Bilateral Variation in Man: Handedness, Handclasping, Armfolding and Mid-Phalangeal Hair

A study of bilateral variation among individuals from three populations was conducted. One sample consisted of 174 Cashinahua Indians who reside along the Curanja River in the Peruvian rain forest. A second group was composed of 286 students from anthropology classes at the University of Tennessee, Knoxville. Eighty-six families, including 372 individuals, constituted the third sample.

Four laterality traits - handedness, armfolding, handclasping, and mid-phalangeal hair - were analyzed by population and by individual family.

The most interesting variation occurred in the frequency of right and left handclasping and in the presence or absence of mid-phalangeal hair. The percentage of left and right armfolders among the populations was fairly stable. Handclasping and armfolding do not seem to be related to handedness, however, conflicting data on the relationship between armfolding and handclasping showed that further study is needed.

The Cashinahua differed more from the two Tennessee populations than the latter two did from each other. In particular, the frequency of mid-digital hair among the Cashinahua was very low, which is consistent with data from other American Indian groups. The two Tennessee populations, on the other hand, compared with other Caucasoid samples in hair frequency.

Analysis of the family data provided some evidence for the heritable character of the handclasping trait and strong evidence for the heritability of the mid-phalangeal hair trait. Armfolding and handedness, on the other hand, did not seem to reflect a strong genetic character.