’t impossible. For bats, he pointed to squirrels. Many tree‑living squirrels have four ordinary legs and a slender tail. But there are also some species that have flattened tails and loose skin. Then there are squirrels that have broad flaps stretching between their legs and even their tail and can parachute out of trees. Then, Darwin pointed out, there are gliding mammals known as flying lemurs, which have elongated fingers and a membrane that stretches from jaw to tail.

Here was a relatively smooth gradation from an ordinary four‑legged mammal to a creature with almost a batlike anatomy. It was possible that the ancestors of bats went through this evolutionary sequence and then went one step farther, evolving the muscles necessary for true flight.

Likewise, there was no need for an eye to pop out of an animal’s head all at once. Invertebrates such as flatworms have nothing more than nerves with endings coated in light‑sensitive pigments. Some crustaceans have eyes that consist of little more than a layer of pigment coated by a membrane. Over time, this membrane could separate from the pigment and begin to act like a crude lens. With small alterations, such an eye could turn into the precise telescopes that birds and mammals use. Because a little eyesight is better than none at all, each new step along the way would be rewarded by natural selection.

With his discovery of natural selection, Darwin turned back to the ideas of other scientists and showed how they made more sense as parts of his own theory. As a young man Darwin had admired Paley, but now he showed how natural designs could come into being without a designer’s direct control. Karl von Baer had demonstrated how embryos of different animals resembled one another early on and grew more particular. For Darwin, this was a sign of the common heritage of animals, and the differences in their development came after their ancestors had diverged.

And Darwin even absorbed Owen’s archetype. “I look at Owen’s Archetypes as more than ideal, as real representation as far as the most consummate skill & loftiest generalization can represent the parent of the Vertebrata,” he once wrote to a colleague. To Owen, the homology between a bat wing and a manatee paddle showed how the mind of God worked. But to Darwin, the homology was a sign of inheritance.

Darwin gingerly avoided writing much of anything about what his theory meant for humanity. “In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.”

He was not going to make the mistake Robert Chambers had made in Vestiges. He had an argument to make, and he didn’t want emotions to interfere. But Darwin did make some attempt to stave off the despair people might feel. “Thus,” he wrote in the final lines of his book, “from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely the production of the higher animals, directly follows. There is a grandeur in this view of life, with its several powers, having been originally breathed 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.”

Ape Versus Bishop

That winter, as blizzards buried England, thousands of people kept warm by the fire and read Darwin’s book. The first printing of 1,250 copies was snapped up in a day, and in January 3,000 more were printed. Huxley sent Darwin words of praise but warned him of the battle to come. “I am sharpening up my claws and beak in readiness,” he promised. Newspapers generally offered only brief articles about it, but the reviews, where the literary world debated the great ideas of the nineteenth century, went into more depth. Huxley and other allies of Darwin praised it, but many reviews saw it as blasphemy. The Quarterly Review declared that Darwin’s theory “contradicted the revealed relation of the creation to its Creator” and was “inconsistent with the fullness of His Glory.”

The review that made Darwin angriest appeared in the Edinburgh Review in April 1860. It was anonymous, but anyone familiar with Richard Owen knew he had written it. It was stunning in its animosity. Owen called Darwin’s book “an abuse of science.” He complained that Darwin and his disciples pretended that natural selection was the only possible natural creative law. Owen wasn’t actually opposed to evolution; he just didn’t like what he considered blind materialism.

Yet Darwin had done what Owen couldn’t. Owen had tried to synthesize the discoveries of biology, but he had ended up with murky notions of archetypes and continuous creation. Darwin, on the other hand, could account for the similarities between species with a mechanism that was at work in every living generation.

Owen wrote his review out of anger, both at Darwin and at Huxley. Huxley had been attacking Owen in public lectures with a venom that shocked him. Huxley despised Owen both for the way he curried favor with aristocrats and for what he considered shoddy science. He mocked Owen’s theory of continuous creation as absurd. Owen became so angry with his taunts that during one of his public lectures he glared at Huxley, declaring that anyone who didn’t see the fossil record as a progressive expression of divine intelligence must have “some, perhaps congenital, defect of the mind.”

