One of the most influential figures in human history is Charles Darwin. Darwin has been called the father of evolution for his work in evolutionary science. In the United States, Darwin has become the symbol for atheists in the country as his theory of evolution smacks in the face of creationism. His theory claims that all of earth's species have descended from their ancestors, and that they have adapted to their surroundings throughout history. It also claims that every species has a common ancestor. Darwin introduced his theory in his landmark book On the Origin of Species in 1859.
His book was met with suspicion from both the scientific community and the general public, but by the 1870s, his work was beginning to gain mass acceptance. One of his most significant studies came when he sailed with the HMS Beagle, a British sea vessel, to the Galapagos Islands. The islands have been long isolated from the South American mainland, and provided him with a unique insight on the process of evolution.
While sailing from island to island, Darwin noticed similarities between island species and mainland species. Most were similar in many ways, but some had subtle differences. He also found that the same species had differences from island to island. To Darwin it was clear that the reason for the slight differences was the individual environment of each island. These islands showed Darwin the evolution process in the making.
Darwin has many critics from religious circles. A very famous caricature of Darwin depicting him as a half-human monkey was published in 1871 in response to his theory that humans evolved from ape-like creatures. He spawned a movement of non-believers called Darwinism, which includes people who feel his theories are rooted in the scientific method as opposed to religious dogma.