Charles Robert Darwin, 1809-1882, laid the foundation of modern evolution and the theory of natural selection. He was the fifth born, Ferbruary 12th, 1809 in Shrewsbury, Shropshire, England, to a wealthy English family and grew up in a time when biologists generally agreed upon the catastrophic theory, or the theory that each species was created divinely and uniquely, and that they did not change at all over time. In 1825 Darwin attended the University of Edinburgh to study medicine, only to drop out in 1827 and attend the University of Cambridge to prepare to become a clergyman of the Church of England. There he met Adam Sedgwick, a geologist, and John Steven Henslow, a naturalist. Henslow taught him how to observe natural phenomena meticulously and thoroughly and to be a collector of specimens. In 1831 a 22-year-old Darwin graduated from Cambridge and, by Henslow's recommendation, was taken aboard the Beagle, an English survey ship, as an unpaid naturalist.

Darwin was able to observe different geological formations as well as a vast array of fossilized and living organisms while aboard the Beagle, and he was most impressed with the great effect that natural forces had on the shape of the earth's surface.

At this point the majority of scientists still adhered to the catastrophic theory, but a few, such as the English geologist Sir Charles Lyell, began to challenge the viewpoint. Over three years (1830-1833) Lyell published three volumes called Priciples of Geology stating that the earth's surface is undergoing constant changes due to the uniform operation of many natural forces. What Lyell did not oppose in the catastrophic point of view, however, is that species are immutable, or uniquely and divinely created. When Darwin was observing aboard the Beagle, he realized that some of his observations of fossils and living organisms did not support this viewpoint. He compared fossils of supposedly extinct species and living species in the same area and saw that although they were not identical, they were very similar. He also observed that in the Galapagos Islands off the coast of Ecuador each island supported its own separate form of tortoise, mockingbird, and finch -- forms that were different in structure and eating habits but very closely related otherwise. These observations made clear to Darwin the possibility of links between species that are separate but similar.

When Darwin returned to England in 1836, he began to record his revolutionary ideas about the changeability of species in his Notebooks on the Transmutation of Species. His explanation for the evolution of organisms was brought into sharp focus when he read An Essay on the Principle of Population written by the British economist Thomas Robert Malthus in 1798, which explained how human populations remain in balance. Malthus' argument was that human population grew exponentially, while food supply grew steadily, and the need of food would thus soon exceed its availability. He stated that because of this, human population growth must be checked by natural limitations, such as famine and disease, or by social actions, such as war and murder.

Darwin applied Malthus' argument to his own theory and by 1838 he had developed a sketch of evolution through natural selection. For the next twenty years he worked on his theory as well as other natural history projects. In 1839 he married his first cousin, Emma Wedgwood, and moved to Down House, a small estate outside London. There he and his wife had ten children, three of whom died in infancy.

In 1858 Darwin's theory was first announced in a paper that was presented at the same time as one by Alfred Russel Wallace, a young naturalist who had come to the theory of natural selection through independent study. Darwin's complete theory was published in 1859 in On the Origin of Species; it is often referred to as the "book that shook the world" -- the Origin sold out on the first day of publication and as a subsequence went through six editions.

The essence of Darwin's theory of evolution by natural selection is that because of the food-supply problem suggested in Mathus' publication, the young born to any species compete intensly with its peers for survival. The young that possess favorable charactaristics -- variations of characteristics that tend to aid in survival of the species -- are the ones to survive and thus pass on hereditary information. Over time these variations will become common among all organisms in the species and each generation will continue to be an improvement to the one preceding it, leading to the gradual evolution of entirely new species than the original. Besides this, Darwin also introduced the concept that all related organisms are descendants of common ancestors, and maintained the idea that the earth is constantly evolving rather than static.

Darwin's theories were met with immediate and extreme reactions from the reading public. Biologists argued that Darwin could not prove his hypothesis, nor could he explain the origin of variations and how they were passed from generation to generation. This objection went unanswered until the twentieth century with the emergence of modern genetics and the discoveries of Gregor Mendel. Scientists were not the only objectors, however, nor were they the most vehement. Religious opponents were disturbed that Darwin's theories debunked the idea of divine creation and placed humans on the same plane as animals.

Darwin spent the rest of his life expanding on his theory to resolve some questions raised by the Origin. He later published many books, including The Variations of Animals and Plants Under Domestication(1868), The Descent of Man(1871), and The Expression of the Emotions in Man and Animals(1872), which were detailed expositions of topics that had been confined to small sections in the Origin. Because his work was considered to be so very important to society by his contemporaries, Darwin was elected to the Royal Society in 1839 and the French Academy of Sciences in 1878. At his burial he was honored in Westminster Abbey after his death in Downe, Kent, on April 19, 1882.