As a young man, Charles Darwin joined a British scientific expedition aboard the H.M.S. Beagle. As the Beagle journeyed around the world, Darwin collected specimens of plants and animals. He found fossils of extinct animals that resembled living animals, and he noticed many variations within the same species. After returning from his voyage, Darwin spent twenty years studying his specimens. In 1859 Darwin published On the Origin of the Species by the Means of Natural Selection, a book that explained his new theory.
Creatures produce more offspring than can possibly survive.
Members of a species must compete for limited resources and for survival. No two members of a species are exactly alike. Each organism contains an individual combination of inherited traits. Organisms that have useful traits reproduce in greater numbers. Their offspring inherit the traits.