Lev Semyonovich Berg, also known as Leo S. Berg (Russian: Лев Семёнович Берг; 14 March 1876 – 24 December 1950) was a leading Russian geographer, biologist and ichthyologist who served as President of the Soviet Geographical Society between 1940 and 1950. He is known for his own evolutionary theory, nomogenesis (a form of orthogenesis incorporating mutationism) as opposed to the theories of Darwin and Lamarck.