READ: Gallery — Voyage of the Beagle

The HMS Beagle, captained by Robert FitzRoy, set sail from Plymouth Sound in England on December 27, 1831. Initially planned as a two year survey expedition, the voyage lasted nearly five years and circumnavigated the world. Darwin recorded his observations in journals and later published them in 1839.

Charles Darwin, shown here at age 45, was 22 years old when he set out on the HMS Beagle. Darwin's education included medicine and theology but his greatest passion was study of the natural world. His observations while the Beagle sailed around South America became the basis for his theory of natural selection.

This illustration, originally published with Darwin's writings and discussed in the excerpts here, shows four "sub-groups" of Galapagos finches. The different finches evolved with different beaks on different islands, as natural selection favored the beak that was best able to access the food sources of each bird's home island.

It was while visiting the Galapagos Islands, off the coast of Ecuador, that Darwin made some of his most important observations. In this group of volcanic islands, seen here from space, Darwin observed related species that had evolved differently on different islands. The unusual geology and the unique nature of the different islands had created numerous independent ecosystems, each with their own group of "naturally selected" creatures.

While Darwin visited Argentina in 1833 he explored the coast and walked inland where he discovered the fossils of many different creatures. Near Punta Alta, the plains (sometimes called the Pampas) revealed the previous existence of large land animals. This illustration is an artist's impression of some of the strange creatures that Darwin recorded, including the Toxodon, the long-necked Macrauchenias and the armadillo-like Scelidotheriums.

The Beagle sailed around the tip of South America and passed Tierra del Fuego – Spanish for "the land of fire." Darwin's journey would continue north from there to the coast of Chile and eventually to the Galapagos Islands off the western coast of Ecuador.