 Besides this increasing conceptual parting, however, evolution and development were considered to be closely interrelated processes by many scholars throughout the 19th century. By building on earlier comparative studies of embryonic processes across various taxa (among others by Karl E. von Baer (1827) and Fritz Müller (1864)), Ernst Haeckel (1872) argued that all metazoans have the same early stages of development (see Gould 1977). He understood these developmental patterns as modifications of a basic type. According to this biogenetic law, the development of individuals is a recapitulation of species’ evolutionary changes: