Left-handed

It is assumed that the formation of the dominance of a single human evolution is due. Man as the highest developed mammal could only achieve its development through the specialization of the cerebral hemispheres and a variety of links to the specific brain areas. The human brain is a highly complex system for controlling all functions of the human body. It consists of two connected halves of the brain, called cerebral hemispheres. These in turn are connected to the main nerve cords cross over with the two body halves. In simple terms, this means that the right hemisphere, the left side of the body and the left hemisphere controls the right side of the body. This is called "functional asymmetry". Thus, the cerebral hemispheres are also significantly involved in the expression of handedness. Especially critical to the question of handedness seems to be dominant hemisphere for language functions. Herein, in turn, justify any potential problems in speech processing and playback, as well as possible reading and spelling problems retrained left-handed (see also "follow a retraining of handedness").
A dominance occurs in the normal case, moreover, not only with respect. The hands on. It can be seen as well in the eyes, ears or legs. Frequently one hears also the concept of "cross-laterality", ie if for example the right hand, but the left eye or the left hand, but the right leg is dominant.

For a definition of handedness, it is important to take into account two basic aspects. On the one hand preference, i.e. the preference of one hand in the (spontaneous) hand use, and secondly, the power dominance. The latter provides an answer to the question of which hand in carrying out fine motor tasks such as the better results regarding speed or accuracy achieved (see also "What is a Händigkeitstest").
The dominant hand is characterized by the fact that she is with spontaneous actions of the protagonist and fine motor skills and dexterity, as regards the "better" so powerful hand. The non-dominant hand, however, has more hold and accompanied bimanual (both hands) actions. It has thus each hand their specific areas of responsibility.
The important thing is that handedness is not in the sense of either-or exists, but rather as a continuum. In rare cases, a person has comparable performance of both hands, one speaks of an ambidextrous, a so-called Beidhänder. The latter, however, are not to be confused with retrained lefties who have made a virtue of necessity, and then use both hands for some activities is können.Typisch however, that a right-handed with his left hand much more often than a left-hander uses his right hand. Left-handers are usually less significant differences in performance as right-handers.

Proportion of left-handers:
For many years, left-handers in all cultures to be rare. Reasons for this was seen both in the functional organization of the brain in genetic factors as well as in social conditions. By now, most studies are at a ratio of 30:70 between left-and right-handed people. There are also increasing number of studies published, which assume a uniform distribution. Especially among older people is often misunderstood because of the previously very high rate of re-training, the proportion of left-handed people.

Text: M. Zotter
Occupational Therapist
BSc "Occ. There."
(Bachelor of Science for Occuptional Therapy)

Literature:
Wikipedia (2012)