Quantitatively assessed familial sinistrality in right-, mixed-, and left-handers

Abstract

Numerous manifestations of cerebral asymmetry in man depend on the presence of non-right-handers (NRHs) among the subject's biological relatives – familial sinistrality, FS. This study proposes a method for a quantitative assessment of FS, based on the coefficient of relatedness of the subject with every single one of his/her relatives with known handedness. Such an approach conforms much better with the genetic principles than the methods ignoring the degrees of genetic relationship. Contacting and including as many as possible living relatives enlarges the category of subjects with FS, even relative to studies where non-immediate family members have been included and this enlargement might be especially important for the right-handers. The method was applied on a sample of 870 subjects (264 right-, 246 mixed- and 360 left-handers). Handedness, either distributed in the three classical categories or presented by the raw handedness score as continua, showed a highly significant relationship with the index. A considerable excess of females over males in their FS was found and its possible genetic and psycho-sociological reasons were discussed. It was suggested that the proposed method mirrors an existing biological reality and could be applied in further studies of handedness in relation to its genetic grounds.

Keywords:

• Handedness
• Familial sinistrality
• Quantitative assessment

Acknowledgements

This paper is dedicated to the memory of my unforgettable wife Dr. Pavlinka Kareva (1948–2007), an excellent pediatrician and an exceptional spouse and mother. The author gratefully acknowledges the Bulgarian Ministry of Education and Science for the authorization to perform this study and the National Science Fund at the Ministry for financially supporting this research under Contract No 1209, the school-heads and the teachers for the understanding and cooperation in the field work, and last but not least, all the secondary-school students who enthusiastically volunteered as subjects. I am also deeply indebted to the action editor and to two anonymous referees for the helpful comments and suggestions.