HANDEDNESS AND DIRECTIONAL ASYMMETRY IN THE LONG BONES OF THE HUMAN UPPER-LIMB

The long bones of the human upper limb usually show lateral asymmetries of length. This pattern can be attributed either to the mechanical consequences of handedness bias or to genetic or hormonal factors acting directly on longitudinal bone growth. Length data was obtained from the long bones of the upper limbs of a large skeletal assemblage from Wharram Percy, Yorkshire (England), predominantly deriving from the 11th-16th centuries A.D. The Wharram Percy adult skeletons had a population distribution of lateral asymmetries of length in the humerus and in the humerus-plus-radius (a proxy arm length index) which closely parallels the pattern of behavioural handedness found in modern populations. This pattern was developing in the skeletons from the infant and juvenile age ranges, but was absent in the neonates (of whom 12 out of 14 had longer left humeri). We argue that this supports the environmental hypothesis that the ontogeny of long bone length asymmetry is consequent to the earlier development of lateral bias in mechanical loading of the upper limbs.