LEFTHANDED UNIVERSE

ART

Picasso's Lefthanded Picador

Contrary to what is frequently claimed, Pablo Picasso in all probability was not a lefthander. Every single one of the hundreds of photographs of him that I have perused, shows him as a perfectly ordinary righthander: painting, sculpting, pointing, eating, drinking, smoking, everything is being done in ways that are normal for righthanders.

The history of the Lefthanded Picador too militates against Picasso's purported lefthandedness. In 1899, at eightteen, Picasso tried etching for the first time. It was to be a standing portrait of a picador, one who in a bullfight attacks the bull on horseback with a long lance. The result was a failure in every respect, but primarily because the picador unexpectedly turned out to hold his lance in his left hand: the inexperienced artist had failed to take into account the fact that in etching, every print is the mirror image of the original. He cleverly made the best of it, by putting El Zurdo, the Lefthander, over the picture. Honour was saved, but it would be five years before Picasso turned to etching again. Such a violent reaction is hardly to be expected from a lefthander!
More in The Lefthanded Picador, in the Books-section of The Lefthanded Universe.

Gabrielle d'Estrées Bathing with one of her Sisters

Gabrielle d'Estrées, on the right of the painting, lived at the French court during the second half of the 16th century. The woman on the left is presumed to be one of her sisters. She makes the crucial gesture of the painting, curiously, with her left hand. But Gabrielle too is acting lefthandedly, showing us a ring with her left hand.
Some experts attribute such unusual lefthandedness in paintings to compositional problems: once the painting was started, everything had to follow as it did. But that cannot be but a serious underestimation of the artist's professional skills. Moreover, it cannot explain why the seamstress in the background is performing her tasks lefthanded too.And with that, this painting is unique: it is the only one that is completely lefthanded.
Even more bizarre is what goes on behind the seamstress. The painting on the mantelpiece shows the lower part of a naked body. But look a bit closer. Isn't that a left arm, running partly across the torso and disappearing under the strategically positioned loincloth? Is this person masturbating? Masturbating lefthandedly?

Michelangelo's Lefthanded Adam

On the world famous ceiling of the Sixtine chapel in Rome, Michelangelo depicted, among much more, how God bestows life upon Adam. He does so with his right hand, of course. Adam, however, created in God's own image, receives this precious gift with his left. That is remarkable, for in christian religious art, lefthandedness is usually the sign of the devil. The idea that Michelangelo painted the scene this way merely because of compositional difficulties is hardly acceptable. A Pope who hires the best and most famous painter of his time to decorate such a holy place would not take kindly to such feeble excuses from his brilliant employee. Indeed, there is a very good reason for Adam's lefthandedness, one that was both recognizable and acceptable to the Church: the left hand is the part of the body that is symbolically most closely connected to the mysteries of sickness and health, of life and death.
This connection goes way back to the earliest times. It is not only apparent in the antique Isis-cult, but also, for instance, in the Roman Catholic custom of wearing the wedding ring on the left hand. This custom goes back on the Romans, who called the third finger of the left hand the digitis medicinalis, the health-finger. Also, the Roman writer Isidorus tells us how the Romans believed there was a bloodvessel running straight from this finger to the heart – so what better place was there for God to infuse life into Adam? More about these matters can be found in my book The Lefthanded Picador (see book-section)





The Lefthanded Artist's Signature

One way you can often spot an artist's lefthandedness is in his shading, especially in more casual sketches. Righthanders draw shading lines easiest from top-right to bottom-left. Lefthanders, of course, are more comfortable with the opposite direction, as this sketch of a skull by Leonardo da Vinci neatly shows.
It should be noted, however, that the direction of lines in shading is far from irrefutable evidence for anyone's right- or lefthandedness. When subtle effects are at stake, the paper is easily turned.

CURIOSITIES

The Left hand-Left leg Legend

The mere fact that there are only about 10% lefthanders, but around 30% leftfooted people shows that there is no direct relationship between the two conditions. The often heard claim (especially in pedagogical circles!) that differences between handedness and footedness indicate increased risks of impairments and learning difficulties is totally without grounds, and therefore dangerous

American Presidential Elections

Among the presidents of the United States of America there have been an unusually high humber of lefthanders - about one in every three. But in the 1992 elections, there was not even a righthanded candidate. Both the incumbent president Bush and his rivals Clinton and Ross Perot were lefthanders

