Peter Simon Pallas (1741-1811) was a German zoologist and botanist. He developed a new system for the classification of animals, based on his theory of historic development in the natural world and his idea that organisms could be represented like a family tree, showing sequential relations among the different taxonomic groups. In 1767, Pallas was invited by Catherine II of Russia to became a professor at the St Petersburg Academy of Sciences and, between 1768 and 1774, he led an expedition to central Russian provinces, collecting natural history specimens. Between 1793 and 1794, Pallas led a second expedition to southern Russia, visiting the Crimea and the Black Sea.