 As Novick and Scholl (forthcoming) show, a science of genetics that met the vera causa standard eventually emerged in the 20th century, in the wake of the re-discovery of Mendel’s laws as well as improved microscopic and cytological techniques. The latter were important, because they allowed independent checks of the structures that were invoked in order to explain the observed experimental regularities. A case in point is Thomas Hunt Morgan’s and his co-workers’ “proof” of the hypothesis that genes are parts of chromosomes (Bridges 2014). 