Re: I was looking at your web page about genetic handedness.

Dear Loraine,

Hello! Thanks for your question!

For a number of years, scientists have sought a biological explanation for handedness in humans. Why are so many more right-handed people than left- handed people? What determines whether someone is right- or left-handed? Although concrete numbers are not available because defining the criteria which classifies an individual as right- versus left-handed is difficult, the majority of humans (anywhere from 70 to 95%) are right-handed, while a smaller percentage (around 10 to 30%) are left-handed. Interestingly, humans seem to be the only primate species to exhibit a preference for one hand over the other. While some animals do display preferences for hand usage on an individual level, there does not seem to be a consensus among primate specialists that any non-human species exhibits a similar species- level handedness found in humans. The biological basis for handedness is poorly understood, and a number of theories have been proposed. If you are interested in the details, I refer you to the resources listed below. Basically, handedness does not seem to be governed by genetics alone. A number of developmental influences have been proposed, in addition to social and cultural factors.

In your question, you ask, how does one know if he or she is truly right- or left-handed? Well, the short answer is that we really do not know. There are a number of tests that can be done to try to determine an individual’s dominant side--for instance, not only which hand do they prefer to use, but which eye do they prefer, and which leg do they prefer. For example, to determine eye dominance you can sit with both eyes open and line up the tip of your finger, at arm’s length, with a distant object. Then, close each eye separately. The eye that results in the object and your finger remaining aligned is your dominant eye. Unfortunately, these kinds of tests are often difficult to interpret and are not always accurate. However, as I touched on earlier, it is likely the handedness is not solely a genetic phenomenon. There are probably many environmental factors that contribute to the development of right- versus left- handedness. Therefore, handedness is probably more a result of an individual’s exposure to influences in their surroundings rather than an inherent biological property. In other words, it is possible that one person may become right-handed when they mature in one environment, but may develop left-handed skills when raised in a different one.

As you mentioned, left-handed people have been discriminated against in the past. Although it seems that such prejudice has subsided, there are likely some remaining stigmas. (However, this is difficult for me to judge personally for I am right-handed.) In your question, you ask: what should you do? I am not really sure what you mean, but I imagine that you are concerned about your own handedness. My best advice is to not worry about it. Use the hand that you are accustomed to using, whether it is right or left. If you prefer to use your left hand, that is great! In contrast to the 1950’s, there are now a number of companies that specialize in manufacturing left-handed products. Through active scientific research, we can begin to understand the factors that contribute to human handedness. Hopefully, this, in turn, will further our awareness and appreciation for "lefties" such that there will never be a need for things like "hand- switching" again.

I hope you find this information helpful. I have listed a number of resources below. Please feel free to contact me with further questions!

Nikki
nmdavis@fas.harvard.edu

The Left Hand.com
This company sells a wide variety of left-handed products.

Creation of the Sinister: Biological Contributions to Left-handedness
This is an article by Monica Watkins from the Spring 1995 issue of The Harvard BRAIN, Harvard University’s undergraduate neuroscience magazine.

Gauche! Left-Handers in Society

Primate Handedness and Brain Lateralization Research
This is a website that describes the research of M. K. Holder, a scientist who studies handedness in humans and primates.

I also came upon a number of books that look interesting:

Left-hander syndrome: the causes and consequences of left-handedness , by Stanley Coren.

The Left-Hander’s Guide to Life, by Leigh W. Rutledge, Richard Donley (contributor), James Bennett (illustrator)

The World's Greatest Left-Handers: Why Left-Handers Are Just Plain Better Than Everybody Else, by James T. De Kay, Sandy Huffaker