The Mystery Of Handedness

This morning I woke up and, as I do first thing every morning, I reached over to the end table to retrieve my glasses. Of course, I used my right hand to pick them up and put them on — just as I use my right hand to do just about everything, without a conscious thought.

Like the vast majority of humans, I’ve got a dominant hand. A pen goes naturally into my right hand, and I can produce somewhat legible handwriting with it. Trying to pick up and use a pen with my left hand feels incredibly weird, and I can’t write anything with it. The same holds true for throwing a ball, or using a towel to wipe down the kitchen counter. The right hand does the lion’s share of the work; the left hand helps from time to time by, say, doing its share of keyboarding and holding an object the right hand is working on.

Somewhere between 85 and 90 percent of humans are right-handed, between 10 and 15 are left-handed, and a tiny fraction are ambidextrous (able to use either hand with equal ease) or mixed-handed (preferring to use the right hand for some tasks and the left hand for others). Why is that so, as opposed to a world where every human can use either hand at their whim? What causes “handedness”?

Scientists and researchers don’t really know for sure. The current thinking is that handedness is the product of both genetics and environment, and maybe some other factors, too. Scientists believe that at least part of hand preference can be traced to brain activity, with the right half of the brain controlling the left half of the body and the left half of the brain controlling the right half of the body. Hand dominance is related in some way to our brain hemispheres. But nobody has determined conclusively whether the brain set-up of different people causes their handedness, or whether an innate hand preference, expressed from the earliest days of life, causes the brain to become wired and developed in a certain way. There also appears to be a genetic cause for hand preference, which is why left-handedness is more common in some families than others. (In my family, Grandpa Neal, UJ, and Richard are all lefties.) And it’s also clear that training and practice can play a role in developing more “even-handedness”; long-time baseball fans are familiar with the story of Mickey Mantle’s father drilling him on using both hands because he believed switch-hitters were more valuable than batters who could only swing from one side of home plate.

I find it fascinating that something as basic to the human condition as handedness remains shrouded in mystery, resisting the best efforts of scientists, geneticists, and behavioral psychologists to figure out why it happens. It reaffirms that we’re all pretty complex organisms, and there’s still a lot about homo sapiens that remains to be discovered.

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