Definition
Orthogenesis was a term first used by the biologist Wilhelm Haacke. 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."
Orthogenesis was often related to Neo-Lamarckism; Eimer popularized the concept of orthogenesis in his book Organic Evolution as the Result of the Inheritance of Acquired Characteristics According to the Laws of Organic Growth (1890). In his work Eimer used examples such as the evolution of the horse to argue that evolution had proceeded in a regular single direction that was difficult to explain by random variation. To orthogenesis trends in evolution were often nonadaptive and in some cases species could be lead to extinction.
Peter J. Bowler defines orthogenesis as:
Literally, the term means evolution in a straight line, generally assumed to be evolution that is held to a regular course by forces internal to the organism. Orthogenesis assumes that variation is not random but is directed towards fixed goals. Selection is thus powerless, and the species is carried automatically in the direction marked out by internal factors controlling variation.
According to (Schrepfer, 1983):
Orthogenesis meant literally "straight origins", or "straight line evolution". The term varied in meaning from the overtly vitalistic and theological to the mechanical. It ranged from theories of mystical forces to mere descriptions of a general trend in development due to natural limitations of either the germinal material or the environment... By 1910, however most who subscribed to orthogenesis hypothesized some physical rather than metaphysical determinant of orderly change.
Orthogenesis has been described as an "anti-Darwinian" evolutionary theory because of its stance on the Darwinian mechanism of natural selection. After studying butterfly coloration Theodor Eimer published a widely read book on orthogenesis titled On Orthogenesis: And the Impotence of Natural Selection in Species Formation (1898). In the book Eimer claimed there were trends in evolution with no adaptive significance and thus would be difficult to explain by natural selection. Stephen J. Gould wrote a detailed biography of Eimer. Gould wrote that Eimer was a materialist who rejected any vitalist or teleological approach to orthogenesis and explained that Eimer's criticism of natural selection was common amongst many evolutionists of his generation as they were searching for alternative evolutionary mechanisms as it was believed at the time that natural selection could not create new species.
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