Left-handedness appears to be associated with a greater risk for a number of psychiatric and developmental disorders. While lefties make up about 10% of the overall population, about 20% of people with schizophrenia are lefties, for example. Links between left-handedness and dyslexia, ADHD and some mood disorders have also been reported in research studies.
What is scarier still, especially for me, is that those of us who are cross-dominant, what the article calls "mixed-handed," represent only 1% of the population but a disproportionately high percentage of those suffering from serious psychological disorders. (Please, no one tell Occupiers that I am part of the 1%.)
Setting aside, reluctantly, the impulse of every left-handed or cross-dominant person to read this article and go on a paranoid journey of self-diagnosis, the studies cited in the Wall Street Journal offer a number of interesting areas for further thought. The first is in the suggestion that handedness may actually have more to do with environment (particularly the pre-natal environment) than genetics. This undermines the default excuse, fed to me as a child, that some people are just born left-handed or that it makes someone "special." In fact, only about 25% of the matter of handedness is decided by genetics. In reality, left-handedness is more likely to be the result of a hostile pre-natal environment. "Babies born to older mothers or at a lower birth weight are more likely to be lefties, for example. And mothers who were exposed to unusually high levels of stress during pregnancy are more likely to give birth to a left-handed child." Far from being "special," a more honest rhetoric might describe southpaws as "defective" (not that "special" hasn't already become societies euphemism for that anyway). Being left-handed is less a pleasant genetic rarity like being born with hazel eyes and more like being born with a lazy eye (or, in the case of us poor, unfortunate cross-dominants, being born cross-eyed).
Related to this, and more nearly related to my earlier point about personality theories, the relationship between handedness and mental disorders speaks to the actual relevance of brain lateralization. As has long been suspected, left-handed people show a greater tendency toward right-brain dominance, with some 30% of left-handed people being either right-brain dominant or "distributed." It is this deviation from the standard pattern of lateralization which many scientists believe may contribute to higher incidences of schizophrenia and other disorders, in addition to more mundane problems like difficulty in school (which may explain why left-handed people are paid 10% less than their right-handed colleagues).
This is obviously not intended to endorse some kind of fatalism about left-handedness or mixed-handedness. The article points out that many highly successful people have been left-handed, including six of the last twelve United States presidents. These facts should, however, affect the way that we understand handedness and, as the article specifically suggests, should make parents of left-handed or cross-dominant children more aware of potential risk factors associated with being left-handed.