If It’s Sharp and Pointy, It’s Going on My Left Hand

by syaffolee

The first time I was conscious of handedness was probably in school during one of those art lessons when we were supposed to cut out stuff.  The teacher noticed I was using the right-handed scissors with my left hand so she made me exchange them for left-handed scissors.  The left-handed scissors felt really weird and in the end, I had a terrible time cutting things out of construction paper.  This may be me unconsciously mimicking my father–since he uses right-handed scissors with his left hand.  Left-handed scissors feel weird on my left hand.  Right-handed scissors feel weird on my right hand.  As for left-handed scissors on my right, er, no.  It only feels right when I use right-handed scissors on my left and that’s what I still use, even today.

I also throw things with my left hand.  If I’m not at some silly formal dinner, I use the knife with my left hand and the fork with my right (switching while you’re eating is too inefficient).  I use the pipetman with my left as well as the plate spreader.  When I clasp my hands, my left thumb is on top.  However, I write with my right hand.  Does this mean that I’m a natural lefty who has been forced to write with my right hand?  I don’t recall anyone forcing me to write with my right. So does that mean I’m ambidextrous?

In Right Hand, Left Hand, Chris McManus posits that there is no such thing as being ambidextrous.  Everyone is either strongly right-handed, strongly left-handed, weakly right-handed, or weakly left-handed.  There’s even a questionnaire to determine your handedness.  If you answer the questions equally with left and right, it only means that you need a more detailed questionnaire.  This, I think, is silly.  While having someone answer a million question survey may finally tease out whether someone is slightly biased to one side,  I don’t think that this will matter much to the real world outside of academia.

What’s most interesting about Right Hand, Left Hand is the overarching theory that McManus spins by pulling together various research in all sorts of disciplines in order to explain handedness in the universe.  The theory is this: because of the deep observed asymmetry in physics, one of the results is culture and civilization today.  Whoa, whoa, whoa, you might say–that’s a pretty big theory, one that on the face of it doesn’t wash.  Well, here’s his train of thought:

*Experimental particle physics has shown that the universe is asymmetrical. (Example: A Nobel prize winning experiment involving cobalt-60 contradicting the Law of Conservation of Parity)
*Perhaps the asymmetry of subatomic particles have led to the abundance of D-sugars and L-amino acids present in life.
*The L-amino acids determine the structure of proteins in a living body.  It’s been known, since about 2000, that there are cilia in the developing embryo that beat a certain way (perhaps due to the protein structure) and create a gradient of signaling molecules which cause our hearts to develop on the left side of our body.  This may also be under genetic control.  McManus speculates that a similar mechanism causes our brains to also develop asymmetrically.
*Because of asymmetrical brains, we all favor one side or another.  Since using the right hand is dominant among humans, this has led to many peculiar cultural developments such as using the right hand for one thing and the left hand for another, to develop peculiarities in language and associations to each side, and to equate right with good and left with bad.

Other than some particular cultural things which appear to have developed by chance (such as on which side of the road you drive on, the direction in which the hands of a clock turns, and from which way you start writing–i.e. left to right in English and right to left in Arabic), McManus’s theory sounds logical and presents a nice and pat explanation for how things came to be.  The only problem is, there’s no experimental evidence to prove that the next step is a consequence of the previous step.  No one has actually proven that the properties of subatomic particles drive the asymmetry of D-sugars and L-amino acids.  Much of the cultural dichotomies of left and right are anthropological speculations rather than direct consequences from brain asymmetry.  One assertion that McManus makes is that even though the notion of right=conservative and left=liberal stemmed from historical context, these associations would have been made regardless of what the French National Assembly did.  That it would have been inevitable.  At this point, I think he’s stretching his left and right associations, at best.

One thing I will note is that this book was published in 2002 so some of the information is out of date.  At the time of its publication, genes for handedness had yet to be discovered and the theory that cilia is a mechanism that causes our brains to develop asymmetrically was yet to be proved.  In 2007, researchers discovered the gene LRRTM1 which increases the likelihood of being left-handed.  In the same year, cilia were also found to be responsible for brain development.   So in this case, McManus’s predictions did end up being correct.

On the whole, I did enjoy Right Hand, Left Hand.  I think McManus has managed to collate a lot of the research, history, and trivia related to handedness into a coherent story that, although shaky on some of his speculations, is very readable for the curious layperson.