Developmental Aspects of Left-handedness

Investigations to explore human handedness have been conducted for ages. It is still uncertain what causes people to use the left or the right hand. Clues supporting the genetic origin of handedness have been accumulating and provide the best evidence. Nevertheless, in some populations there are different types of left-handers that do not seem to be explained solely by genes and differ from others for pathological reasons. An increased frequency of left-handers in clinical populations with central nervous system disorders may be due to early brain injury. Thereby, some birth stress or pathological factors may disrupt normal development and causing a switch in hand preference. It is commonly taken that interactions between a strong genetic influence and early life environment (pre, peri and post-natal) and learning processes play a role in the actual manifestation of hand preference.