Darwin Charles

Charles Darwin was born in 1809 at Shrewsbury, England. He was expected to follow in the footsteps of his father and grandfather, who were both prosperous physicians. (His grandfather, Erasmus, in addition to being a doctor, was also a famous philosopher, poet, and naturalist, and the first in Europe to publish a theory of evolution.) Charles was sent to study medicine at Edinburgh at the age of sixteen, but he was squeamish about the sight of blood and could not bear the screams of a strapped-down child in surgery. He soon rejected the pursuit of a career in medicine. To his father's disgust, Charles's only real interests seemed to be collecting beetles, shooting birds, and poking at rocks and plants—activities suitable only for an idle squire or a country parson. Doctor Darwin urged his son to become a clergyman instead and sent him to Christ's College, Cambridge, to prepare for a career as a country vicar.

Darwin was befriended by one of his Cambridge professors, the clergyman-botanist John Henslow, who instructed him in natural history. When Darwin was twenty-two, Henslow recommended him to a ship's captain, Robert FitzRoy, who was seeking a ship's naturalist and gentleman companion for a voyage around the world. FitzRoy (who was then only twenty-four years old himself) was taking the surveying ship HMS Beagle to chart the coast of South America, and then to explore the islands of the Pacific, Tasmania, Australia, and South Africa. Henslow expected that Charles would "snap at the opportunity." However, Charles's father proclaimed it a dangerous, hare-brained scheme that no "man of sense" would approve. He soon relented, however, and Charles abruptly quit his ecclesiastical studies to spend the years from 1831 to 1835 voyaging on the Beagle.

Darwin was thus able to explore the rain forests of South America, and he visited Australia, Tahiti, and South Africa, where he observed and collected thousands of plant and animal specimens. In Patagonia, he chipped a fossilized giant sloth from a cliff; and in the South Seas he discovered how coral islands and reefs were formed. It was a combination of adventure, hardship, scientific discovery, and unremitting hard work, all packed into five years. He galloped on horseback alongside Argentine gauchos, rode rough seas, survived killer storms and earthquakes, and wandered awestruck through creeper-laced rain forests teeming with gaudy birds and exquisite orchids. He habitually sought underlying connections and regularities, and eventually realized that the key was the shared history of life forms adapting to a changing earth.

After returning home, Darwin married his cousin Emma Wedgwood and settled down to family life near the village of Down, in Kent,

Portrait of Charles Darwin (Library of Congress)

some sixteen miles south of London. His first two books, Journal of Researches aboard the H.M.S. Beagle (1839) and "The Structure and Distribution of Coral Reefs" (1842), established him as a rising young scientist of talent and also as a popular author.

For forty years, the Darwins and their children (they had ten, of which seven survived) lived in a spacious old house, complete with gardens, fields, a patch of woods, greenhouse, later a clay tennis court, and about fifteen servants. Darwin became a reclusive semi-invalid, devoted to writing, reading, and conducting experiments in his garden and greenhouse. A casual visitor would never have guessed that from this sleepy, idyllic retreat he was shaking the world.

Darwin had been strong and vigorous during the Beagle voyage, but he suffered ill health from a mysterious malady during most of his life thereafter. (Some scholars believe he was infected by a blood parasite from a beetle's bite in Argentina, giving him chronic Chagas's disease, coupled with debilitating anxiety from long-standing neurosis.)

Around 1837, Darwin began keeping notes on "the species question" in an ambitious attempt to discover "the laws of life." Building on the theories of his grandfather Erasmus (1731-1802), he became a "transmutationist" or evolutionist. (He used the terms transmutation or the development hypothesis. The term evolution was coined by philosopher Herbert Spencer and did not appear in Darwin's Origin of Species until the fifth edition, in 1869.)

Erasmus had believed that all living things arose by descent with modification from common ancestors over immense periods of time. During the early 1840s, he discovered a mechanism for evolution, which he called "natural selection." Organisms vary in nature, and those best adapted would survive and produce more offspring like themselves. But before he could publish his big "species" book, a younger naturalist, Alfred Russell Wallace, working alone in the jungles of Malaysia, came up with exactly the same theory and sent it to Darwin. There was an initial period of panic at being "scooped," after which Wallace's and Darwin's papers on natural selection were jointly presented at a meeting of the Linnean Society of London on July 1, 1858.

