The Descent of Man: The Concise Edition

In 1871 Charles Darwin published The Descent of Man, in which he laid out for the first time his argument that humans were products of evolution. The Descent of Man: The Concise Edition introduces a new generation of readers to this scientific masterpiece, with excerpts from the original text, each covering Darwin’s major themes. Each selection is accompanied by an introductory essay by Carl Zimmer, reflecting on the history of Darwin’s ideas about humans, and what twenty-first century science has to say about them. With a foreword from noted primatologist Frans de Waal.


From the introductory essay…

The history of science is rife with fateful meetings. The astronomer Tycho Brahe hires a young assistant named Johannes Kepler, who will go on to discover in Brahe’s observations the law of planetary motion. A bright but aimless British physicist named Francis Crick is introduced to a boisterous young American biologist named James Watson. The two soon discover they share a curiosity about a strange molecule called DNA. And on a warm afternoon in the early spring of 1838, the young Charles Darwin climbed into an orangutan’s cage.

The sight of a living ape was a new sensation in England. Before the 1830s, Europeans only knew of apes through vague accounts from travelers returning from Africa and Indonesia. Beginning in 1835, however, chimpanzees and orangutans began to appear at London’s Zoological Gardens. Face to face, the apes inspired uneasy fascination. Queen Victoria declared them “frightful, and painfully and disagreeably human.”

The first ape to come to London, a chimpanzee named Tommy, was put in a sailor’s suit. The second, a female orangutan named Jenny, was put in a dress. Both were taught to eat with spoons. Yet the humanlike qualities of these apes did not cause most observers to question the uniqueness of humans. An article about Jenny’s humanlike behavior stressed that ‘in nothing does it trench upon the moral or mental provinces of man.’ After all, it was agreed, God had separately created man and orangutan and every other species on Earth in its current form. He had endowed each species with its own combinations of traits, all of which displayed his handiwork. One need only look at the complex barbs of a feather or the muscles of the human hand to see the work of a Creator. An orangutan’s ability to eat with a spoon was just a distraction from that great truth.

A few people, however, harbored some doubts. Charles Darwin was one of them. In 1838, those doubts had not yet flowered into a full-blown theory of life. Darwin was only 29 at the time, and would not publish his first account of evolution for another 21 years. But his doubts were already deep enough to lure him into Jenny’s cage.

Historians have long wondered how the seeds of evolution were planted in Darwin’s mind. They were probably already there in his youth, where they remained dormant for years. His grandfather, the physician Erasmus Darwin, wrote a long poem called Zoonomia in the 1790s, in which he argued that life had changed over vast stretches of time, with new kinds of creatures emerging from old ones. This transformation would later become known as evolution. Charles Darwin learned more about evolution as a teenager, when he traveled to Edinburgh to study medicine. Surgery and autopsies appalled him. His fondness for nature was already becoming plain, as he explored tidal pools instead of sitting through lectures. Darwin soon found a mentor in the Scottish naturalist Robert Grant. Grant taught Darwin not only about natural history, but about evolution as well. Grant had been deeply influenced by Darwin’s grandfather, as well as by the more recent work of the French naturalist, Jean Lamarck.

Lamarck argued that two laws of nature gradually changed life over time. Simple life forms perpetually came into existence, and they were all driven towards greater degrees of perfection. Species also adapted to their particular environments through experience. Giraffes stretching to reach leaves, Lamarck suggested, might acquire longer necks. The giraffes could then pass down their longer necks to their offspring, Lamarck believed.

While Grant and a few other naturalists embraced Lamarck, most scholars viewed him with scorn. Lamarck was challenging a fundamental tenet of Christianity, and he even dared to suggest that human beings were also the product of evolution. Lamarck speculated how an ape much like orangutans or chimpanzees might gradually stand upright and begin to speak, and thus become human.

Despite the influence of his grandfather and Grant, Darwin doesn’t appear to have taken evolution seriously as a young man. Rejecting medicine, he began preparing to join the clergy. At the University of Cambridge he read the influential 1802 book Natural Theology by the Reverend William Paley. Paley asked his readers to imagine walking across a heath and coming across a watch. By its sheer complexity, his readers would know someone had made it. Paley argued that eyes and feet and other traits showed similar signs of design. Darwin admired Paley’s rhetoric, although he was not a terribly serious student of theology. In his free time, Darwin hunted for beetles in the countryside.

In 1831, as Darwin was finishing up at Cambridge, he received a rare invitation. Robert Fitzroy, the captain of HMS Beagle, was searching for a well-educated gentleman to join him on a voyage around the Earth. Darwin accepted, and became the Beagle’s unofficial naturalist. The voyage latest five years, during which time Darwin explored Amazon jungles, climbed the Andes, and prowled Pacific islands few Europeans had ever seen. He gathered much of the raw material that he would later use to develop his own theory of evolution.

But Darwin was not yet an evolutionist. On the voyage of the Beagle he simply made observations’of mountains, of coral reefs, of giant tortoises’and sought natural explanations for how they came to be. One of his best guides was a newly published book he had brought along on the voyage, called Principles of Geology. The author, a British lawyer-turned-geologist named Charles Lyell, argued that mountains and valleys and other geological features were not the result of Noah’s flood or some other sudden catastrophe. Instead, the surface of the planet was the product of a long series of gradual changes. Rain gradually wore down canyons. Mountains inched up out of the sea. Darwin saw ample evidence on his voyage in support Lyell’s theory of an ancient, slowly changing Earth.

