At first sight it seems a fairly simple matter to say what is meant by being right-handed or left-handed, but a little consideration soon shows that this very simplicity is a source of difficulty. We say that a person is right-handed if he for preference uses his right hand rather than his left to carry out the more skilled kinds of movement and is more skillful at such movements with his right hand than with his left. The converse is true of a left-handed person. Handedness, therefore, is nothing absolute; it is a question of degree, a preference based upon a skill with which the two hands are used. Moreover, it takes no account of the actual degree of skill present, nor does it imply any cause for the difference.
Left‐handedness occurs in about 8% of the human population. It runs in families and an adoption study suggests a genetic rather than an environmental origin. Since prehistoric times, left-handed individuals have been ubiquitous in human populations, exhibiting geographical frequency variations. Evolutionary explanations have been proposed for the persistence of the handedness polymorphism. Left-handedness could be favored by negative frequency-dependent selection. Data have suggested that left-handedness, as the rare hand preference, could represent an important strategic advantage in fighting interactions. However, the fact that left-handedness occurs at a low frequency indicates that some evolutionary costs could be associated with left-handedness. Overall, the evolutionary dynamics of this polymorphism are not fully understood. So, it might come as a surprise to some that the first genetic markers associated with imparting the left handed gene have now been discovered.