“…As regards the primary link in the working hypothesis mentioned above, viz, that in respect of genes, monozygotic twins are identically equipped this presumption, also, has been subjected to doubt by Dahlberg (1930), Bottleneck (1934) and Newman, Freeman and Holzinger (1937) among others. The above mentioned authors, although with slightly differing formulation, attribute conclusive significance to the so-called "asymmetry phenomenon" as a theoretically possible source of error in the twin method and thus for its basic foundation.…”