 Schaffner’s case for reduction in genetics invited philosophers to take a hard look at the theories and practices of biologists. A variety of challenges to Schaffner’s thesis ensued. David Hull (1974) claimed that there was no neat connection between classical genetics’ gene concept and molecular genetics’ DNA sequence because there was no neat, one-to-one mapping between stretches of DNA and the traits that the classical geneticists investigated; instead, Hull thought it better to characterize molecular genetics as having replaced classical genetics. Philip Kitcher (1984) agreed with Hull that reduction was the wrong way to understand the relationship; however, he offered a different formulation of the correct way. Kitcher said it was best to understand classical genetics and molecular genetics as operating on different, autonomous levels; classical geneticists investigated the transmission of traits by studying the cytological mechanisms of chromosomal action, while molecular geneticists investigated things like gene replication and mutation by studying the molecular mechanisms of protein synthesis (entries:  molecular genetics;  the unity of science). 