Lamarck was an 18th century French naturalist who is best known for his theory of evolution. He proposed this theory in his 1809 work Zoological Philosophy, and he believed that species evolve through the inheritance of acquired characteristics. Lamarck believed that use and disuse of body parts causes changes in those parts, which can be passed on to offspring.
His ideas were largely rejected by the scientific community at the time, and his theory was later disproven by experiments conducted by August Weismann. Lamarck’s theory is now considered to be an early, incomplete understanding of evolution. However, his work did contribute to the development of the modern theory of evolution—his ideas about the inheritance of acquired characteristics are now known to be incorrect but his work did contribute to this idea being developed further.