L0025600 (lə-mär′kĭz′əm) also La·marck·i·an·ism(-kē-ə-nĭz′əm)n. A theory of biological evolution holding that the changes occurring in an organism through use and disuse of its body parts in response to environmental change are inherited by its offspring.[After Chevalier Jean Baptiste Pierre Antoine de Monet de Lamarck.]EncyclopediaSeeLamarckism