On the Other Hand

Sep 4, 2014

By Bob Grant

 

With almost complete certainty, I can predict that you, dear reader, are right-handed. If I were a betting man, I’d put money on it. I’d make the same bet if you were reading this in India or Iowa, Kansas or Kathmandu. And a hundred years from now, I’d make the same bet again.

I can be so sure of myself not because I am some prodigious prognosticator, but because about 90 percent of humans are right-handed. That phenotypic ratio—nine right-handed people for every lefty—is relatively stable, not just across cultures and geographic regions, but perhaps across the span of human evolution. The archaeological record suggests that hominins were predominantly right-handed as far back as 2 million years ago,1 and a 2010 study of the wear patterns on 32,000-year-old Neanderthal teeth found that this extinct cousin of Homo sapiens was likely about 88 percent right-handed.2 It’s a ratio that has baffled scientists for more than a century, despite the fact that handedness is immediately familiar to everyone who uses their limbs. “We understand handedness, because it’s easy to say which hand you use for writing,” says Silvia Paracchini, a geneticist at the University of St. Andrews in the U.K. who is searching for genes that underpin human handedness. “But the reality is that we know very little about it. We cannot explain it with data.” Scientists are unsure how or why humans are so strongly biased toward right-handedness. What are the biological underpinnings of the behavioral asymmetry? Is this overwhelming dominance of righties reinforced by culture, or is it strictly a product of genetics?

Recently, some of the most interesting findings have come not from studying handedness in humans, but from observing the behaviors and brains of other animals. Once considered to be a uniquely human trait, handedness may exist on the individual level in other species, and may be common in primates. At the population level, some primate groups even appear to show biases toward one side or the other. A 2011 study involving nearly 800 great apes conducted by Emory University neuroscientist Bill Hopkins and colleagues found that for a particular bimanual task—which necessitates the use of both hands, one dominant and one supportive—gorillas, chimps, and bonobos tend to be right-handed, while orangutans showed a population-wide preference for using the left hand.3 And in 2012, Hopkins and collaborators in China found that a population of wild Sichuan snub-nosed monkeys (Rhinopithecus roxellana) is predominantly left-handed (about 70/30) for the same bimanual task.4

By far the most biased species is Homo sapiens, and some investigators hold firm that a consistent and overwhelming handedness bias to the right is a uniquely human attribute, much like language and other higher cognitive functions. Handedness, they say, likely stems from consistently reinforced cultural norms, and any reported biases toward one side of the body in nonhuman animals are primarily the result of experimental or observational artifacts or statistical error.

But in the past couple of decades, Hopkins and his collaborators have provided strong evidence that chimps do favor one side of their bodies over the other. The captive chimp colonies that Hopkins studies are 60 percent to 70 percent right-handed, regardless of the proportion of individuals in each colony that were human-reared,5 and recent scans of the chimps’ brains reveal corresponding brain asymmetries—hallmarks linked to hand preferences in the highly complex human brain. “I think the chimps offer an interesting comparison, because—biologically, genetically, cognitively, and anatomically—they show a lot of homologies to humans,” says Hopkins.

28 comments on “On the Other Hand

  • How fascinating! I’m mostly right-handed, but I use my left hand for writing. That’s useful for computer/mouse purposes, but not much else. It used to be really annoying when writing cheques as the stubs were always on the wrong side of the book. I’m also useless at calligraphy as I would need to write backwards to avoid smudging the ink with my hand! That said, I know a couple of brilliant graphic designers who are left handed, so it’s one of those topics that will continue to fascinate and it would be good to think a full explanation might eventually be discovered.



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  • CumbriaSmithy Sep 4, 2014 at 3:59 pm

    How fascinating! I’m mostly right-handed, but I use my left hand for writing. That’s useful for computer/mouse purposes, but not much else.

    That’s interesting Smithy! I am right-hand dominant, but partly ambidextrous.

    When I was using two computer systems, I settled for using the Acorn three-button mouse, with my left hand, and the Microsoft two-button mouse with my right, so as to confusing the actions.

    In sporting activities, such as table tennis, opponents find it confusing that I can use a bat in either hand – (although my right is slightly better).



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  • I had a teacher who could, after breaking a stick of chalk in two, write both halves of a sentence simultaneously, using both hands, with the first half on the blackboard above the second half.

    It would stop a rowdy class dead in its tracks, and was his standard trick for restoring order.



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  • Hi CumbriaSmithy. I thought the article really interesting as well. I’m surprised that the incidence is only one in ten as I would have thought it higher. In each class there would usually be quite a few left-handers who needed to be seated in a particular arrangement.
    I always assumed that all mammals would show a preference for one side. On occasion I’d study our pets to see whether they favoured left or right. I usually came to a conclusion as well, which probably just serves to demonstrate confirmation bias in action.
    One explanation I was given ( by a highly questionable source, I might add), was that the left-hander was the result of twinning in utero. The right-handed identical twin subsequently perished, leaving its mirror image in place. I don’t know if there’s any truth in this whatsoever, but it always struck me as a plausible explanation.



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  • In sporting activities, such as table tennis, opponents find it
    confusing that I can use a bat in either hand – (although my right is
    slightly better).

    I used to try to show off at snooker, having the ability to shoot just as well with either hand/arm. However, both sides were equally ‘average’, so I eventually gave up that particular sport!



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  • I’ve always thought handedness was hereditary. My mother was left-handed and my sister is too. My brother is right-handed, having – so I thought – inherited our father’s right-handedness. However, if it really was genetic, surely we ought to see a 50-50 split, not a 90-10.



