In 1859, On The Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life, the English naturalist Charles Darwin (1809-1882) explains his theory of evolution. His proof is based on two observations. All living beings, he says, are likely accidental individual variations related to the use or non-use of any organ or external conditions (climate, food, etc..) In which they are placed . At the same time, the multiplication of species on the surface of the earth causes a struggle for existence. Therefore ensures Darwin, individuals have variations that give them an advantage in this fight and they will transmit to their offspring. This is what he called natural selection. The action of the latter over a long period allows divergence of character and thus the formation of new species. Conversely, natural selection determines the extinction of the less improved forms. In many cases, sexual selection, which ensures the best adapted males a larger number of offspring is added to it. Darwinian theory, constantly reworked, still constitutes the general framework of the research conducted by biologists.
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