Twin data on hand clasping: a reanalysis.

Abstract

Individuals can be classified into two categories, according to the way of per forming hand clasping: R type, when the fingers of the right hand occupies the uppermost position (sec fig. in Rothschild, 1930), and L type, when the opposite situation occurs (see fig. in Winchester, 1958). Each person has his peculiar way of clasping his hands, and it is believed that the type persists unchanged throughout the whole life. The reason why some persons clasp the hands with the fingers occupying one position, and not the other, is as yet unknown. This fact cannot be explained by relatively large differences in the shape and proportions of the bones of the hand, since it has been shown that a close over-all similarity between them exists (Greulich, 1960). We suggest, however, that even the small differences detected can explain the situation.Dahlberg (1926), based on twin and populational data, concluded that “there is hardly reason to presume heredity” in the genesis of the trait. His data can be explained well on the basis of a chance distribution, but this hypothesis can not account for the extensive amount of family data (Lutz, 1908; Yamaura, 1940; Kawabe, 1949; Yoshiwara, 1957; and Freire-Maia, Quelce-Salgado and Freire-Maia, 1958), as well as for the large amount of populational data (see Freire-Maia et al. 1958; Yoshiwara, 1957 ; Freire-Maia, 1961), and the ethnic, sex, and age differences detected (see Freire-Maia et al. 1958). Although all those authors presented strong evidences of a genetic component on the genesis of the trait, no simple Mendelian mechanism could explain the data, however.