What causes some people to be left-handed, and why are fewer people left-handed than right-handed? Jun 21, 2004 Clare Porac, a professor of psychology at Pennsylvania State University who studies handedness, explains. Researchers who study human hand preference agree that the side of the preferred hand (right versus left) is produced by biological and, most likely, genetic causes. The two most widely published genetic theories of human hand preference argue that evolutionary natural selection produced a majority of individuals with speech and language control in the left hemisphere of the brain. Because the left hemisphere also controls the movements of the right hand--and notably the movements needed to produce written language--millennia of evolutionary development resulted in a population of humans that is biased genetically toward individuals with left hemisphere speech/language and right-hand preference. Approximately 85 percent of people are right-handed. These theories also try to explain the persistent and continuing presence of a left-handed minority (about 15 percent of humans).
Posted on: Fri, 18 Jul 2014 09:56:12 +0000
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