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In any given population, about ten percent of the people are left-handed and this figure remains relatively stable over time. So-called "handedness" runs in families, but what causes it and why the proportion of left-handed to right-handed people is a constant are still a mystery. One thing we do know is that hand dominance is related to brain asymmetry; and it seems to be generally agreed that the human brain is profoundly asymmetric, and that understanding how this works will tell us much about who we are and how our brains work. Brain[function] is distributed into the left and right hemispheres, and this is crucial for understanding language, thought, memory, and perhaps even creativity. For right-handed people, language activity is mainly on the left side. Many left-handers also have left-side language dominance, but asignificant number may have language either more evenly distributed in both hemispheres or else predominantly on the right side of the brain. Because left-handedness is seen as a key to the complex anatomy of the brain, scientists are searching for links to other conditions, including immune disorders, learning disabilities, and reduced life expectancy.
