One of these alleles is a D gene (for dextral, meaning ¿right¿) and the other allele is a C gene (for ¿chance¿). The genetic proposal to explain hand preference states that there are two alleles, or two manifestations of a gene at the same genetic location, that are associated with handedness.
These theories also try to explain the persistent and continuing presence of a left-handed minority (about 15 percent of humans). Approximately 85 percent of people are right-handed. 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. 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. 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.
Clare Porac, a professor of psychology at Pennsylvania State University who studies handedness, explains.
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