Opossum, c 1832-1836.

UNSPECIFIED - JULY 16: 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). 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. The expedition also visited the Galapagos Islands, Tahiti, Australia and New Zealand. 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. (Photo by SSPL/Getty Images)