Handedness

The term handedness describes the phenomenon that primates, including humans, for fine motor activities consistent hand preference, the dominant hand so called.

Handedness

People are so-called one-handed: Challenging tasks are each uniquely distributed between the right and left hand. The hand wielding the pen or the needle, for example, is called "dominant" - albeit about the neurologist Frank Wilson puts into perspective the uniqueness of the concept of dominance. The anticipatory and supportive activities of the non-dominant hand is just as sophisticated as the activity of the tool leading dominant hand.

Noticeable in this context is the high number of right-handers. The proportion of left-handers in the European population is given by the German Society for Occupational and Environmental Medicine 10 to 15 %. The proportion of so-called Beidhändern is a matter of definition: For driving a broom or brush to use over 60% of right-handed and about 99 % of left-handers and the non-dominant hand, the more demanding but the tasks are, the more clearly the intention of the proportion of functional Beidhänder to zero.

A clear over-representation of right-handedness is found in all well- examinable human cultures; historical or geographical differences can not be determined. The analysis of archaeological finds (such as the investigation of tools to scuffs ) suggests that even the Neanderthals, extinct relatives of modern humans, predominantly right-handed were. For other " ancestors " of man, this can not clearly ascertain because the finds ( bones, tools, ... ) are often not sufficient to make statements about handedness or even preferred in a population hand. For the present majority is right-handedness can be observed in all civilizations. Consequently, biological reasons to be adopted. Since handedness in families is passed frequently, a quarter of all monozygotic twins but have different handedness, it is nowadays of hereditary tendencies, do not follow the Mendelian laws. Recently, genetic explanations are clarified and has been named on chromosome 2, a specific location.

" Handedness " in animals

Typical asymmetries of the nervous system can be observed already in the soft and crustaceans. Rats, cats and monkeys prefer all of their limbs to carry out demanding tasks, however, are " ambidextrous " each about equally represented. Apes show (similar to the human ) for simple tasks no pronounced handedness; the more complex the task, the clearer it becomes a standardized roles of the hands even with them. A predominant group-level handedness, however, was observed only occasionally it is thought that bonobos left hand, common chimpanzees prefer for wearing for throwing the right hand.

Laterality of brain and hand

Findings from studies on the lateralization of the brain show that it is predominantly the left hemisphere for motor control of the right side of the body and the right hemisphere for the left side of the body is responsible.

As the " dominant" hemisphere of the brain is called the one that is primarily responsible for the processing of language. In 95% of right-handed she is on the left, at 2% right. At 3 %, the Language Center is divided between the two halves of the brain. Also, in the majority of left-handers, the Language Center is on the left, namely at 70 %, at 15 % it is distributed over both hemispheres, with a further 15 % it is right. So there is a certain correlation between the " dominant" hemisphere of the brain and that brain, which controls the strong hand. Nevertheless, the speech center is in the majority of left-handers on the left side, which is responsible for the "weak " right hand. Thus, there is no clear law before the connection of handedness and lateralization of the brain. If one assumes a 10% share of left-handers, are about 7 % of the population control of the "strong" hand and the speech center in different halves of the brain - without reprisal.

Through targeted magnetic pulses (transcranial magnetic stimulation, TMS ) over the motor cortex was the choice of hand for a simple activity are temporarily " switched ".

Advantages of handedness

In the evolution of the hemispheric specialization of the brain has probably enforced because then the two cerebral hemispheres could not compete with each other. Benefits of Einhändigkeit against the ambidexterity be seen in greater precision of manual labor by specific training. Unclear are the advantages of a majority right-handedness. By Thomas Carlyle to the " battlefield " theory arises and according to the soldiers the right weapon and left the shield wore, so they could protect her heart better. However, shields only since the Bronze Age in use, so for about 5000 years, and even the much earlier living ( about 2 million years ago) primitive men were mostly right-handed.