Theodor Eimer

Gustav Heinrich Theodor Eimer (1843–1898) was a German zoologist.

Eimer was born in Zurich and in 1875, he became a professor of zoology and comparative anatomy at the University of Tübingen.

He is credited with popularizing the term "orthogenesis" (originally introduced by Wilhelm Haacke in 1893) to describe evolution directed in specific pathways due to restrictions in the direction of variation. Though his theories gained popularity in Germany in the 1880s, his work was not widely known in the English-speaking world until 1890 when his work "Die Entstehung der Arten auf Grund von Vererben erworbener Eigenschaften nach den Gesetzen organischen Waschsens"(1888) was translated by Joseph T. Cunningham as "Organic Evolution as the Result of the inheritance of Acquired Characters according to the Laws of Organic Growth". This book was predominantly a Neo-Lamarckian polemic against August Weismann, his compartriot Neo-Darwinian. Eimer's later work, translated as "On Orthogenesis", was a more rigidly orthogenetic text, whereas "Organic Evolution" maintained a plurality of mechanisms for species formation.

The "Eimer's organs" found in members of the mole family, especially in the Star-nosed Mole, are named after him. He described these organs in the European mole in 1871. Eimeria, a genus of parasitic protozoa, was also named after him.