Right-brained not rightminded

Regardless of popular mythology, there are no rightbrained people, as far as we know. The legend of the dominant hemisphere (cool, analytical, taciturn, left-dominant calculators versus warm, creative and artistic right-dominants) goes back to the sixties, when for the first time some discoveries about were made regarding the functions of the right half of the brain. But there is no proof whatsoever for dominance of either hemisphere, or even for a strict segregation of their operations. It is true that each hemisphere exclusively performs certain types of subprocesses, but most of what we do or think is the result of intensive and highly integrated cooperative efforts of both hemispheres. There are a few functions that we know to be intimately linked to certain specific regions of the brain. For instance, generally the left hemisphere contains a couple of areas that are essential for processing human language. This is also true for the great majority of lefthanders. Only a minority of lefthanders seems to have their langage areas wholly or partly in the right hemisphere - as do some righthanders. A different preferred hand does therefore not immediately imply a differently organised brain

Sire, there are no lefthanded Japanese

There are no lefthanders in Japan - at least not according to the Japanese. Recently, even the well known Japanese Internet pundit Yoichi Ito when I asked him flatly denied being lefthanded - oh, yes, he threw and drew with his left, but no, he was not a lefthander.
There was a time in Japan when mere lefthandedness in a wife was sufficient ground for expelling her. Today, things can't be as bad as that anymore, but even so lefthandedness is still severely repressed in schools and elsewhere. So vehemently, in fact, that serious Japanese researchers found less than two percent of the population avowing to being lefthanded, whereas everywhere else in the world this percentage hovers around ten. They attributed their findings to the exceptional characteristics of Japanese script, which they claimed could only be mastered with the right hand. That is nonsense, lefthandedness has little to do with writing, as many lefthanders who write with their right can testify. Rather, it is the implacably hostile attitude of Japanese society that is to blame for the sad fact that most lefthanded Japanese know better than to openly confess to their lefthandedness

Dyslexia lures the lefthanded?

Among almost any group of dyslectics there will be a slightly increades incidence of lefthandedness. But whether an average group of ordinary lefthanders would show an increased incidence of dyslexia is unknown. There is no research to that effect. The (small) increase of the percentage of leftahnders among dyslectics can be explained by the existence of traumatic handedness. If at birth, or shortly before, the brain becomes damaged in such a way that, among other things, the control over the preferred hand is impaired to such an extent that the weaker hand actually functions better, then the person in question will, to all intents and purposes, seem to be diffrently handed than he really is. Such children obviously often suffer also from other handicaps. Random brain leasions only seldom affect precisely one function alone. Since there are nine times as many naturla righthanders as there are lefthanders, the chance of an embryo becoming lefthanded by trauma is nine times as high as the opposite chance. The very rare traumatic righthanded then disappears into an ocean of natural righthanders, never to be spotted for what he really is, whereas the nine time larger group of traumatic lefthanders joins the 10% minority of lefthanders. As a result, they are conspicuously (but still only just measurably) present in every study of a group of sufferers from a variety of impairments induced by braindamage, such as (probably) dyslexia. Without dependable research among unselected groups of lefthanders, however, no conclusions can be drawn regarding connections between lefthandedness and such handicaps in general

Devilish Doors

It is a remarkably persistant misunderstanding that doors in general open the wrong way for lefthanders. There are four types of doors: door that one does not walk through (cupboards, refrigerators, washing machines), revolving doors, ordinary doors and car doors. Refrigerator doors usually have a grip on the left, so that they are best opened with the right hand. This seems to favour righthanders, but in reality it does nothing of the kind. For the lefthander immediately has his best hand free for performing whatever needs to be done inside the cupboard or refrigerastor, whereas the righthanded is obliged to use his weak hand, or to move his body completely to the left of the open door first. Revolving doors usually turn counter-clockwise, so that they must be pushed with the right hand. Such doors therefore indeed discriminate against lefthanders, but possibly this is due not to handedness, but to the rule that we keep right in traffic. Could people from England, Japan, and other left-driving countries perhaps shed light on this matter? Ordinary doors are mostly symmetric. If you encounter a door with the grip on the right and go through it, the grip will be on the left when you return. Doors preferably hinge on the side of the preferred hand when they are pulled open. One must pull the door open 'across the body', or one ends up behind the opened door instead of in front of an open doorway. If a door is pushed open, the same arrangement is best, albeit that the effect of pushing a door open with the wrong hand are less drastic. It's just cumbersome. Some say that the great majority of doors hinges on the right on the side where they are pulled open, thus favouring righthanders. My own countings, small as they are, fail to corroborate this claim in any way. Rather, it looks as if the ways doors are hinged is dictated not by handedness, but by other, mainly architectural factors, such as mirror-image building and the location of the door with respect to surrounding walls. Only French windows seem generally to obey a convention that, from the inside, the independently opening door is the right one, an arrangement which does favour righthanders. Cardoors have been favouring the lefthanded driver in all countires that keep right, ever since they all open front to back. The left hand doors can be opened solely by the left hand, both from outside and from within. sliding doors generally occur in the right side of cars in countries that keep right, and they too are best operated with the left hand. In left-driving countires, the opposite is the case. There, righthanded drivers have an edge on lefthanders

