Mendelian inheritance
Studiers of evolution such as Lamarck and those who postulated the inheritance of acquired characteristics (e.g. Theodor Eimer and Edward Drinker Cope) were concerned with heredity and sought a link between one generation to the next. Lamarck thought that bodily responses from one generation should be passed along to future generations, which Wright refers to as "direct evolution". Sewall Wright expresses that the birth of genetics stems from Mendelian inheritance principles and so "any theory of evolution" must also be based on Mendelian inheritance.