Darwin, Charles

Early Life and Background

Charles Robert Darwin was born on February 12, 1809, in Shrewsbury, England, into a wealthy, distinguished family. His paternal grandfather was Erasmus Darwin, a physician who delved into many subjects, including poetry, and who made one of the early statements in support of transmutation, or the belief that species are changeable and not fixed. His father was Robert Waring Darwin, an equally successful physician, who practiced in Shrewsbury. His mother was Susannah Wedgwood, the daughter of the industrialist potter Josiah Wedgwood.

Charles Darwin's education began at home, largely through the efforts of his older sisters who took the place of his mother when she died prematurely. He was eventually sent to a local day school, and in 1818 he entered Shrewsbury School, one of the great English public schools of the nineteenth century. Though a poor student, Darwin developed a keen interest in natural history at a young age, and spent many of his leisure hours collecting insects and plants.

In 1825 Darwin enrolled at Edinburgh University with the intent of studying medicine. He was unsuccessful in his formal studies and developed a distaste for surgery. Two years later, he gave up his medical aspirations and left Edinburgh for Cambridge University, where he intended to study theology in the hopes that he could lead the respectable life of a country vicar. He failed to perform adequately in his formal studies, however. His one true interest remained in natural history, an interest that was encouraged by the professor of botany at Cambridge, John Stevens Henslow (1796-1861). Darwin became so enamored of this mentor that he came to be known as "the man who walks with Henslow." Another important influence on Darwin at this time was the professor of geology, Adam Sedgwick (1785-1873). Though Sedgwick provided the only formal training in science that Darwin was to receive, it was Henslow who provided directive influence in Darwin's life after he recommended him to the Admiralty, which was preparing a survey expedition to chart the coastline of South America. Darwin was to serve as companion to the captain, Robert FitzRoy, on the H.M.S. Beagle. On occasion he was to serve as ship's naturalist. The five-year voyage of the Beagle, beginning on December 31, 1831, and ending on October 2, 1836, was to prove the pivotal experience in shaping Darwin's subsequent scientific work. Darwin returned to England much altered from his experiences. He had not only matured during the voyage, but also distinguished himself with his superb collections, so much so that he became the center of attention in scientific circles.

Scientific Work, 1831-59

While aboard the H.M.S. Beagle, Darwin was struck by the diversity of life that he encountered and how beautifully adapted it was to diverse environments. As he traveled up and down the eastern coastline of South America he was especially interested in the geographic distribution of plants and animals that appeared to replace each other. More importantly, he was taken by the fact that extinct fossils in the area closely resembled living forms of related species, and that the flora and fauna on oceanic islands bore a striking similarity to the nearest continental landmass. He became particularly interested in the distribution of the flora and fauna of a string of recently formed volcanic islands known as the Galapagos, after the unique species of tortoises that are found there. Darwin noticed that each island in the group had an entirely unique flora and fauna. He also noticed that the species bore a striking resemblance to the species on the nearest continental landmass, the western part of South America. With insights from British geologist Sir Charles Lyell (1797-1875), who espoused a uniformitarian rather than a catastrophist geological theory, the weight of this geographic evidence suggested to Darwin that species had not been independently created. They had instead slowly diverged from preexisting species as they came to colonize new habitats and as they adapted to new ecological niches.

Although Darwin had recognized this geographic pattern, he did not have an explanation or a mechanism for how the flora and fauna were able to adapt themselves to their respective environments. The mechanism of evolution occurred to him only after his return to England and after he had been able to sort through his collections. The decisive moment came two years after his return while he was reading English economist Thomas Malthus's An Essay on the Principle of Population (1798). In this famous essay, Malthus had noticed that human populations, if left unchecked, had the tendency to double each generation. In other words, their pattern of growth was exponential. But Malthus also noted that resources necessary to sustain populations increased at a much slower rate, or arithmetically. To Malthus, this meant one thing: that at some point members of the population were subjected to strong competition for those resources, and that such events as war, disease, and famine were natural ways to keep the population in step with available resources. Darwin realized that this principle could just as easily apply to populations of animals and plants. In the competitive struggle for existence, Darwin added, those individuals who bore favorable characteristics would be more likely to survive to reproduce. They in turn were more likely to transmit these favorable characteristics to their offspring. Given enough time, subsequent generations of their offspring would depart from the parental types. Given more time, Darwin added, they would diverge even further from their ancestral types, eventually leading to new species. This principle of divergence strengthened and supported what Darwin called his theory of descent with modification by the mechanism of natural selection. It is what accounted for the origin of species.