Their fiercest fights broke out in the years just before Origin of Species was published, as Owen tried to prove that humans were distinct from other animals. During the 1850s, orangutans, chimpanzees, and gorillas were beginning to emerge from their jungle obscurity, and Owen dissected their bodies and studied their skeletons. He worked hard to try to find some mark that distinguished humans from them. If we were nothing but a variation on an ape, then what became of morality?

What made humans most distinct from animals, Owen assumed, was our mental capacity: our ability to speak and reason. Owen therefore looked in the brains of apes to discover the anatomy that marked that difference. In 1857 he claimed to have found a key distinction: unlike the brains of apes, the cerebral hemispheres of the human brain extended so far back that they formed a third lobe, with a structure Owen called the hippocampus minor. He declared that its uniqueness warranted putting humans in a subclass of their own. Our brain was as different from a chimp’s as a chimp’s was from a platypus’s.

Huxley suspected that Owen had been misled by studying badly preserved brains. His elaborate classifications were built on a fundamental error. (Huxley liked to say that they stood like “a Corinthian portico in cow dung.”) In fact, Huxley argued, the human brain was no more different from a gorilla’s than a gorilla’s was from a baboon’s. “It is not I who seek to base Man’s dignity upon his great toe, or insinuate that we are lost if an Ape has a hippocampus minor,” Huxley wrote. “On the contrary, I have done my best to sweep away this vanity.”

Owen’s furious review of Darwin’s Origin of Species raised the tension between him and Huxley even higher, and finally, a few months later, in June 1860, their hostility exploded. The British Association for the Advancement of Science held its annual meeting at Oxford, attended by thousands of people. Owen, the association’s president, gave a talk on June 28, explaining once again how the human brain was distinct from that of apes. Huxley had an ambush planned. At the end of the talk, Huxley stood and announced that he had just received a letter from a Scottish anatomist who had dissected a fresh chimpanzee brain. The anatomist had discovered that it looked remarkably like a human brain, complete with a hippocampus minor. With a packed audience looking on, Owen had no way to defend himself. Huxley could not have chosen a more public place to humiliate him.

Having won the battle of the brains, Huxley decided to leave the Oxford meeting the next day. But then he bumped into Robert Chambers, the still anonymous author of Vestiges. Chambers was horrified to hear that Huxley was going to depart. Didn’t he know what the next day had in store?

Rumors were racing through Oxford that Bishop Samuel Wilberforce was going to attack Darwin. For years, Wilberforce had been a leading religious voice against evolution. He had attacked Vestiges in 1844, calling it foul speculation, and now the bishop saw Darwin’s book as no different. An American scientist named John William Draper was scheduled to give a talk the next day about “Darwinism” and its implications for society. Wilberforce was going to use the opportunity to denounce Darwin in public, at Britain’s most important scientific meeting. Owen was staying at Wilberforce’s home during the meeting, and no doubt he was coaching the bishop. Chambers convinced Huxley to stay on for Draper’s talk and defend Darwin.

Owen opened the conference the following day. Upward of a thousand people packed the auditorium, and to them he announced, “Let us ever apply ourselves seriously to the task of scientific inquiry, feeling assured that the more we thus exercise, and by exercising improve, our intellectual faculties, the more worthy shall we be, the better shall we be fitted to come nearer to our God.”

Draper’s talk was entitled “On the Intellectual Development of Europe, Considered with Reference to the Views of Mr. Darwin and Others, That the Progression of Organisms Is Determined by Law.” By all accounts it was dull, long, and poorly reasoned. Joseph Hooker was in the audience and described Draper’s talk as “flatulent stuff.” The hall grew warm, but as woozy as the audience became, no one left. They wanted to hear the bishop.

When Draper was done, Wilberforce stood and spoke. He had recently written a review of Darwin’s book, and he essentially repackaged it as a speech. He didn’t pretend the Bible should be a test of science, but in his review he had written, “This does not make it the less important to point out on scientific grounds scientific errors, when those errors tend to limit God’s glory in creation.”