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  • I can remember an article in New Scientist, (which I am trying to reference) that speculated that right handedness goes back to our evolutionary past, to the fish and birds. In a shoal of fish or a flock of birds, as the pack turns, most of the pack follow the turn, but a small percentage go the other way. The article thought this might be a strategy to confuse the predator. If everyone turned right at the same time, the predator could predict. But if a few turned left, it would add to uncertainty for the predator. The same is set to apply to herd animals like Zebra on the Serengeti plains.

    However this is at odds with the above observations because if it went back this far in evolution, I would expect it to be consistent across primates and most animals.



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  • How many left-handed kids were forced to learn writing using their right hand, either for convention and/or religion (the devil’s tool)?

    I believe tying the left arm behind a child’s back was customary. It’s not nice to fool with mother nature.



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  • I was ambidextrous as a child, writing and drawing with whichever hand I felt like at the time. When I started school, the teacher made me choose a hand. (I’m predominantly right handed now.)

    Pissed my dad right off.

    I always did weird things like if playing base ball, I would bat right handed, but if playing hockey, would use a left handed stck.



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  • I am a lefty, and I feed with my left hand when using a knife and fork, as do a majority of other lefties. What puzzles me is why most right handers also hold the fork in their left hand – I think they have got it wrong!



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  • I’m strongly left-handed and would be much more interested in articles about why it has persisted in the human population in spite of open persecution (okay, that’s an emotional word, but you know what I mean) in many cultures. I wonder if any studies have been done on the frequency of left-handedness in certain minority populations. (convicts, artists, religious clerics, depressives, pilots, Nobel Prize winners, polyglots, mass murderers, etc.) Surely there are cerebral ramifications to the reversal of (normal) hand preference in a species.



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  • Urn Sep 4, 2014 at 10:13 pm

    I always did weird things like if playing base ball, I would bat right handed, but if playing hockey, would use a left handed stick.

    In sports as with my Table-Tennis example, anything close up needing sharp vision, requires the dominant use of the opposite eye.
    It is therefore a disadvantage to use the opposite hand unless it can be co-ordinated with the opposite eye!

    The reason it confuses opponents making snap decisions in table tennis, is that mirror image actions with the opposite hand, impart the reverse spin and change the reach on that side!



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  • I’m a lefty myself, and would be curious about what populations are lefties as well. I’m a creative type (artist, writer, singer, etc) but never really researched the numbers on how many of my ilk are the same.

    While I do enjoy being the 1 in 9 it does make me wonder what causes such proclivities and the article only seems to be touching the surface.



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  • One interesting feature in the design of castles, was that narrow spiral staircases always twisted in the same direction, allowing a defender at the top to swing a sword, while a right-hander coming up the stairs, was obstructed by the central supporting stone pillar.

    Left handed attackers could of course swing their swords while going up stairs, so were highly prized as attacking warriors in castle sieges.



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  • CumbriaSmithy Sep 4, 2014 at 6:51 pm

    However, if it really was genetic, surely we ought to see a 50-50 split, not a 90-10.

    There is an explanation of a genetic theory here:

    http://www.scientificamerican.com/article/what-causes-some-people-t/

    The proposed genetic locus that determines hand preference contains an allele from each parent, and the various possible genetic combinations are DD individuals who are strongly right-handed, DC individuals who are also mostly right-handed, and CC individuals who are either right-handed or left-handed. These genetic combinations leave us with an overwhelming majority of human right-handers and a small, but persistently occurring, minority of left-handers.



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  • 21
    Elizabeth says:

    At my Scottish primary school, the three Kerrs in my class were left-handed, and “kerry-handed” was a local term for “left-handed”.

    Having said that, it is not uncommon for identical twins to have opposite handedness – there’s even a name for it: “enantiomorphic twins”. Sometimes their brains have opposite lateralisation for language, and sometimes even their hearts are on opposite sides. So there are strong non-genetic factors.



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  • . Elizabeth. Having said that, it is not uncommon for identical twins to have opposite handedness – there’s even a name for it: “enantiomorphic twins”.

    That seems to add credence to my suggestion above ( that is; the left hander is the remaining twin).



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  • David R Allen
    Was this an explanation for the origins of the ‘dominant side’ as in handedness? I vaguely recall the article, though not well enough to remember the degree of certainty expressed.



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  • . I have to work hard to remember my log ID for this forum. Sounds familiar though.

    I’m so pleased that I have ‘Remember Me’ on my device! I’d be hard pressed to come up with my password! 😉



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  • Handedness is not just confined to primates. Anyone that has ever done ring work with horses will tell you quickly that a horse will do better in one direction over the other. In the “on” direction the horse will be more cooperative, more flexible, even more comfortable to ride. In the “off” direction the horse is less balanced, less coordinated, less flexible, and some will even become defiant.
    Although I do own dogs, I have never attempted to train a dog in a discipline where speed, flexibility or balance are required (i.e. agility or balancing acts). But I am willing to bet that dog trainers would tell you the same thing.



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  • “That said, I know a couple of brilliant graphic designers who are left handed…”

    Dear CumbriaSmithy,

    Funny you should explicitly say that; surely you are aware of the fact that most artists throughout history were left-handed?



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  • Dear Eamonn,

    This is proper dinner table etiquette. It was developed centuries ago at the French royal court and, fortunately, throughout Europe and other civilized parts of the world (excluding America) it is still normal practice, and the only right way to eat (if you don’t want to make a fool of yourself).



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