For much of its history, the field of neuropsychology strived to understand what was wrong with the human species' left-handed minority. This effort was eventually abandoned after two key insights emerged. First, experts realized that handedness has a genetic basis, and any attempts to change it can have deleterious developmental consequences. Second, we learned that left-handers have remained a stable 10 to 15 percent of the human population for thousands of years: if lefties were truly weaker in some way, their numbers would have dwindled over time.

Still, people continue to question whether lefties are more vulnerable to physical and psychological maladies, despite only shaky evidence to support such claims. A well-publicized study in the early 1990s, for instance, reported that lefties had shorter life spans than righties, but those results have since been discredited. Subsequent research found no meaningful differences in mortality rates.

Likewise, very little evidence indicates that lefties are more likely to develop physical ailments. Some highly speculative research suggests that left-handers may be at a greater risk for restless legs syndrome and asthma, but other investigations report that left-handers face a lower risk for chronic obstructive pulmonary disease and pneumonia. Some researchers have proposed a tenuous association between handedness and the risk of schizophrenia as well as creative thinking. Studies suggest that significantly fewer people who consistently use their right hand develop schizophrenia, compared with left- or inconsistent-handers, who use their nondominant hand for common activities. But this observation lacks a causal explanation.

Because most equipment is built for right-handers, it is possible that left-handers are more prone to physical injuries at work or accidents while driving. Studies also show, though, that left-handed professional athletes may have an advantage over their right-handed peers because their movements are less predictable. In summary, handedness may influence certain behaviors or risks for specific disorders, but the evidence to date does not definitively support or convincingly account for these links.

Question submitted by Kevin McElroy via e-mail

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