Handedness is a better (faster or more precise) performance or individual preference for use of a hand, known as the dominant hand; the less capable or less preferred hand is called the nondominant hand. Despite the common terminology of “left-handed” or “right-handed”, handedness is not a discrete variable (right or left), but a continuous one that can be expressed at levels between strong left and strong right. In between these extremes lie various degrees of mixed-handedness and ambidexterity. Men are somewhat more likely to express a strongly dominant left hand than women. Studies suggest that 88–92% of the world population is right-handed.
Right-handedness is most common. Right-handed people are more skillful with their right hands when performing tasks. Studies suggest that 88–92% of the world population is right-handed.
Left-handedness is far less common than right-handedness. Left-handed people are more skillful with their left hands when performing tasks. Studies suggest that approximately 11% of the world population is left-handed.
Cross-dominance or Mixed-handedness is the change of hand preference between tasks. This is common in the population with about a 1% prevalence.
Ambidexterity is exceptionally rare, although it can be learned. A truly ambidextrous person is able to do any task equally well with either hand. Those who learn it still tend to favor their originally dominant hand.
Scientists aren’t exactly sure why some people are left-handed, but they know that genes are responsible about 25% of the time. Left-handedness does tend to run in families. In fact, identical twins, who share the same genes, can sometimes have different dominant hands. There are plenty of theories on what else might determine which hand you write with, but many experts believe that it’s kind of random.
Studies indicate that left-handedness is more common in males than females.
Now, lefties make up about 11% of the population.
Society tends to associate the left side of something with the bad (“two left feet”), and the right side with the good (“my right-hand man”). But if you’re left-handed, you might not think the same way as righties.
People who are left-handed are at greater risk of psychotic disorders such as schizophrenia, according to a 2013 Yale University study. When researchers polled patients at a mental-health clinic, 40% of those with schizophrenia or schizoaffective said they wrote with their left hand; that’s considerably higher than the 10% of lefties found in the general population. Studies have also found links between non-right-handedness and dyslexia, attention deficit hyperactivity disorder, and some mood disorders.
There’s one thing that most handedness experts can agree on: lefties have the upper hand (pun intended) when it comes to one-on-one sports like tennis, boxing, and pitching a baseball.
International Left-Handers Day is held annually every August 13. It was founded by the Left-Handers Club in 1992.
Of all the interesting facts about handedness, probably the most important one, is that it doesn’t matter much at all. The differences between righties and lefties are really rather subtle, and of much greater scientific interest than any kind of practical use.