Lamarckism [19th century; named after the biologist J.-B. Lamarck] address developed in biology since 1880 (also called neolamarckism), including a very heterogeneous group of theories of evolution that converged in supporting the heritability of acquired characters, the non-random or accidental origin of evolutionary variations or their strict dependence on environmental conditions. Rather than through a direct appeal to the theory of J.-B. Lamarck, then little known, arose as a contrast to the neo-Darwinism of A. Weismann, who rejected the inheritance of acquired characters (for example mutilations) arguing that the variations arise by chance in reproductive cells and are screened only by selection.

Typical of Lamarckism was the attempt to resolve the objections raised against Darwinian theories, according to which the most useful variations arising in some individuals of a group were destined to fade and disappear through crosses with individuals not endowed with the new characters. Lamarckism appealed to a potentiality or reactivity inherent in living matter to support the simultaneous emergence of new characters in all or almost all individuals of a group (R. A. K├Âlliker and T. C. Eimer), or argued that environmental influences inscribe the new characters in a cellular memory capable of transmitting them to descendants (E. Hering, R. Semon, E. Rignano, T. D. Lisenko). Others, closer to vitalism, considered the preeminent cause of changes the use and non-use of organs related to needs induced by the environment.

Since the end of the nineteenth century and in the first decades of our century Lamarckism has been engaged, rather than to formulate hypotheses to explain the origin of adaptive variations, in the defense of the heritability of acquired characters. However, the observations in favor of heredity were interpreted precisely on the basis of the opposite theory of non-heredity of these characters based on the distinction between somatic and reproductive cells, a fundamental assumption of the new genetics.