 Another characteristic of 19th century (and early 20th century) biology was the lack of a clear conceptual parting between developmental and reproductive processes. Especially the idea of the inheritance of acquired characteristics was part of the mainstream of evolutionary thought (Bowler 1983, 2017; Gissis &amp; Jablonka 2011). According to Jean Baptiste Lamarck (1809), changes in the structure or function of traits that occurred during an organism’s life, depending on their use or disuse, could be inherited. Darwin adopted this idea in his inheritance theory of pangenesis (see Holterhoff 2014). He suggested that all body parts, at each developmental stage, contain small particles, so-called ‘gemmules,’ that were sensitive to environmental changes. These particles accumulate in the reproductive organs and are transmitted to the next generation. Thus, gemmules modified during development lead to modifications in the next generation. Darwin stated that due to this close connection of development and reproduction, “inheritance must be looked at as merely a form of growth” (Darwin 1868: II, 404). However, this connection between development and inheritance was increasingly criticized in the first half of the 20th century. Following August Weismann (1892), the inheritance of environmentally induced variation in somatic cells (the body) of organisms was increasingly called into question. In sexually reproducing organisms, only the germ plasm used for the sperm and eggs were recognized as carrying information that are passed on to the next generation. According to this view, the germ line was immune from variation occurring in the somatic cells of the body, and thus the inheritance of acquired characteristics or other theories of plasmatic inheritance were rejected (but see Harwood 1993, Gilbert &amp; Epel 2015). 