What did Jean Baptiste de Lamarck mainly do?

Jean Baptiste de Lamarck was a French naturalist best known for his early theory of evolution, which proposed that organisms adapt to their environments through use and disuse of traits, a concept often summarized as "inheritance of acquired characteristics." He introduced ideas about species changing over time and the concept of "transformism," suggesting that life forms evolve from simpler to more complex organisms. Although his theories were later overshadowed by Darwin's natural selection, Lamarck's work laid important groundwork for the study of evolution.