1) Charles Darwin was a British naturalist born in 1809 who studied medicine and divinity before joining a scientific expedition on the HMS Beagle as their geologist from 1831-1836.
2) While traveling on the Beagle, Darwin was influenced by the ideas of Charles Lyell and observed unique species of finches on the Galapagos Islands, sparking his theory of evolution by natural selection.
3) After corresponding with Alfred Russel Wallace, Darwin published On the Origin of Species in 1859, introducing his theory that organisms change over generations through a process of natural selection, survival of the fittest, and gradual speciation from common ancestors.