Although he had formulated his theory between 1837 and 1838—now recognized as the critical period for Darwin's intellectual development— Darwin did not set these ideas formally on paper until 1842 in a rough sketch, and in 1844 in what is called his historical essay. He showed this short manuscript only to his close friend, the young botanist Joseph Dalton Hooker (1817-1911). Instead of publishing his theory, Darwin continued his research into the late 1850s, hoping to collect enough evidence to support what he knew to be a very controversial theory. Between 1837 and 1859 Darwin therefore engaged in a number of research projects intended to lend support to his theory, including some botanical studies to understand adaptation.

After formulating his theory, Darwin's plan was to collect data carefully from workers around the world to fortify his theory. In particular he was interested in both plant and animal breeding practices, which had been created by artificial selection, a form of selection through human intervention. He became especially interested in pigeon breeding, a popular hobby for Victorians, because it clearly demonstrated the stunning range of variation possible through artificial selection.

In 1839 Darwin married his first cousin, Emma Wedgwood, and in 1842 the couple left London to settle in the nearby village of Downe. There Darwin could escape from the bustle of the city and devote himself fully to his research. The quiet country environment removed from society was also important to Darwin, who began to suffer from an unknown illness, which sometimes left him incapacitated. Only a select group of scientists had access to him. By the 1850s, the inner circle of Darwin's friends, in addition to Hooker and Lyell, included a young morphologist, Thomas Henry Huxley (1825-1895), who became Darwin's intellectual defender.

Publication of On the Origin of Species

Darwin's peaceful existence was shattered in 1858 when he received a letter from a young naturalist named Alfred Russel Wallace (1823-1913). Wallace had been exploring the Malay Archipelago in Southeast Asia. Darwin faced the contents of the letter with mixed feelings: Wallace had reproduced much of Darwin's secret theory, leaving Darwin to face a possible priority dispute. At the advice of the inner circle, Darwin and Wallace published their work jointly in the Journal of the Linnaean Society in 1858. Darwin used the push from Wallace to complete a longer account of his theory, and included evidence he had gathered not only from his own observations and experiments, but also from his correspondence with naturalists and breeders from around the world. Darwin intended this work to be merely an abstract of his longer theory, but the published book was over four hundred pages. Its full title in the first 1859 edition was On the Origin of Species or the Preservation of Favored Races in the Struggle for Life. The book appeared in bookstores on November 24, 1859, and promptly sold out on the first day. It was to go through six editions.

Darwin's life was permanently changed as the theory that Huxley named "evolution" became a topic of heated debate. It was criticized on the scientific front because it failed to provide an adequate theory of heredity and because blending theories of heredity, popular at the time, would have led to a dilution of favorable characteristics. This problem was addressed only after Darwin's death by the rediscovery of Gregor Mendel and his theory of heredity in 1900. Another problem was the age of Earth, which was thought to be about four hundred million years old, an insufficient amount of time to account for the slow, gradual process that Darwin envisioned. This problem was solved after the discovery of radioactivity in the late nineteenth century that, when included in calculations, increased the age of Earth to nearly five billion years, an estimate of time long enough to account for evolution. Yet another difficulty was the fact that Darwin had no direct proof for a process that took place over a long stretch of time. Darwin knew this, and predicted that it would take some fifty years to accumulate enough evidence to support this theory. This was in fact provided beginning in 1920s with the example of industrial melanism in the peppered moth, Biston betularia.

More difficult to resolve were the theological and philosophical questions that followed from the mechanism of natural selection. Even though Darwin had only one line on human evolution in the book, the theory implied that humans were subject to the same mechanistic process as plants and animals. Mechanistic and materialistic, natural selection also challenged the argument for God's existence from design and led to a non-purposive view of the world. To some, like the poet Alfred, Lord Tennyson, a competitive nonpurposive view of nature implied that it was "red in tooth and claw."

Despite a storm of controversy over the mechanism, the fact of evolution was rapidly accepted by scientists. Only after the mechanism of heredity was understood and only after the science of genetics was integrated with natural history was the debate over the mechanism of natural selection extinguished. This did not take place until the interval of time between 1920 and 1950 and was part of the event called the evolutionary synthesis.

Botanical Work

From the start, plants figured prominently in the development of Darwin's ideas of evolution by means of natural selection. Examples from the plant world abound in On the Origin of Species and Variation of Plants and Animals Under Domestication (1868). Not only were plants easily studied and bred, but they showed a stunning assortment of adaptive features. They were to prove one of Darwin's favorite objects of study, becoming the basis of no less than seven books, most of which appeared in the latter part of Darwin's life.

Darwin's first book on plant evolution was titled Fertilization in Orchids (1862). He chose to study orchids because of the range of adaptations they displayed with respect to fertilization. Darwin recognized that these elaborate adaptations served to facilitate cross-pollination by insects such as bees. For this reason, cross-pollinated plants had flowers with bright colors and fragrant nectaries to attract bees and other insects, while wind-pollinated plants, which did not have to attract insect pollinators, had flowers with little or no color.

