So Why Are One-Tenth Of World’s Population Ciotacha.

Today, about one-tenth of the world’s population are left-handed [In Irish ‘ciotach’].
Why are such a small proportion of people left-handed, and why does the trait exist in the first place?

Daniel M. Abrams investigates how the uneven ratio of lefties and righties gives insight into a balance between competitive and co-operative pressures on human evolution.

A 1996 Belgian study found that left-handedness is about twice as common in about 21% of both fraternal and identical twins, than found in the general population.

According to a 2013 Yale University study, people who are left-handed are at greater risk of psychotic disorders such as schizophrenia. Researchers who polled patients at a mental-health clinic, found that 40% of those with schizophrenia or schizo-affective, wrote with their left hand; considerably higher than the 10% of lefties found in the world’s general population.