As humans, the way that our hand preference is determined is still mysterious to the scientific world. Even more baffling is the reason why the human species has a 90% right-handed majority. In fact, we are the only species with any, let alone a huge difference in laterality. All other animals are more or less 50-50 when it comes to righties and lefties (Wolman 46); and yes, animals can be left or right-pawed, finned, winged, or “tentacled.”
Argument as to the origins of hand preference seems to come done to nature vs. nurture. While handedness can be heavily influenced by the environment, to the point where people are actually forced to use a certain hand, it seems to me that there is more of an argument on the genetics side of this. In David Wolman’s book, A Left-Hand Turn Around the World, he writes, “genetics isn’t as linear as we’d like to think.” It’s not as though we have a separate, specific gene for each and every characteristic of our complicated little bodies. In a far more concise way than I could ever dream of describing this, Wolman writes:
“Traits can result from single genes, various combinations or committees of genes, genes that change the probability of other genes switching on or off, or genes that change the biochemistry of a developing organism in some profoundly subtle way that science can’t yet detect” (48).
Only a very small portion of the human genome—or the “human cookbook,” as Wolman calls it—itself has been mapped out and understood, and handedness just happens to be another part that is left to be deciphered. About this, Richard Palmer from the University of Alberta said, “The amount that we know with confidence about human handedness is so pitiful it’s almost shocking” (48). So in other words, it’s very complicated.
As thus far and as I said before, I think that hand preference is most likely the result of genetics, and Wolman’s book includes some convincing statistics about probabilities of hand preference in children to support that:
- two right-handed parents have a 9.5% probability of having a child who is left handed
- one right-handed parent and one left-handed parent have a 19.5% probability of producing a left-handed child
- two left-handed parents have a 26.1% probability of producing a left-handed child
It’s not exactly a smoking gun, but hey—it’s something.
Wolman also talked about a study done at Purdue University, in which various plants “refused to inherit a mutant gene” from the parent plants (45). I found this very interesting, because if left-handedness is a mutant form of a gene, perhaps only some people are able to inherit it, only the 10% left-handed portion of the population to be precise. This is a possibility for the major difference in the numbers of righties and lefties.
One last thing I wanted to get to was the “Right Shift Theory,” created by English researcher, Marian Annett, who apparently “doesn’t take lightly to puppet jokes. . . .” While I have some more to learn about this, Marian’s basic idea is about the complexity and asymmetry of the human brain, which allows us to be the only species to have evolved speech and possibly why, as a population, we have a tendency to be right handed. The speech center of the brain is housed in the left hemisphere, which controls the right side of the body. For some magical reason which I have not yet grasped, this encourages our right-handed bias.
What I was most concerned about in regards to Miss Annett, however, was her idea for handedness to exist on a continuum. Now remember that little thing I was so excited about, and called a “Laterality Slider Chart” that I created and explained in my last post? Well, it turn out it has been done before. Even though I didn’t call it a “continuum,” that’s exactly what I was thinking about, and I thought of it before I read about hers. And I actually made a chart for mine. So there. In all seriousness though, I’m sure my idea was like a snowflake on an ice berg in compared to Marian Annett’s. I’m excited to learn more about what she has to say in her paper, Handedness and Cerebral Dominance.
What’s YOUR handedness? Take the poll at the bottom of my first post!
Source:
Wolman, David. A Left-Hand Turn Around the World: Chasing the Mystery and Meaning of All Things Southpaw. NewYork: Da Capo Press, 2005. Print.
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