Dispelling the myth of the left-handed genius

Ordained at birth.
Ordained at birth.
Image: Reuters/Thomas Peter
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Ask left-handed people about their lot and they’ll probably tell you how special they are. They will list all of the famous and brilliant people who are left-hand dominant including every post-Cold War president (except George W. Bush), Joan of Arc and Michelangelo to name just a few.

Up until recently, in America and still in some Asian countries, lefties were vilified. They’ve been accused of being sociopaths and forced to use their right hand.

More recently, we’ve come to celebrate lefties as iconoclasts. The new narrative stresses that lefties’ brains work differently, which makes them more creative. When exposed to language, lefties are more likely to engage both sides of their brain, rather than just the left side. It has also been said that using your left hand engages the right side of the brain, which is associated with creativity. A recent blog post in the New Yorker points to several studies demonstrating how much smarter and more creative lefties are.

Though how the brain works is still not well understood, and the right brain/creative and left brain/rational distinctions are really not so simple. Dr. Daniel Geschwind, a professor of human genetics, neurology and psychiatry at University of California, Los Angeles, School of Medicine has observed that lefties are disproportionately in extraordinary jobs—they make up only 10% of the population, but account for 25% of math professors at MIT. They may be over-represented in professions like mathematics professors because they have a comparative disadvantage in language. They do think and relate to language differently, but why exactly isn’t well understood. “We observe it and know it’s there, but we don’t know why exactly,” he says.

We may never understand the intricacies of the human brain but we can observe cold and objective economic data.

That data show it doesn’t pay to be a left-handed. According to research by Harvard economist Josh Goodman (pdf), lefties earn 6% less than righties. He attributes the gap to differences in cognitive skills, education, and occupational choices. He found that lefties are more likely to have learning disabilities and behavioral problems. Goodman looked at data from the US and the UK that tracked the lives of several different age groups, between 11% and 13% of the population are lefties, similar to estimates that about 10% of the population is left-handed. In addition to tracking the education and income of the respondents, the surveys administered tests on intelligence. Goodman measured the distribution of cognitive ability by handedness. In all but one of the cohorts, in both countries, lefties are more likely to be in the lower end of the cogitative skill distribution, which means less ability. Lefties are also rarely on the upper end of the distribution (amongst the smartest respondents), debunking the mad genius myth. He found lefties have worse language and math skills than their right-handed counterparts. Goodman’s estimates show that lefties and righties are equally likely to finish high school, but lefties are about 2.5% less likely to have a college degree.  That may explain why lefties typically work in lower paid occupations. Also contrary to stereotype, lefties are less likely to work in creative fields.

Why is this? Goodman found a correlation between low-birth rate (suggesting trauma in-utero) and left-handedness. One Danish study found that mothers who experience severe stress during the third trimester were more than three times more likely to have mixed-handed children. This suggests that for some people, being left-handed indicates pre-birth neurological damage.

There are two types of lefties: environmental lefties, who are left-handed because of a traumatic in-utero experience, (handedness is determined before birth) and genetic lefties, who came from a perfectly healthy pregnancy and their left-handedness is in their DNA. Scientists at Oxford University claim to have identified a left-handed gene.  It’s difficult to separate two populations with exact precision.  When Goodman identified genetic lefties by having a left-handed mother, just under 20% of his lefties were genetic. Geschwind has also observed that being left-handed might indicate in-utero neurological damage, but that is simply because there are so few lefties to begin with. Throughout history lefties have consistently made up 10% of the population. Probably some genetic lefties had a traumatic pregnancy and became righties, but because there are so many righties to begin with, they make up a smaller share of the rightie population.

Once Goodman separates environmental and genetic lefties his results change. There is little, if any, difference in earnings or cognitive ability between righties and genetic lefties. It makes sense then that previous studies and urban legend labeled lefties as either geniuses or total degenerates. Being left-handed can signal a brain impairment, which means a larger fraction of that population will have a cognitive disadvantage. Goodman points out that most previous studies had a small or biased sample, which explains the strong and conflicting characterizations of lefties.