Handedness

A person's preference for one hand when performing manual tasks.

The term handedness describes a characteristic form of specialization whereby a person by preference uses one hand for clearly identified activities, such as writing. For example, a person who uses his or her right hand for activities requiring skill and coordination (e.g., writing, drawing, cutting) is defined as right-handed. Roughly 90% of humans are right-handed. Because left-handed people who are forced to write with their right hand sometimes develop the ability to write with both hands, the term ambidexterity is often used in everyday parlance to denote balanced handedness.

An often misunderstood phenomenon, handedness is a result of the human brain's unique development. While the human mind is intuitively understood as a single entity, research in brain physiology and anatomy has demonstrated that various areas of the brain control different mental aptitudes, and that the physiological structure of the brain affects our mental functions. The brain's fundamental structure is dual (there are two cerebral hemispheres), and this duality is an essential quality of the human body. Generally speaking, each hemisphere is connected to sensory receptors on the opposite side of the body. In other words, the right hand is controlled by the left hemisphere of the cerebral cortex. When scientists started studying the brain's anatomy, they learned that the two hemispheres are not identical. In fact, the French physician and anthropologist Pierre Broca (1824-1880) and the German neurologist and psychiatrist Carl Wernicke (1848-1905) produced empirical evidence that important language centers were located in the left hemisphere. Since Broca's findings were based on right-handed subjects, and since right-handedness is predominant in humans, psychologists felt prompted to develop the notion of the left hemisphere as the dominant part of the brain. Furthermore, Broca formulated a general rule stating that the language hemisphere is always opposite of a person's preferred side. In other words, the left hemisphere always controls a right-handed person's language abilities. According to Broca rule's, left-handedness would indicate a hemispheric switch. Handedness research, however, uncovered a far more complex situation. While Broca's rule works for right-handers, left-handed people present a rather puzzling picture. Namely, researchers have discovered that only about two out of 10 left-handers follow Broca's rule. In other words, most left-handed people violate Broca's rule by having their language center in the left hemisphere. Furthermore, the idea of clearly defined cerebral dominance seems compromised by the fact that some 70% of left-handed people have bilateral hemispheric control of language.

While hemispheric dominance can be observed in animals, only humans have a clearly defined type of dominance. In other words, while animals may be right or left "pawed," only humans are predominantly right-handed. The American developmental psychologist Arnold Gesell (1880-1961), known for his pioneering work in scientific observation of child behavior, noted that as early as the age of four weeks infants display signs of handedness. At that age, according to Gesell, right-handed children assume a "fencing" position, right arm and hand extended; by the age of one, right-handedness is clearly established, the child using the right hand for a variety of operations, and the left for holding and gripping. Predominant right-handedness in humans has led researchers to define right-handedness as genetically coded. If left-handedness also had a genetic basis, was it possible to establish inheritance patterns? However, empirical studies, even studies of identical twins, have failed to establish left-handedness as a genetic trait. For example, a person with two left-handed parents has only a 35% chance of being left-handed.

In the past, left-handedness was associated with mental deficiency, as well as emotional and behavioral problems, which led to the popular belief, strengthened by folklore, that left-handed people were somehow flawed. In addition, left-handedness has also been associated with immunological problems and a shorter life span. While not devoid of any foundation, these ideas are based on inconclusive, and sometimes even deceptive, evidence. For example, statistics may indicate a shorter life-span for left-handers, but what statistics omit is the fact that higher mortality should probably be attributed to accidents in an often dangerous right-hand world.

An even greater challenge than right-handed scissors and can openers is what psychologist Stanley Coren calls "handism," the belief that right-handedness is "better" than left-handedness. The idea that left-handers need to conform to a dominant standard has traditionally been translated into punitive educational practices whereby left-handed children were physically forced to write with their right hand. While there is a growing awareness among educators and parents that left-handedness should not be suppressed, the left-handed child is still exposed to a variety of pressures, some subtle, some crude, to conform. These pressures are reinforced by a tradition of maligning left-handed people. Major religious traditions, such as Christianity, Buddhism, and Islam, have described left-handedness in negative terms. Current language is also a rich repository of recorded animosity toward left-handers. For example, the word left evolved from the Anglo-Saxon lyft, which means weak. The Latin word sinister, meaning left and unfavorable, is still used to denote something evil, and gauche, the French word for left, generally indicates awkwardness. The numerous expressions which imply that left is the opposite of good include a left-handed compliment.