Left-handedness two types
Left-handedness two types – Today we distinguish between left-handedness:
- genetic, occurring in patients whose left-handedness is genetically programmed,
According to an earlier theory neuropsychologist Norman Geschwind (1926-1984) the probability of left-handedness is more, if the fetus was exposed to increased concentrations of the male hormone testosterone, which affects the development of the cerebral hemispheres. This theory may explain why in the euro-american society among left-handers are more men (12%) than women (8%).
- pathological, the cause is the dominance of one cerebral hemisphere,
According to another theory, left-handedness is caused by problems during labor, as a result of oxygen deprivation causes damage to the brain. According to statistics among left-handers who have had complications during childbirth, 30% are mentally retarded.