Lyell also discussed evolution in Principles in Geology. He sketched out Lamarck’s arguments, describing how an orangutan supposedly ‘is made slowly to attain the attributes and dignity of man.’ But Lyell rejected Lamarck. He pointed out the recent discovery of ibises mummified for thousands of years in Egypt. If Lamarck were right, one would expect to see a difference between the mummified birds and living members of their species. No such difference had been found. Yet Lyell did not believe that all life was created at Earth’s first dawn. He proposed that new species were separately created over the course of Earth’s history.

This argument did not make sense to Darwin. After his return to England in 1837, he began to carefully describe the fossils, birds, plants, and other specimens he had gathered on his travels. He recorded his ideas in a series of notebooks. The notebooks document is embrace of evolution. Just as geology showed evidence of a slowly changing Earth, living species showed evidence of a slow transformation. How else to explain fossil rodents and anteaters in South America that were giant versions of the mammals that Darwin saw on his visit? Darwin had discovered new species of finches on the remote Galapagos Islands, with beaks so different from one another he had not realized at first that they were finches at all. It was hard to square those finches with the idea of special creation. Perhaps an ancestral finch had given rise to new species, Darwin thought, each with its own adaptations.

In his notebooks, Darwin sketched a tree, each branch a species, joined in kinship with other species. Above the tree he wrote, “I think.”

Humans, Darwin immediately recognized, might also belong on one of those branches. Hence his fascination with Jenny. In the similarities between orangutans and humans Darwin saw signs of kinship, of a shared ancestry. On March 28, 1838, Darwin rode to the London zoo and paid a visit to Jenny, who was weathering the British climate in the heated giraffe house. As a wealthy guest, Darwin was allowed to enter the cage itself. In a letter he wrote four days later to his sister Susan, he described what he saw:

…the keeper showed her an apple, but would not give it her, whereupon she threw herself on her back, kicked & cried, precisely like a naughty child.–She then looked very sulky & after two or three fits of pashion, the keeper said, “Jenny if you will stop bawling & be a good girl, I will give you the apple.– She certainly understood every word of this, &, though like a child, she had great work to stop whining, she at last succeeded, & then got the apple, with which she jumped into an arm chair & began eating it, with the most contented countenance imaginable.

Darwin watched Jenny gaze at herself in a mirror. She used bits of straw like tools. Her face contorted much as a child would. Others might believe they were vastly different from an orangutan, but Darwin didn’t. He decided that much of that difference was a superficial matter of clothes and manners. His mind raced back to the people he had encountered on his voyage aboard the Beagle. He had met naked Indians in Tierra del Fuego. But he had also met Fuegans who had traveled to England and taken up the customs of western civilization.

“Let man visit Ourang-outang in domestication,” he wrote in his notebook, “hear expressive whine, see its intelligence when spoken [to]; as if it understand every word said’see its affection.’to those it knew.’see its passion & rage, sulkiness, & very actions of despair; let him look at savage, roasting his parent, naked, artless, not improving yet improvable & let him dare to boast of his proud preeminence.”

Darwin kept his notebooks secret. His dangerous thoughts about human origins would stew in his mind for over three decades. He would finally share them with the world 33 years later, with the publication of his 1871 book, The Descent of Man, and Selection in Relation to Sex.

The Descent of Man is one of the most important books in the history of biology, but it is also one of the most baffling. A reader can be forgiven for wondering why the book exists at all. Twelve years earlier, Darwin had introduced the world to his theory of evolution withOn the Origin of Species by Means of Natural Selection. An account of how evolution produced humans would have made a splendid final chapter. And yet Darwin scrupulously avoided almost any mention of humans in the Origin of Species. When Darwin finally did turn his attention to mankind and wrote The Descent of Man, he produced a sprawling book that seems arranged to frustrate any attempt to read it all the way through.

Darwin buries the skeleton of his argument under fleshy folds of esoterica–the length of European shinbones, the habit rabbits have of stamping their feet in fear, lizard snouts, peacock feathers, the Egyptian custom of knocking out their front teeth. In fact, even the title of the book is misleading, because most of The Descent of Man is not in fact about man at all. Darwin dedicates over half of the book exclusively to the courtship of animals.

For all these frustrations, The Descent of Man marks a turning point in the history of science. It represents the first effort to trace the origin of human nature to a biologically realistic account of evolution. Darwin argued that the same natural processes that produced iris petals and scorpion tails also produced humanity’s noblest features, such as language and morality. Of course, like any book, The Descent of Man was the product of its time. It is deeply tinted by the prejudices and assumptions of Victorian England. Its picture of humanity is in some ways disturbingly obsolete. And yet over 130 years later it remains a living document. How many other books from 1871 appear regularly in the footnotes of papers published in the latest issues of scientific journals?

This abridged edition will, I hope, give readers new to The Descent of Man an appreciation of its importance. Each excerpt I have selected represents one of the book’s major themes. To introduce them, I discuss the intellectual background to Darwin’s arguments, and then compare his ideas to the current understanding of human nature. The notion that Jenny the orangutan shared a common ancestor with a Victorian gentleman, for example, was outrageous in 1838, but today the evidence is overwhelming. Darwin made his original case by comparing the anatomy and behavior of humans and apes. Today scientists can compare humans and apes on the molecular level and put Darwin’s hypothesis to the test. If orangutans were kin to humans, you’d expect that their DNA would preserve traces of that kinship. And indeed it does. Human DNA bears distinctive sequences shared only by orangutans, gorillas, chimpanzees, and bonobos. Jenny and Darwin were two cousins in a cage.

Copyright © 2007 by Carl Zimmer