Although the Darwin-Wallace theory can be summarized in a few pages, how to use it to unravel nature's mysteries fills Darwin's 17 scientific books and more than 150 articles— an output that founded the modern research tradition. This incredibly productive life's work revolutionized every field he touched: botany, paleontology, physiology, taxonomy, comparative psychology, zoology, what we now call ecology, primatology, genetics, pale-oanthropology, sociobiology, and all of the life sciences.

Current scientific theories of biodiversity, ecology, and evolution spring directly from the writings of Charles Darwin and his junior partner Alfred Russell Wallace, who independently discovered the theory of evolution by means of natural selection. Darwin's masterpiece, On the Origin of Species (1859), established the theory in science. Although Darwin's fieldwork predated Wallace's by more than twenty years, both had been impressed and influenced by the riotous diversity of plant and animal species they found in the Brazilian rain forests.

Divergence from common ancestors leads to biodiversity. Evolution is often pictured as a family tree or branching bush, bristling with divergent forks and twigs. Each lineage repeatedly splits and differentiates, and lines splay out, in Alfred Russel Wallace's image, "like the twigs of a gnarled oak or the vascular system of the human body." Some of Darwin's disciples, like German zoologist Ernst Haeckel, spent years working out detailed "trees of life," showing the divergence of families, genera, and species over time

Although today they may seem like inseparable concepts, evolution and divergence have not always been associated. Darwin sketched such a tree in an early notebook, but the principle of divergence occurred to him much later—about fifteen years after he had developed his basic theory of natural selection. Divergence was a crucial missing piece even during the writing of the Origin, and yet Darwin referred to its last-minute inclusion as "the keystone" of his book.

In the later views of both Darwin and Wallace, divergence serves a double function in evolution. First, it enables a given species under selection pressure to survive in modified form by exploiting new niches in the ecology. And second, the gain in diversity boosts the habitat's carrying capacity, enabling it to support a greater total amount of life. Typically, small, isolated habitats (such as Darwin's beloved Galapagos Islands, in the Pacific Ocean west of Ecuador) exhibit a startling diversity of closely related species, adapted for exploiting different foods or parts of the habitat.

Wallace's significant 1855 paper (the "Sarawak Law") began with this question: If one examines the numbers of closely related species within genera, geographic distribution of natural groups, and kinds of differences between species in a local area, what overall pattern (he called it a "law") would emerge? His answer was that the largest number of species seemed to be produced from those genera confined to a small area (such as islands), and their differences were related to feeding adaptations (sharp beaks, blunt beaks, long beaks, and so forth).

When Darwin read this paper, he scrawled on it: "Why should this law hold?" The answer, he later realized, was that under selective pres sures, organisms evolve to fill "vacant places in the natural economy." He compared it to a division of labor, with efficient specialists exploiting the various food sources in a limited area. To test the theory in his own garden, he stripped the ground of turf in a square 3 by 3 feet and carefully monitored how many species would fill in the bare little plot. He was astonished when, after only a few weeks, he counted fifty-three varieties and species that had sprung up in his test square.

What is now taken for granted was then a startling insight: contrary to "common sense" expectations, the fierce struggle for existence does not reduce the overall number of related species in an area of limited resources. Instead, it has the paradoxical effect of allowing many more species and individuals to thrive there.

More than a century later, David Tillman, of the University of Minnesota, followed up on Darwin's experiments with biodiversity. Till-man directed a team of fifty workers to burn, plow, plant by hand, and tend 147 plots of grassland in the Minnesota prairie, each measuring about 100 square feet. In a few weeks, between one and twenty-one native species appeared in each plot. Those with more species, he found, retained nitrogen—the plant's most crucial nutrient—much more efficiently. Like Darwin, Tillman was struck by the fact that closely related species would tend to exploit slightly different resources in the same habitat, and that the resultant diversity would be beneficial to all (Tilman and Downing, 1994; Tilman et al. 1996).

The concept of diversity is related to Darwin's ecological view of nature, although the term ecology was not coined until 1869 by Ernst Haeckel, who was inspired by a passage from the Origin of Species. Darwin had marveled at a common riverbank "clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us."

