FAMILY PATTERNS IN HANDEDNESS - EVIDENCE FOR INDIRECT INHERITANCE MEDIATED BY BIRTH STRESS

The most common alternative to a genetic explanation of left-handednes s is that sinistrality arises because of birth stress factors. In a sa mple of 1398 subjects, the association between birth stress and left-h andedness was confirmed. More importantly, it was found that left-hand ed mothers are more likely to have birth-stressed offspring and that t he presence of any left-handed sibling increases the likelihood of a h istory of birth stress in the proband. This was interpreted as suggest ing that a plausible alternative to the genetic explanation for the us ual pattern of association observed in family studies of handedness (w here a left-handed mother increases the probability of left-handed off spring) is that the mother-offspring association may actually be media ted by birth stress rather than representing heritable aspects of hand edness.