Evolution is a theory that describes the way in which organisms change over time as a result of natural selection.Organisms best suited to their environment are more likely to survive and reproduce, passing their characteristic to their offspring. Gradually species change over time to have a more advantageous genotypes for the environment in which it lives.Darwin studied finches of the Galapagos islands. Different islands had finches with beaks and claws of different shapes and sizes.The design of the beaks was correlated with the food available on each island.At around the same time as Darwin, Alfred Wallace was working on a similar theory and sent his ideas to Darwin in 1858 for peer review before publication.In 1859 Darwin published the Origin of Species, a book that was very controversial at the time.