Plate from 'The Zoology of the Voyage of HMS Beagle', published in London, 1839-1843, and edited by the British originator of evolutionary theory Charles Darwin (1809-1882). Vampire bats feed on the blood of sleeping animals. A chemical in the saliva stops the blood clotting. Unlike the legends, vampire bats do not attack humans. Darwin was naturalist on 'HMS Beagle' during its voyage of 1832-1836, the purpose of which was to make a scientific survey of the South American waters. Darwin's observations contributed to his discovery of the principle of natural selection of heritable variation as the cause of evolution. His most famous work, 'On the origin of species by means of natural selection', was published in 1859.
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