Some people are left-handed primarily due to biological and genetic factors that influence brain asymmetry, the way the two hemispheres of the brain specialize in control and function. Evolutionary biology suggests that most people have language and motor control in the left hemisphere of their brain, which controls the right hand, leading to a majority of right-handed individuals. About 10 to 15 percent of people are left-handed because of different genetic variations and brain development patterns that cause the right hemisphere to dominate in motor control for the left hand. Genetically, handedness is influenced by multiple genes rather than a single gene, possibly up to 40 different genes involved in right-left asymmetry and brain development. Some rare genetic variants have been identified that are more common in left-handed people. Hand preference may also arise randomly due to developmental variations during embryonic brain development. Environmental influences and chance also play roles. Additionally, evolutionary theories suggest that left-handedness persists at a low frequency because it can provide a strategic advantage in certain social or combat situations, but it is balanced by evolutionary costs that keep it as a minority trait. In summary, handedness is a complex trait influenced by genetics, brain asymmetry, developmental factors, and evolutionary dynamics, with left- handedness occurring due to a mix of these biological influences and a degree of randomness.
