The story of Charles Darwin's life is largely the story of how he discovered and found evidence for his theory of natural selection. Darwin's life fits a pattern that was typical for his era in England. He came from a well-established family of doctors, businessmen, and clergymen. He idled away his youth, eventually studying for the clergy at Cambridge. He returned from a long sea voyage, married, and settled in a quiet parsonage in the English countryside to nurse his health and work on science. His involvement in the question of evolution, however, makes his life emblematic of the ideological and cultural struggles going on around him. Evolution brought several questions of deep religious and cultural significance to a head. Among the divisive issues that evolution brought up were questions of how long the world had existed, whether or not humans were animals, and whether God was continuously intervening in the world or had created natural laws to govern it from a distance.
Although the story of evolution is largely one of scientific research and argument, it is also influenced by the social and cultural context within which Charles Darwin found himself. The first and most obvious enabling feature of Darwin's context was the status of England as an imperial power in the 19th century. With England's powerful navy and outposts from Tahiti to South America to Africa, an English ship had more and easier opportunities than any other nation's to explore the world. The voyage of the Beagle was actually part of England's empire-building effort. Without it, Darwin's theory of evolution would never have gotten off the ground.
A second important cultural factor was the changing political and ideological attitude in England. When Charles attended Cambridge to study for the clergy, the conservative Tories were in power. While he was away on the Beagle, the Tories fell from power and were replaced by a less conservative government that emphasized freedom of belief and freedom of commerce. The new attitude of freedom and competition, exemplified by Malthus's theory about the "struggle for survival," was a foreshadowing of Darwin's own theory of competition in the natural world.
While Darwin is properly credited with making evolution the dominant paradigm in biology, he was not the first to come up with the idea. In fact Darwin's major contribution was to suggest a mechanism for evolution–natural selection–that did not depend on the intervention of a divine power. There were three major revolutions in scientific thought that prepared the way for a successful theory of evolution.
The first major change in scientific thought was in the field of biology. Linnaeus, the Swedish biologist, had proposed the first successful taxonomy of all species of plants and animals. This taxonomy abandoned the theory of the chain of being that claimed that all living creatures formed and unbroken scale of complexity and nobility, terminating with the most complex and noble of all, humanity. Instead, Linnaeus showed that life could be divided into five separate kingdoms, each divergent from the others.
The rise of evolutionist thinking made the idea of a chain of being fall out of favor. By the 19th century, it was increasingly obvious from archaeological research that some species could become extinct and others could arise, apparently spontaneously. Conservative thinkers argued that these extinctions and creations were the work of an active God. However, others argued that there were natural, non-religious explanations for the extinction and creation of species. Darwin's own grandfather, Erasmus Darwin, proposed many of the ideas about evolution for which Charles would later find evidence. In his Zoonomia, published in two volumes in 1794 and 1796, he described the varieties of life in the world and suggested that new species arose from the modification of old ones. Although Charles claimed to have gotten little from Zoonomia, it is obvious that he read it carefully during his Cambridge years and it is likely that its passages on evolution influenced him.
The second major change in scientific thought was in the field of geology. Traditional Christian geologists held that the catastrophes described in the Bible, such as Noah's flood, had actually taken place and caused many of the signs of geological change that could be seen. This view was known as catastrophism. An alternative to catastrophism was the view called uniformitarianism. Proponents of uniformitarianism argued that the world's current geological state was the result of uniform forces working slowly over long periods of time. Uniformitarianism was one of the foundations of evolutionary thought, in part because it provided a geological analogy for biological change: both were the result of gradual forces working over extremely long time periods. One of the foremost exponents of uniformitarianism was Charles Lyell, whose Principles of Geology Darwin read during the voyage of the Beagle.
The third major change in scientific thought was in the conception of time. Traditional Christian views held that the world started with its Creation and would end with the second coming of Jesus. This concept did not give evolution enough time to producing anything. 6000 years was not enough time to create the incredible diversity of life in the world. A second way of viewing time was allied with uniformitarianism; it was that the earth had existed for an extraordinarily long time, more than long enough for a slow and gradual process like evolution through natural selection.
Darwin's theory of evolution brought these strands of thought together into a clear, cohesive argument about how the competition for life between individuals with varied traits could lead to near-infinite divergences in biological structure. It helped bring life further within the realm of science, and today it forms the conceptual framework within which all of biology is conducted.