The Eclipse of Darwinism - Orthogenesis

Orthogenesis

Orthogenetic evolution was the hypothesis that life has an innate tendency to change, in a unilinear fashion in a particular direction. The term orthogenesis was popularized by a Theodor Eimer a German zoologist. Eimer also believed in Lamarckian inheritance of acquired characteristics, but he felt that internal laws of growth determine which characteristics would be acquired and guided the long term direction of evolution down certain paths.

Orthogenesis had a significant following in the 19th century, and its proponents included the Russian biologist Leo S. Berg, and Henry Fairfield Osborn, an American paleontologist. Orthogenesis was particularly popular among some paleontologists, who believed that the fossil record showed patterns of gradual and constant unidirectional change. Those who accepted this idea, however, did not necessarily accept that the mechanism driving orthogenesis was teleological (goal-directed). They also thought orthogenetic trends were not adaptive; in fact they felt that in some cases they led to developments that were detrimental to the organism, such as the large antlers of the Irish elk that they believed led to the animal's extinction.

Support for the orthogenesis hypothesis began to decline during the modern evolutionary synthesis in the 1940s when it became apparent that it could not explain the complex branching patterns of evolution revealed by statistical analysis of the fossil record by paleontologists. A few hung on to the idea of orthogenesis as late as the 1950s by claiming that the processes of macroevolution, the long term trends in evolution, were distinct from the processes of microevolution.