Charles Darwin was a British naturalist whose theory or evolution by natural selection became the basis of modern theories of evolution. Darwin shocked the Victorians by suggesting that humans and animals shared the same ancestry. The Origin of Species is his most famous work. Darwin was aboard the Beagle in the Indian Ocean when he formulated his theory about the formation of coral reefs. Darwin theorized that coral reefs grew on sinking mountain rims. The delicate coral built up, compensating for the drowning land, so as to remain within optimal heat and lighting conditions.