This "tangled bank" expresses Darwin's view of nature as a web of interrelationships binding various plants and animals into a community. Not only is the visible vegetation entangled; the lives of different species are also intertwined. Ecological interdependence was one hallmark of Darwin's contribution to modern thought. He saw evolution as a lateral rather than simply an onward movement, whose power lies in multiple relationships as much as in selecting out.

When he first met the English zoologist Thomas Huxley, later to become his great friend and champion, Darwin was examining a tray of specimens at the British Museum. Huxley said something about what clear boundaries there are between natural groups. Glancing up, Darwin quietly replied, "Such is not altogether my view." Huxley later recalled that "the humorous smile which accompanied his gentle answer . . . long haunted and puzzled me." In the popular perception, Darwin is remembered best as a solitary observer and field naturalist. Actually, he excelled at two other modes of research for which he is not generally credited: collaboration and experimentation. He experimented constantly in his greenhouse and garden. To test whether certain plants that had evolved on continents could be the same ones found on distant islands, he soaked seeds for months in barrels of brine, then planted them to see which could survive long immersion in salt water. He measured the activity of earthworms in his garden by calibrating the rate at which a heavy stone sank into the turf.

Over the years, Darwin's books tackled the implications of his theory for human origins

(The Descent of Man, 1871), behavioral evolution (Expression of the Emotions in Man and Animals, 1872), coevolution of insects and plants (The Varying Contrivances by which Orchids Are Fertilised . . ., 1862), domestic breeding (Variation in Domesticated Plants and Animals, 1868), and botany and plant physiology (Movements and Habits of Climbing Plants, 1865; Insectivorous Plants, 1875; Different Forms of Flowers on the Same Plant, 1877). His first (Structure and Distribution of Coral Reefs, 1842) and last (Formation of Vegetable Mould through the Action of Worms, 1881) books were demonstrations of how great geological features may result from small, slow causes, acting regularly, over immense periods of time. It is remarkable that despite "never knowing a day of robust health" for forty years, Charles Darwin managed to write his 17 scientific books and 155 articles—a lifetime output of more than 10,000 published pages—working no more than two or three hours a day. "I have always maintained," he said, "it is dogged as does it."

When he died of cardiac disease in 1882, he expected to be buried in the local churchyard at Downe Village, but his powerful scientific friends petitioned for burial in Westminster Abbey, England's highest honor. His final resting place is a few paces away from that of Sir Isaac Newton, another scientific immortal.

Eulogizing his old friend, Thomas Henry Huxley said, "None have fought better, and none have been more fortunate than Charles Darwin. He found a great truth, trodden underfoot, reviled by bigots, and ridiculed by all the world; he lived long enough to see it, chiefly by his own efforts, irrefragably established in science, inseparably incorporated with the common thoughts of men. . . . What shall a man desire more than this?" (Huxley, 1893).

—Richard Milner

See also: Coral Reefs; Evolution; Evolutionary Biodiversity; Galapagos Islands and Darwin's Finches;

Mass Extinction; Natural Selection; Wallace, Alfred Russel

Bibliography

Browne, Janet. 1995. Charles Darwin: Voyaging, Volume I of a Biography. New York: Knopf; Colp, Ralph. 1977. To Be an Invalid: The Illness of Charles Darwin. Chicago: University of Chicago Press; Desmond, Adrian, and James R. Moore. 1991. Darwin: A Tormented Evolutionist. New York: Warner; Huxley, Thomas Henry. 1893. Collected Essays of Thomas Henry Huxley. Vol. 2 ("Darwiniana"). London: Macmillan. p. 247; Keynes, Randal H. 2002. Charles Darwin, His Daughter, and Human Evolution. New York: Riverhead, Penguin Putnam; Mayr, Ernst. 1991. One Long Argument: Charles Darwin and the Genesis of Modern Evolutionary Thought. Cambridge: Harvard University Press; Moorehead, Alan, 1969. Darwin and the Beagle. New York: Harper and Row; Sher-mer, Michael. 2002. In Darwin's Shadow: The Life and Science of Alfred Russel Wallace. New York: Oxford University Press; Tilman, D. and J. Dowling. 1994. "Biodiversity and Stability in Grasslands." Nature 367:363-365; Tilman, D., D. Wedin, and J. Rnops. 1996. "Productivity and Sustainability Influenced by Biodiversity in Grasslands Ecosystems." Nature 379: 718-720.

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