Darwin had made such an error. His book was based on wild assumptions and hardly any evidence. His entire argument hinged on this new idea of natural selection. And yet, Wilberforce wrote, “Has any one such instance ever been discovered? We fearlessly assert not one.”

Instead, Wilberforce argued for a loose mix of Paley and Owen. “All creation is the transcript in matter of ideas eternally existing in the mind of the Most High–that order in the utmost perfectness of its relation pervades His works, because it exists as in its centre and highest found‑head in Him the Lord of All.”

When Wilberforce ended his speech, he looked to Huxley. He asked him, half‑jokingly, whether it was on his grandfather’s or grandmother’s side that he descended from an ape.

Later Huxley would tell Darwin and others that at that moment he turned to a friend seated next to him, struck his hand to his knee, and said, “The Lord hath delivered him into mine hands.” He stood and lashed back at Wilberforce. He declared that nothing that the bishop had said was at all new, except his question about Huxley’s ancestry. “If then, said I, the question is put to me would I rather have a miserable ape for a grandfather or a man highly endowed by nature and possessed of great means and influence and yet who employs these faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion I unhesitatingly affirm my preference for the ape.”

The audience broke out in laughter, until a man whom Hooker described as “a gray‑haired Roman‑nosed elderly gentleman” stood in the center of the audience, quaking in rage. It was Captain FitzRoy.

FitzRoy and Darwin had grown cool to each other over the years. The captain thought that Darwin’s book about the Beagle’ s voyage was self‑serving and ignored all the help Darwin had gotten from FitzRoy and his crew. Although FitzRoy had dabbled in Lyell’s ancient geology, he had returned to a strict reading of the Bible. In his own book about the voyage, FitzRoy tried to account for all that he and Darwin had encountered with Noah’s Flood. He had been appalled to watch Darwin move even further into heresy, not only abandoning the Flood, but even God’s work.

The captain had come to Oxford to give a talk about storms, and he happened to get wind of the talk by Draper. After Huxley finished, FitzRoy stood and spoke of how he had been dismayed that Darwin entertained views that contradicted the Bible. He declared that reading Origin of Species had brought him “acutest pain.” He lifted up both his arms over his head, a Bible clutched in his hands, and asked the audience to believe in God, not man. Whereupon the crowd shouted him down.

Finally it was Joseph Hooker’s turn. He climbed to the podium to attack Wilberforce. Later he wrote to Darwin about his speech. “I proceeded to demonstrate that 1) he could never have read your book, 2) he was absolutely ignorant of the rudiments of Botanical Science and the meeting was dissolved forthwith, leaving you master of the field.”

If Darwin was master of the field, he was a missing master. Practically a recluse now at age 50, he stayed away from the Oxford meeting. As Hooker and Huxley defended him, he was spending a few weeks in the village of Richmond, where he was being treated yet again for his chronic illness. There he read the letters of his friends, describing their speeches, with an ailing awe. “I would have soon have died as tried to answer the Bishop in such an assembly,” he wrote to Hooker.

The Oxford meeting quickly became a legend, and as with all legends, what really happened receded behind a fog bank of embellishment. Each of the players in the drama offered his own version, in which he came off best. Wilberforce was convinced that he had won the debate, while Huxley and Hooker each thought they had delivered the fatal blow to the bishop. To this day, it’s not clear what happened, and Darwin himself had a hard time figuring out what took place that warm day in June. Only one thing was certain to him: his 20 years of hiding were over.

In Darwin’s own lifetime, he would become recognized as one of the great masters of science. By the 1870s, almost all serious scientists in Britain had accepted evolution, although they might argue with Darwin about how it unfolded. His statue stands at the Natural History Museum in London, and he lays buried in Westminster Abbey, close by Newton’s grave.

But the great irony of Origin of Species is that only in the twentieth century would its true power be recognized. Only then did paleontologists and geologists work out the chronology of life on Earth. Only then did biologists uncover the molecules that underlie heredity and natural selection. And only then did they begin to truly comprehend how powerfully evolution shapes everything on Earth, from a cold virus to the human brain.

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