Darwin also observed that plants that seemed to have one or few flowers had the tendency to be hermaphrodites, having flowers of both sexes on the same plant. Bigger trees with a large number of small flowers, however, usually had flowers of only one sex. To Darwin, this implied that flowers had adapted mechanisms to ensure cross-pollination. This likely increased the variability, and also increased the vigor of the offspring. Darwin performed numerous experiments to understand the manner in which cross-pollination took place in plants and to understand the adaptive function of increased variability. In the process he noted the phenomenon of heterosis, or hybrid vigor, in the progeny of cross-pollinated plants. He also began to unravel the adaptive functions of sexual reproduction.

Darwin's work in pollination mechanisms appeared in two books. The first was Effects of Cross and Self Fertilization (1876), which was followed by Different Forms of Flowers on Plants of the Same Species (1877).

Darwin was also interested in the adaptive functions of climbing plants. He found that the phenomenon of twining, or the differential bending of plants in a clockwise or counterclockwise manner around an object, permitted young or weak plants to raise themselves higher up off the ground. This maximized exposure to air and sunlight in a relatively short time, and without the costly and time-consuming investment of woody supportive structures. The various means used by plants to climb were explored in his book Climbing Plants (1875). The mechanisms by which this and other plant movements took place was explored in Power of Movement in Plants (1880). In this book Darwin explored plant tropisms, or the manner in which plants were able to grow toward light. He determined that the stem bends toward the light because of differential growth rates: the illuminated side grew more slowly than the unilluminated side so that shoot tips appeared to bend toward the light. He postulated the existence of a substance that was diffused from the apex downward that affected growth rates. These investigations anticipated the existence and action of plant hormones.

Darwin then directed his attention to other types of movements in plants, including mechanisms for prey capture in insectivorous plants such as the sundew, Drosera rotundifolia (1880). After detailed observation and experimentation, Darwin concluded that carnivorous plants had acquired the ability to live in nitrogen-poor soil with little or no root structure by feeding on prey. In addition to developing sensory apparatus to detect and capture prey, plants had also developed a digestive system capable of breaking down proteins. Most of these observations, including experiments with the sundew plants, were the focus of his book Insectivorous Plants (1875).

Darwin's last book relating to plants was a work with a strangely ecological theme: the action of worms in turning up soil. After experiments that ran for more than fifty years, Darwin postulated that earthworms played a vital ecological role: they fed on dead leaves and other organic matter and excreted this back into the soil. In so doing, earthworms served to aerate the soil and recycle vital nutrients. These results, including quantitative estimates of how much soil was processed by earthworms, were included in The Formation of Vegetable Mould Through the Action of Worms (1881).

Darwin's botanical work is notable for its detailed observations and simple, elegant experiments. These were performed in the confines of Darwin's backyard or at greenhouses at his home in Downe. Despite the fact that some of these are now classic experiments reproduced by students the world over, they were judged harshly by the leading German plant physiologist of the late nineteenth century, Julius von Sachs (1832-1897). A revolutionary experimentalist who introduced powerful analytical laboratory methods to botanical science, launching the "New Botany," Sachs thought Darwin's naturalist tendency and simple backyard experiments to be antiquated and amateur. Nonetheless, Darwin's botanical work remains the cornerstone of his studies on variation and mechanisms of adaptation in plants and is significant for his keen insights.

The book on earthworms was published just six months before Darwin's death. Until his end, Darwin remained a productive scientist. Some of his most imaginative work was performed toward the end of his long life. His was a happy and productive life in a home filled with the voices of his ten children and numerous grandchildren. On his death in 1882, he received a rare honor for a scientist: he was given a state burial and was buried at Westminster Abbey.

SEE ALSO CARNIVOROUS PLANTS; COMPOST; EVOLUTION OF PLANTS; EVOLUTION OF PLANTS, HISTORY OF; HOOKER, JOSEPH DALTON; MENDEL, GREGOR; ORCHIDACEAE; PHYLOGENY; SACHS, JULIUS VON; TROPISMS AND NASTIC MOVEMENTS.

Vassiliki Betty Smocovitis

Bibliography

Allan, Mea. Darwin and His Flowers: The Key to Natural Selection. New York: Taplinger, 1977.

Bowler, Peter J. Charles Darwin: The Man and His Influence. Cambridge, UK: Cambridge University Press, 1990.

Browne, Janet. Charles Darwin: Voyaging, Vol. 1. New York: Alfred A. Knopf, 1995.

de Beer, Gavin. "Charles Darwin." In Dictionary of Scientific Biography, Vol. 3, ed. Charles Coulston Gillispie. New York: Scribner's Sons, 1970.

Desmond, Adrian, and James Moore. Darwin. London: Michael Joseph, 1991.

Huxley, Julian, and H. B. D. Kettlewell. Charles Darwin and His World. New York: Viking Press, 1965.