[Current aspects of handedness].

Handedness is one example of many forms of behavioural lateralization seen in humans. Left-handedness has existed in a small subset of the human population, approximately 8%, since the origin of man. The incidence of left-handedness is usually reported to be consistent among human populations. Sinistrality is more common in males than in females. A vast range of testing techniques have been used to assess handedness. There are preference and performance tests. Writing hand and self-report are two of the most popular techniques. There is a strong evidence that the dominance of language functions in the cerebral cortex is different in left-handed from that in right-handed people. An understanding of handedness may provide valuables clues as to how the brain becomes organized the way it is. Several theories have been advanced over the years to explain the genesis of handedness and, in particular, left-handedness. Theories have ranged from genetic models to socio-cultural theories. Other authors suggested a pathological origin of left-handedness in man. Left-handedness runs in families and adoption studies suggests a genetic rather than an environmental origin. However, monozygotic twins appear to be substantially discordant. A polygenetic explanation which takes environmental influences into consideration is probably called for.