Unruly Scots

Scotland harbours many mysteries, including a clan that is believed to have had an unusually high proportion of lefthanders: the clan Kerr. This belief is so deeply engrained in Scotland, that corry-fisted and Kerr-handed have become common Scottish synonyms for lefthanded.
There is some evidence that the Kerrs may indeed have been unusual where handedness is concerned: the peculiar way in which they built their castles. Like most other castles, they have spiral staircases leading up the towers to the parapets. But the Kerrs built stairwells that wind counter-clockwise as you go up, quite contrary to custom, which prescribes clockwise-winding stairwells. The reason for the general preference for building stairwells that go with the clock is this. In case of an enemy breaking into the fortification, the attackers will try to fight their way up the stairs, with the defenders holding the top. On a staircase winding upwards with the clock, the defenders will have the central column on their left, leaving maximum space for their right hand to wield the sword or axe. The unfortunate attacker, however, has the central column to his right, blocking his movements.
The Kerrs built their stairwells the other way around for reasons that were buried long ago with the builders. One hypothesis is that the clan was predominantly lefthanded, so that they needed free space to their left. However, the advantage of having the stiars spiral the other way is only limited. For, while the lefthanded defenders gained room to move to their left, such stairwells also become more accomodating to righthanded attackers.
The Kerr clan still exists, its members having spread across the world during the times of the great emigrations of the 19th century. You can find them in America or Australia as well as in Scotland. It's home territory is in the south of Scotland, near Selkirk. The clan has two main branches, the predominantly catholic Feniehurst-branch, and the Cessford-branch, mainly protestants. The Cessford Kerrs own the largest stately home in Scotland, Floors Castle. Floors is featured in the film Greystoke, as the place where Tarzan is taken after leaving the jungle

ADDRESSES

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WRITING

There is no need for smudging, left-leaning letters or writing with a cramped 'hookhand', if you but know the trick. Three things are important:

•Righthanders should tilt their writing paper slightly to the left, so that the line from the tip of the pen to the elbow is at right angles with the line of writing on paper.
Lefthanders do the same, vice-versa: they should tilt their sheet to the right, so that for them too the line from pentip to elbow is at right angles with the direction of writing.

•Righthanders use a sweeping movement for writing, which originates predominantly in the pulse. It is not unlike peeling potatoes, really. Pulling movements yield heavy, downsloping lines, a push outside gives a thin, rising line.
Lefthanders employ a much different, subtler movement, more like pulling a splinter with a pair of tweezers. Heavy, falling lines result from a pullling movement caused by bending the fingers that hold the pen. The gentle push from stretching those fingers again gives rise to thin, rising lines.

•The subtlety of the lefthander's movements demand wellmade tools. Use a pencil, a fountain pen or a roller ball, but leave the clumsy biro to righthanders.

With the above method, the writing hand of a lefthander moves parallel to and underneath the writing line, just like the writing hand of a righthander does. Therefore, he does not lose sight of what is written, and the lefthander won't smudge his writing.


BOOK

Best non-fiction book on lefthandedness
My own, of course.
Nothing Left Unsaid: facts and fallacies of left and right handedness by Rik Smits
English edition in preparation. Click the title above to see more

The book discusses the deep influence of left/right dichotomies on culture, folklore and art and its interpretation, as well as the possible causes of (left-)handedness both in the individual and in the species, and its purported consequences.

Best literary work with lefthandedness as (a major) theme Levsja - the tale of the cross-eyed lefthander and the steel flea by Nikolaj Leskov first published in monthly magazine Russia, 1881

In this Russian tale of the tragic fate of a lefthanded gunsmith from Tula, Leskov plays neatly with almost every common association with lefthandedness in existence.

Other interesting fiction and non-fiction
The Left Hand of Darkness by Ursula K. Le Guin ACE books, 1969

Science fiction. A highly interesting book in that it deals with a world in which the usual dichotomies we live by, such as the gender dichotomy, don't apply. Le Guin rightly won both the Hugo and Nebula Awards for it.

