In December 1831, Charles Darwin boarded the HMS Beagle, accompanying her crew on a five-year journey that crossed the Atlantic Ocean to survey the coasts of South America. As the expedition's geologist and naturalist, Darwin collected evidence from the Galapagos Islands and other locations which prompted him to speculate that species evolve over generations through a process of natural selection. In 1859, Darwin published On the Origin of Species, a work of scientific literature considered to be the foundation of evolutionary biology. His revolutionary work presented evidence from the Beagle expedition as well as from years of subsequent research and experimentation.