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A unidirectional evolutionary change among a related group of animals.



the hypothesis that evolution proceeds directly toward higher adaptive states.

Orthogenesis is rooted in the views of J. B. Lamarck. The German scientists W. Haacke, who introduced the term “orthogenesis,” and G. H. T. Eimer, who used this term extensively, proceeded from the mechanistic Lamarckian position that the direction of evolution is controlled by the immediate influence of the environment and that the internal organization of an individual can change only in certain set directions. Subsequently, “orthogenesis” was often used to describe evolution as being controlled by an internal driving force as well as by the immediate influence of the environment.

Modern evolutionary theory, according to which the direction of evolution is a result of natural selection, usually contradicts the concept of orthogenesis. Although linearity is a feature of evolutionary change, modern theory attributes it to limitations imposed on the structural features of the organism; linearity essentially is the result of natural selection in past generations. (See AUTOGENESIS, LAMARCKISM.)


Simpson, G. G. Tempy i formy evoliutsii. Moscow, 1948. (Translated from English.)
Shmal’gauzen, I. I. Problemy darvinizma, 2nd ed. Leningrad, 1969.
Haacke, W. Gestaltung und Vererbung, Leipzig, 1893.
Eimer, G. H. T. Die Entstehung der Arten. part 2: Die Orthogenesis der Schmetterlinge. Leipzig, 1897.