L'ile des gauchers by Alexandre Jardin Gallimard, 1995 — ISBN 2-07-074030-7

A story about an Island inhabited by a lefthanded people, whose word for Lefthander derives from their word for Love.

The Ambidextrous Universe: Mirror Asymmetry and time-reversed worlds by Martin Gardner Basic Books,1964

Just what the title says: a book about forms of (a)symmetry in physical and biological nature.

Éloge du gaucher dans un monde de manchot by Paul Dubois Robert Laffont, 1986
— ISBN 90-6834-021-2

something like 'an ode to the lefthander in a one-armed world'. Comical, trivia.

CELEBRITIES

Famous Lefthanders

Artists
Media
Politics
Music
Academia
Sports
Writers
Underworld
Myths





TEST

How are you handed? Test yourself

http://www.xs4all.nl/~riksmits/


Contrary to popular wisdom, one cannot simply divide the world into two homogeneous groups: righthanders and lefthanders. Rather, there is a continuum, at whose extremes we find relatively small groups of very strongly left- and righthanded people, respectively. Most of us are somewhere in between, the great majority having a weaker or stronger predilection for the right hand. In broad strokes, the distribution is shown on the right.
For this reason, classifying people as left- or righthanders is not all that simple. There are many who will perform some tasks with their right, and others with their left hand. Moreover, certain activities, such as writing or eating, are unreliable indices, due to the social pressure that is usually exerted during the learning process. For example, even in left-tolerant societies like the United States or Holland, you won't find anyone who'll shake hands with his left.

The myth of the dying lefthanders

In 1991, psychologists Stanley Coren and Diane Halpern claimed they had found the average life expectancy of lefthanders to be no less than nine years shorter than that of righthanders. This dismal state of affairs was due to the clumsiness of lefthanders, combined with the fact that most machines and appliances are designed for righthanded use. As a consequence, lefthanders were simply accident-prone, resulting in an early death.
Fortunately, their claim is groundless. It is based upon a survey of almost 1.000 deaths in a county somewhere in Southern-California. At least nine months after a person had died, Coren and Halpern asked surviving relatives what hand the deceased used when writing, drawing and throwing a ball. People are notoriously unreliable in their answers to such questions even about themselves, let alone about their parent, uncle or niece, especially if the person in question has been dead for at least almost a year. Ask yourself about how many of your relatives you could confidently and correctly answer these three questions, and you begin to see how rickety Coren and Halpern's method for collecting data was.
But not only was their database unreliable, their analysis of the data is wrong as well. For one thing, they claim that lefthanders cause more lethal car-crashes, on account of an ill-conceived theory about 'reversed' reflexes: in a fix, a righthander would jerk the wheel to the right, out of the way of oncoming traffic, whereas a lefthander would do the reverse, going straight for the jackpot on the wrong side of the road. At first glance, this seems to tally with the fact that they did find a relatively high proportion of lefthanders dying in cars among their 1.000 deaths. Only, in view of the totla size of their sample, the actual number of lefthanded car crash victims was certainly no more than three. Far too little to draw general conclusions. Also, it seems that they just counted deaths in cars, disregarding the questions whether the car with the lefthander in it was to blame for the accident, whether the accident was a head-on collision with another car (the only type of accident that would be relevant in the light of their 'reverse reflex' theory) or whether the lefthander involved was even driving the car at the relevant time.
Also, Coren and Halpers claim that the proportion of lefthanders among the population at large decreases from 20% at the age of 20 to a mere 5% among fifty-year-olds. That means that, even if all deaths between those ages should be lefthanders, the death-rate in this age-range should be around 15%, whereas in reality it hovers around 5%. Coren and Halpern have large numbers of people die who never existed.

