Why Are Some People Left Handed & Others Right?

About 85 percent of the world is right-handed. Of the remaining 15 percent, most are left-handed with a small number, about one in 100, being ambidextrous or able to use either hand to some extent. The leading theories on why deal with the body and genetics, but there is not enough evidence yet to answer the question definitively.

Old Theories

• Left-handedness used to be a seen as a curse, a sign of wickedness or brain damage. Even in the early to mid 20th century, natural left-handers were taught to use their right hand anyway. Such theories have since been dismissed by the scientific community.

Genetics

• The leading theories regarding why some people are right or left handed have to do with genetics. Geneticists believe that natural selection and human activities over time have favored the gene for right handedness. They attribute the difference to two different manifestations of a gene. The D gene produces right-handers, and the C gene produces both. C stands for "chance." Some people with the C gene are right-handers, some are left-handers and some are ambidextrous.

Biology

• The biological theory relies on the different abilities of different areas of the brain. It states that because speech and language both require fine motor skills that the brain might divide itself in such a way that one side of the brain handled both. Because the left side of the brain handles language in most people most people would be right-handed. Others argue that because some people do use the right hemisphere for language this theory wouldn't explain why there are so few left-handers.

The Shield

• Some have put forward the idea that left-handedness relates to where a warrior holds his shield. Because the heart is on the left side of the body a warrior who held his shield with his left hand would be better protected. Others point out though that according to cave paintings, right-handers were dominant before humans started using shields.

Injuries and Learning

• For many years, people who were left-handed were trained to be right-handed anyway. This isn't done anymore in most of the world; however people who suffer some type of injury or have a disability in one hand frequently learn to use the other just as efficiently.

Creativity

• Some have claimed that left-handers are more creative than right-handers, pointing to a long list of famous left handers including Leonardo Da Vinci and Albert Einstein as examples. If this were true it might help lead to answers. Critics, however, point out that there are are also many right-handed creative people and that there are many photos showing Einstein drawing on a chalkboard with his right hand.