The Left-Handed Advantage

Feb. 17, 2005 — -- It's not easy being a lefty.

Statistics show left-handed people are more likely to be schizophrenic, alcoholic, delinquent, dyslexic, and have Crohn's disease and ulcerative colitis, as well as mental disabilities. They're also more likely to die young and get into accidents. So if evolutionary theory dictates survival of the fittest, why do lefties still exist?

According to new theories, what left-handed people (and other animals) may lack in fitness, they make up by being different.

Researchers in France recently took an interest in the disproportionately high number of left-handed athletes who thrive in sports involving direct one-on-one contact, such as baseball (think Babe Ruth), tennis (think John McEnroe) and boxing (think Oscar de la Hoya or the fictional Rocky Balboa).

Charlotte Faurie and Michel Raymond of the University of Montpellier in France figured the same reason so many left-handed people are successful in such sports could also explain a possible higher success rate among lefties in primitive combat.

This means that, back in the days when fighting was an important part of survival and winning mates, the rare left-hander may have come out on top more often.

Watch That Left Hook

Here's the thinking: Most left-handed people would be practiced in fighting right-handed people (since right-handed people make up the majority), while most right-handed fighters would not be as prepared to fight someone who favors their left side. Advantage: lefties.

"The fact that left-handers are less common means they have a surprise effect," said Faurie.

To prove their theory, Faurie and Raymond surveyed nine primitive societies in five separate continents. Through a mix of direct observation and existing data, they estimated the number of left-handed people within each population. They also looked at murder rates, thinking that those communities with higher murder rates might favor populations with more left-handed people. The more violence, the more chances lefties would have at issuing their unexpected left hook, or other such weapon, and come out on top.

Among these samples, they found strong support for the idea that, at least in primitive societies with higher levels of violence, lefties thrive.

For example, when they singled out the Dioula of Burkina Faso in West Africa, where the murder rate was only 0.013 murders per 1,000 residents each year, they found only 3.4 percent of the population were left-handers. Data from the Eipo of Indonesia, meanwhile, where there are three murders per 1,000 people each year, show 27 percent of the population is left-handed.

Other research is suggesting that humans aren't the only species who have minorities of certain side-favoring individuals. The equivalent of lefties has been observed in chimpanzees, toads, even among schools of fish.

Favoring one side -- a result of something called lateralization of the brain -- was once thought to be a uniquely human trait linked to language. The ability to speak comes mostly from left regions of the brain, so the assumption was this would correspond with increased motor control on the opposite, or right side. In motor control, activity on one side corresponds to the opposite side of the brain. So this could explain why about 70 percent to 90 percent of people are right-handed.

But lately, researchers who study animals have been poking holes in that idea.

William Hopkins, a psychologist at Emory University's Yerkes National Primate Research Center, has found most chimpanzees use their right hands for a number of functions, from throwing a ball to scooping peanut butter from a tube. Furthermore, he and his colleagues have linked this handedness to the KNOB, an area of the brain associated with motor activity, not language.

Hopkins further points out that chimps don't have language, so why would there be a majority of right-handed chimps? As among humans, being in a minority when it comes to handedness has its advantages.

"The advantage is at the individual level," said Giorgio Vallortigara, a psychologist at the University of Trieste in Italy. "The advantage is observed only until the minority group remains a minority. If the number of individuals that do not share the side preference that most do increases, then the advantage is lost."

Swimming Their Own Way

Vallortigara has studied how this works in certain schools of fish. Some fish swim in large groups, or shoals. Traveling in a pack provides individuals with extra protection from predators. Most of the fish in the group share the same tendency to keep an eye out on one side or the other for predators and to flee in a particular direction if a threat is seen.

Minority-sided fish, meanwhile, are likely to watch the other way and turn and flee in the opposite direction. While these fish miss out on the protection of the group, they gain the element of surprise -- predators don't expect them to turn in the opposite direction from the group.

Similar examples can be found among birds and toads. In each case individuals that favor an unusual side find some benefit, be it surprising predators with the direction of their flight or by finding resources that might elude the majority.

Still, researchers point out that, at least among humans, genetics is not the only factor behind left-handedness.

Evidence has shown a link between trauma during gestation or during birth, as well as in the age of the mother and so-called pathological left-handedness. Numbers show that mothers who are over 40 at the time of their child's birth are 128 percent more likely to have a left-handed baby than a woman in her 20s.

"Handedness is controlled by a whole lot of pathways in the brain and if any one of these pathways is mucked up during gestation, then handedness becomes a cosmic dice game," said Stanley Coren, a psychologist at the University of British Columbia and author of "The Left-Handed Syndrome." "We believe this accounts for about half of all left-handers."

It could be that this early trauma is also the trigger behind health problems linked to left-handedness. Coren points to two famous left-handers, Presidents Bill Clinton and George H.W. Bush, as evidence. Both had histories of birth stress and have health issues from Clinton's severe allergies to Bush's Graves' disease.

Then again, as many lefties might point out, being left-handed can also offer intellectual prowess. Tests conducted by Alan Searleman from St Lawrence University in New York found there were more left-handed people with IQs over 140 than right-handed people. Famous left-handed thinkers in history from Albert Einstein to Isaac Newton to Benjamin Franklin seem to underline the point.

As Hopkins says, it may be that left-handed people occupy the extremes when it comes to health and ability.

"The anomaly is left-handed people make up the extremely gifted and the extremely compromised," said Hopkins. "The rest of us make up the middle ground."