Righthanded Toads

In early 1996 a team of Italian and Australian researchers reported having found for the first time a (front)paw preference in amphibians: the European Toad (bufo bufo). Unitl then, paw-preference had only been found in certain species of mammals and birds. The researchers made their discovery by sticking a wet piece of paper onto the nose and mouth of toads, or drawing a small ballon over their heads, and watching which paw they used first in trying to rid themselves of the obnoxious thing.
Almost six out of ten toads turned out to be right-pawed, with only one in six preferring the left paw. The rest showed no clear preference. This is a remarkable finding, since chance would predict a quarter of the population to be right-pawed, another quarter left-pawed, and the rest neutral, if there is pawedness at all. So there must be some special reason for the this deviant distribution of pawedness.
It is, of course, tempting to assume a connection with human hand-preference, which is biased towards the right even stronger. In that case, lateralization, the phenomenon of the brain-halves developing differently, each wth its own specializations, would than go back at least as long as the common ancestor of man and toad.
That, however, is probably a bridge too far. Tomio Naitoh of Shimani University in Japan and Richard Wasserung of Dalhousie University, Halifax, Canada, reported shortly after that toad are used to getting rid of toxic and indigestable food remnants through the mouth. They do so by 'spitting out' their entire stomach, and wiping the stomach lining with a paw. Since toads' stomachs are asymmetric, they always hang out on the right side of the mouth, so toads forcibly use the right paw for cleaning it.
Possibly, then, the observed preference for the right paw can be explained by some toads responding to the 'thing' on their heads as if they had turned out their stomach. In that case, paw-preference exists, but is a result of the visceral architecture of the toad, not necessarily lateralisation of its brains. The similarity to human handedness may therefore be coincidental.
Sources:
A. Bisazza e.a., Right-pawedness in toads, Nature 379, 1 February 1996
T. Naitoh & R. Wasserung, Why are toads right-handed?, Nature 380, 7 March 1996

Medieval Lefthanders?

Across the world, the proportion of lefthanders today is roughly ten percent. But howmany were there in earlier times? There are no surveys to go on. Researchers of the University of Southhampton and the English Heritage's Ancient Monuments Laboratory claim they have found evidence that in medieval times the proportion of lefthanders was slightly higher than today.
They measured the length of the arm bones of 80 peasants who had been buried in a cemetery in Wharram Percy, a village in Yorkshire, England, from the 11th to the 16th century. In 16% of the cases, they found the left arm to be somewhat longer than the right. Three percent had arms of equal length, in the rest, the right arm was the longer. Assuming that the dominant arm would be used more for carrying things, and would therefore develop more strongly than the other, they concluded that the proportion of lefthanders was slightly higher in those days. They attributed this difference to the lack of cultural pressures favouring the right hand in the illiterate society these peasants lived in.
It seems an attractive line of reasoning, but whether it really holds water remains to be seen. First, it is not at all clear that the dominant arm actually does develop more strongly in general. Second, one should be aware that, even in the most left-repressive societies, the tasks that are typically subject to pressure favouring the right hand are skills that require little or no strength: writing and eating.
Further details at: Medieval Lefthandedness
Source: G. Ferry, Yorkshire churchyard tells a sinister story, New Scientist 26 August 1995

Are lefthanders crypto-twins?

