n. [ From Lamarck, a distinguished French naturalist. ] (Biol.) The theory that structural variations, characteristic of species and genera, are produced in animals and plants by the direct influence of physical environments, and esp., in the case of animals, by effort, or by use or disuse of certain organs. It is a discredited theory, not believed by modern biologists. [ 1913 Webster +PJC ]

n. (Biol.) Lamarckism as revived, modified, and expounded by recent biologists, esp. as maintaining that the offspring inherits characters acquired by the parent from change of environment, use or disuse of parts, etc.; -- opposed of Neo-Darwinism (which see, above). This theory has been thoroughly discredited, though it had some support for a time in the Soviet Union due to the influence of the biologist Lysenko.-- Ne`o-La*marck"i*an, a. & n. [Webster 1913 Suppl.]