Orthogenesis

Orthogenesis also known as orthogenetic evolution is an obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction due to some internal mechanism or "driving force".

American paleontologist George Gaylord Simpson (1953) in an attack on orthogenesis described it as "the mysterious inner force". Classic proponents of orthogenesis rejected the theory of natural selection as the organizing mechanism in evolution for a rectilinear model of directed evolution. The term orthogenesis was popularized by Theodor Eimer.

With the emergence of the modern evolutionary synthesis, in which the genetic mechanisms of evolution were discovered, the hypothesis of orthogenesis was refuted, especially with Ronald Fisher's argument in his 1930 book The Genetical Theory of Natural Selection in favour of particulate inheritance.

Orthogenesis was a term first used by the biologist Wilhelm Haacke in 1893.Theodor Eimer was the first to give the word a definition; he defined orthogenesis as "the general law according to which evolutionary development takes place in a noticeable direction, above all in specialized groups."

In 1922, the zoologist Michael F. Guyer wrote:

[Orthogenesis] has meant many different things to many different people, ranging from a, mystical inner perfecting principle, to merely a general trend in development due to the natural constitutional restrictions of the germinal materials, or to the physical limitations imposed by a narrow environment. In most modern statements of the theory, the idea of continuous and progressive change in one or more characters, due according to some to internal factors, according to others to external causes-evolution in a "straight line" seems to be the central idea.

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