Charles Darwin and Evolution by Means of Natural Selection
At his home, Down House, in Kent, Charles Darwin (1809–82) had a large garden that he loved and greenhouses in which he performed experiments. Although his evolutionary theory is most often discussed in its relation to animals, Darwin was every bit as interested in the evolution of plants. He used the way breeders modify animals by selectively breeding those individuals that possess the characteristics the breeders wish to emphasize as a metaphor for evolution by natural selection, and he applied exactly the same argument to plants. In the first chapter of On the Origin of Species Darwin wrote the following:
In plants the same gradual process of improvement, through the occasional preservation of the best individuals, whether or not sufficiently distinct to be ranked at their first appearance as distinct varieties, and whether or not two or more species or races have become blended together by crossing, may plainly be recognised in the increased size and beauty which we now see in the varieties of the heartsease, rose, pelargonium, dahlia, and other plants, when compared with the older varieties or with their parent-stocks. No one would ever expect to get a first-rate heartsease or dahlia from the seed of a wild plant. . . . I have seen great surprise expressed in horticultural works at the wonderful skill of gardeners, in having produced such splendid results from such poor materials; but the art, I cannot doubt, has been simple, and, as far as the final result is concerned, has been followed almost unconsciously. It has consisted in always cultivating the best known variety, sowing its seeds, and, when a slightly better variety has chanced to appear, selecting it, and so onwards.
Darwin did not discover that the plants and animals living today have evolved from earlier forms. By the middle of the 19th century many biologists had reached this conclusion, but none had proposed a credible mechanism by which evolution might occur. That is the contribution Darwin made. His proposal was simple, persuasive, and although there were many difficulties with it, which he was the first to acknowledge, the vast amount of evidence that has accumulated since his death has resolved those difficulties and demonstrated that his idea was essentially correct. He outlined his theory in On the Origin of Species by Means of Natural Selection: Or the Preservation of Favoured Races in the Struggle for Life, published in 1859. The theory can be summarized as:
- There is variation among the individuals of every species.
- Those variations are heritable.
- On average, parents produce more offspring than are needed to replace them (i.e., more than two offspring for each set of parents).
- Populations cannot increase indefinitely and in most populations numbers remain fairly constant.
- It follows that there must be competition among offspring in each generation.
- In that competition, the individuals best fitted to the conditions under which they live will gain better access to resources and tend to produce more offspring.
- Over time, environmental conditions change, and as they do so the qualities that best suit organisms to their environment also change; thus the environmental conditions determine which individuals will produce most offspring. This is natural selection.
- Offspring will inherit the characteristics that equipped their parents for the environments in which they lived.
- The resulting changes will accumulate over many generations, as changing environmental conditions select individuals possessing characteristics that best equip them for the new conditions, until they result in the emergence of new species. This is the origin of species by means of natural selection.
Charles Robert Darwin was born into a prosperous family in Shrewsbury, Shropshire, England, on February 12, 1809. He was the fifth of six children and his parents' second son. His education began in September 1818 when he enrolled as a boarder at Shrewsbury School, joining his brother Erasmus Alvey Darwin (1804–91). In October 1825 Darwin spent the summer helping his father who was a physician, before he and Erasmus both went to the University of Edinburgh to study medicine. Charles learned taxidermy—the craft of posing dead animals in lifelike attitudes for display—but found surgery distressing and spent much of his time studying natural history. He left Edinburgh, and in January 1828 entered Christ's College, Cambridge, to commence a course of studies intended to prepare him for becoming an Anglican clergyman. While there he grew friendly with a number of naturalists, including the professor of botany John Stevens Henslow (1796–1861).
Darwin did well in his final examination in 1831, and later that year he was accepted as a companion to Robert FitzRoy (1805–65), who was preparing to sail around the world on a surveying expedition as captain of HMS Beagle. The voyage lasted almost five years, returning to England on October 2, 1836.
Following his return, Darwin lived for a time in Cambridge and then moved to London. He was under tremendous pressure of work. He had to write and correct his Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage of H.M.S. Beagle Round the World, Under the Command of Captain FitzRoy, R.N., more often known as The Voyage of the Beagle, for inclusion in the official report of the voyage. He began editing and preparing the reports on his zoological collections written by various experts as well as Darwin himself. These were published between February 1838 and October 1843 in five volumes as Zoology of the Voyage of HMS Beagle Under the Command of Captain FitzRoy, R.N., during the Years 1832 to 1836.
He had agreed to write a book on geology, and in March 1838, after resisting for a time, he accepted the post of secretary to the Geological Society of London. His health began to deteriorate, and he never recovered. From that time he was prone to attacks of stomach pains and vomiting and suffered from headaches, palpitations, boils, and other symptoms. The cause of his illness was never diagnosed, but the symptoms were especially severe whenever he had to attend meetings or social events, which he found stressful.
On January 24, 1839, Darwin was elected a fellow of the Royal Society, and on January 29 he married his cousin, Emma Wedgwood (1808–96). The delighted family gave them a dowry and investments that brought them in an income on which they could live in comfort for the rest of their lives. In 1842 the couple moved to Down House, bought for them by Darwin's father, and that is where they spent the rest of their lives. Darwin continued with his research and writing. He published The Descent of Man, and Selection in Relation to Sex in 1871, The Expression of Emotions in Man and Animals in 1872, as well as a number of books on botany, and an autobiography that was published in 1887. The illustration on previous page shows him toward the end of his life. Darwin died at Down House on April 19, 1882. His funeral was held in Westminster Abbey, where Darwin is buried.
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