In 1859 Darwin published On the Origin of Species, the first of a series of texts explaining the role of natural selection in the evolution of biological species. Central to his theory was a search for a mechanism of evolution; he also suggested that humans and other primates evolved from common ancestors. Darwin’s ideas were formulated primarily from his travels on the Beagle, a British ship that had sailed on a five-year voyage around the world during the 1830’s in order to map the globe and to collect flora and fauna. When Darwin published his account of the voyage in 1845, his ideas on evolution were already developing; however, it was another fourteen years before these ideas were formally published. Reasons for this long delay remain unclear. The most likely explanation is that Darwin’s materialistic view of evolution—which attributed natural selection to random variation—was so at odds with the views of religion and society that he was afraid of committing professional suicide with its publication. It was only after evidence supporting his view became more abundant that Darwin decided to publish his work.

The first public forum for Darwin’s theory came in June, 1860, at an Oxford meeting of the British Association for the Advancement of Science. As part of the public debate, Samuel Wilberforce, the bishop of Oxford, argued vehemently against any theory suggesting that humans were descended from apes. However, other scientists strongly defended Darwin’s arguments. Most prominent among them were the naturalist Thomas Huxley and botanist Joseph Hooker. Although Hooker had long opposed theories of evolution, he provided Darwin’s strongest defense. He accused Wilberforce of distorting Darwin’s work, and explained how he had become convinced of the truth of evolution.

Belief in evolution eventually became the norm among scientists. Prior to Darwin’s work, most naturalists believed that species were immutable, and that each had been created separately. Most notable among such “creationists” in the United States was Louis Agassiz, arguably the most important naturalist of nineteenth century America. However, while some scientists remained skeptical that natural selection was the driving force behind evolution, most became convinced that evolution itself was real. Thomas Huxley became known as “Darwin’s bulldog” for his strong advocacy of the theory. Although Huxley was an eloquent speaker, his extreme view of the Church often forced critics to take an opposing stand. Nevertheless, Darwin’s additional works on the subject of evolution, most notably Variation of Animals and Plants Under Domestication (1868) and The Descent of Man (1871), contained such strong arguments in favor of his theories that most critics were eventually quieted. By the early twentieth century, even most organized religions found little conflict with the idea of evolution or Darwin’s theories to explain it.