ON THE LEFT HAND, THERE ARE NO EASY ANSWERS:

"Humans are asymmetric animals. Early in our embryonic development, the heart turns to the left. The liver develops on the right. The left and right lungs have distinct structure.  There are certain rare syndromes in which the usual asymmetry of organs is reversed."  Hand dominence is related to brain asymmetry.  For right-handed people, language activity is predominantly on the left side. Many left-handers also have left-side language dominance, but a significant number have language either more evenly distributed in both hemispheres or else predominantly on the right side of the brain.  In general,  left-handers have less asymmetric brains, with more even distribution over the two hemispheres.  Since left-handedness has been the key to the complex anatomy of the brain, they continue to look for links to many other conditions.