title: Theodor Eimer and orthogenesis: evolution by 'definitely directed variation'.
mesh_terms: D005075:Biological Evolution; D014644:Genetic Variation; D005858:Germany; D049672:History, 19th Century; D049673:History, 20th Century; D012641:Selection, Genetic; D006113:United Kingdom; D014481:United States; D015046:Zoology / Q000266:history*