However, Morley (1972) found that some 26% sample of 96 children with articulatory difficulties were left-handed and another 14% were poorly lateralized. An increased incidence of handedness, therefore, may be specific to children showing early articulatory problems, rather than being characteristic of all developmental language problems (see Bishop 1990a) (p. 144). (Bryden, M. P., McManus, I. C. & Bulman-Fleming, M. B. (1994). Evaluating the empirical support for the Geschwind-Behan-Balaburda model of cerebral lateralization. Brain and Cognition 26, 50-151.)
Handedness is closely related to cerebral lateralization which is related to uterine testosterone levels. When studies conclude that later born and the first born child are more likely to get autism, looking for what effects lateratlization makes sense.
Children born later in the reproductive live of a mother are emerging from wombs bathed in higher levels of testosteone. That more of these children would be autistic makes sense. What would cause a first born child to exhibit autism?
Are first borns more often left handed? If left handedness is related to testosterone, we would predict that children born from older mothers would be more often left handed. If first born and later borns are both more often left handed, exploring the what causes lefthandedness would be useful.
If Sarah Blaffer Hardy’s conclusion that children with no alloparents and no older siblings exhibit a less robust theory of mind, then might less theory of mind and left handedness be connected?
The implication is that autism, left handedness, mother’s testosterone levels, and a childhood featuring only one motherlike figure may be all related.