In 1967, psychologist Subirana lamented that lefthanders seemed to exists solely to make the life of neurologists miserable. However, judging from what went before, one might as well claim that twins were invented to thwart explanations of lefthandedness. Whichever way we look at it, twins are always and conspicuously in the way.
Might there not be a lesson in this, an indication that all attempts at explanation that we have considered so far, tackle the problem from the wrong angle? Twins are a special group. So special in fact, that we are used to class them as exceptions without further ado. But what if that were not correct in the case of lefthandedness? What if twins, however rare they may be, constitute the normal case. What if, in reality, the lefthanded singleton were the exception? Of course, it's a tricky and slippery thing to propose, but as a thought experiment it certainly has appeal. So let us see where such a line of reasoning would take us. For the moment, we will consider only monozygotic twins. However improbable our starting point may seem, there are at least three facts to cling to. Fact one: lefthandedness is roughly twice as common among twins as among singletons. This is a well established fact, which becomes interesting when we combine it with fact number two: lefthanders turn out to be roughly twice as likely to produce twins as their righthanded brethren. This entails that not only is there a connection between twinhood and lefthandedness, but also between twin-parenthood and lefthandedness.
The third fact is that lefthanders are roughly twice as likely to have a lefthanded child as righthanders. Taking the liberty to combine this third fact with the other two, we see that lefthanders show equally increased chances of having twins and of having lefthanded offspring. This looks like a promising state of affairs.
The next step tyo take is a bold one. Let's suppose that monozygotic twinhood is at the root of lefthandedness. That only embryos that split may yield one or two lefthanded individuals. The beauty of this supposition lies in the fact that it requires just a single hereditary property to explain both lefthandedness and the existence of twins. This property would be a stronger or weaker tendency to have one's embryos split during the early stages of pregnancy. If this single tendency would be relatively strong in lefthanded parents, all three the above facts might follow.
Attractive as this may seem, doesn't the fact that monozygotic twins are much rarer than lefthanders sink our theoretical ship even before it reaches open sea? For how could every lefthander be a twin, if for every birth of a pair of monozygotic twins, scores of lefthanded singletons are born? To see why this obvious discrepancy does not stand in the way of our line of reasoning, we have to look into the process of twinning itself a bit.
In monozygotic twinning, at some point during the first eight to nine days after conception, the clot of cells that is developing into a real embryo splits into two roughly equivalent parts, each of which will grow into a complete and independent embryo. That is, if all goes well. How often, or how rarely, all does indeed go well, is a matter of speculation. If one of the two parts is not viable and dies off, it is still so tiny that it will disappear unnoticed and without trace. In fact, we have but little insight of what really goes on when twins are formed. What we do know, is that the popular notion of a fertilized egg immediately splitting, in a way similar to ordinary cell-division, is incorrect. This notion has been established by the well-knowns experiments with eggs of salamanders, which are split by a hair, after which both parts go on to develop into a complete and separate individual. Not so in the world of the human womb. Human twins usually originate much later in the process of development. Four days after conception, a membrane forms around the cell-clot into which the fertilized egg-cell has by then developed. This membrane, the so-called amnion, contains both members of a pair of monozygotic twins in one of every three cases. This tells us that in one third of all cases splitting occurred after the amnion was formed. Around day seven, a second membrane develops, the chorion, which is shared by almost all pairs of twins. A sizable proportion of monozygotic twin pairs therefore arises between the fourth and seventh day of pregnancy. The rare cases of twinning after the seventh day usually yield unpleasant results, among which all cases of Siamese twins.
The importance of the fact that twinning can be, and often is, a relatively late process, is that twin formation is a process of considerable complexity and therefore risky. If only a single cell was involved, little could go wrong. Division is a process which cells in general have mastered to perfection. Splitting a structure consisting of a fair number of cells in such a way that both parts comply with all the requirements for further development, however, is an altogether different matter. How mother nature nevertheless regularly succeeds in doing so, is an open question.
Let us tentatively answer that question in the simplest possible way, by supposing that there is no specific procedure at all: if an embryo splits, it does so at random. It is a simple, but also inefficient method. In the large majority of cases, one of the resulting parts will contain insuffient material for further development. At the same time, these minimal assumptions put us in precisely the right position: all those unhappy splits will ultimately yield only one individual, as if nothing had ever happened. In other words: most of the children who started out as twins in early pregnancy, are eventually born as singletons. Remember, however, that this entails that the number of divisions of embryos is a multiple of the number of successful divisions, and thereby of the incidence of twin-births. If what we propose is right, the successrate should be in the range of 0.5 to 1 percent.
Now let us return once more to our starting point: lefthandedness arises from embryonic splitting. A corroborating indication that this might indeed be so is the fact that splitting occurs in the same developmental phase during which the very first foundations of symmetry are laid, and perhaps also of the assymmetries within the overall symmetry. In a number of cases, one can observe a reversal of such assymmetries in monozygotic twins. A well-known example of this is the shape of bodyparts like the ear, which will have the exact same shape on the right side in one twin as it has on the left in the other. Along similar lines, we might suppose that we are all destined to righthandedness in principle, but that splitting may in some cases reverse this asymmetry, causing one of the twins, and occasionally even both, to become lefthanded. Mind that this is no more than a limited disruption of the ordinary asymmetric development, and does not necessitate a complete reversal. Lefthandedness may thereofre occur in many gradations, and accompanied by zero or more other deviations from the normal distribution of, for instance, functions among the halves of the brain.
If any of the above is true, the chance of any individual deriving from a split embryo being lefthanded should be around 20%. This is the proportion of lefthanders among monozygotic twins, resulting from split embryos both parts of which were viable. The large number of unsuccessful splits causes the number of lefthanders among the population at large to be roughly 10% only.
Might it really be so? That must remain an open question. Better founded explanations for all sorts of phenomena have proven to be false. What we di here, was no more than a speculative thought experiment. At any rate, we did Subirana a good turn, for we relieved the neurologist community of their unpleasant task, delegating is to the embryologists, who must find out the details of twinning.
But even then there is still no end of it. Twinning may explain how lefthandedness arises, and why it occurs in the proportions we observe. But what (left)handedness essentially is, the details of how it works, remains a mystery even then.

Sources: Rik Smits De linkshandige Picador/ Alles mit der Linken Hand, Nijgh & van Ditmar 1993 / Rowohlt 1994.


bace punye bace...aku tangan kanan rupenyer heheheh