He set sail on HMS Beagle in 1831, and disembarked at Punta Alta in Patagonia where he made his first major find: gigantic fossils of extinct mammals. He spent three and a half years on land, and 18 months at sea (despite suffering terrible seasickness), collecting hundreds of specimens, making notes on plankton and marine life, and travelling into the interiors to study indigenous peoples. By the time he returned to England in 1836, he was a celebrity.
Darwin was not the first scientist to suggest the ideas that would make up the theory of evolution by natural selection, but his ground-breaking book On The Origin of Species (1859) has forever linked his name to the theory. The theory is itself still evolving.