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The Evolutionary Mystery of Left-Handedness (2014)


“Sahara is too miniature tag / to pay for thy Factual hand,” Emily Dickinson wrote in a poem. “The accurate hand = the hand that’s aggressive, the hand that masturbates,” Susan Sontag pondered in her diary in 1964. “In consequence of this reality, to rob the left hand! … To romanticize it, to sentimentalize it!” The human hand has long carried cultural baggage, and but we quiet fight to unclutch from it the myths and show the realities.

The ask of why some humans are left-handed — along with such vital specimens as Plato, Charles Darwin, Carl Sagan, Debbie Millman, Stephen Jay Gould, Noam Chomsky, and Albert Einstein— has at a loss for phrases scientists for centuries. For Southpaws themselves — the affectionate term for lefties — this natural peculiarity has been everything from a provide of stigma to a diploma of pride. But on the heart of it stays an evolutionary mystery — one that Wired contributing editor David Wolman, himself (however obviously) a lefty, sets out to investigate in A Left-Hand Flip Across the World: Chasing the Mystery and Which methodology of All Issues Southpaw (public library).

Wolman, who spoke regarding the oddity of handedness in an unprecedented contemporary Radiolab episode about war, traces 200 years of natural and psychological perplexity as he scours the arena for answers, from a Parisian science museum that houses pioneering French surgeon and pupil Paul Broca’s bottled brains to a castle in Scotland that hides clues to the heritability of left-handedness to the neuroscience labs of Berkeley to the golf programs of Japan.

To be particular, a Southpaw wasn’t constantly a mere scientific curiosity, now not to mention the “lefty superiority complex” which Wolman both notes and embodies — for centuries, it became the topic of superstition, which bestowed upon its proprietor a severe social curse. Wolman writes:

In the Western world, left-handedness has long been associated to the worst of the worst: sin, satan admire, Satan himself, and accurate an all-spherical detestable space with God. Catholic schoolteachers historical to narrate students that left-handedness became “the tag of the Beast,” the Scots jabber an individual with unpleasant success will ought to were baptized by a left-handed priest, and orthodox Jews wrap their left fingers in the leather-basically based fully mostly strap of tefillin as if to jabber, in the phrases of Rabbi Lawrence Kushner: “Here I’m, standing with my unsafe side bridled, ready to hope ” The Bible is stout of references to fingers, and usually they are about God doing something benevolent and holy along with his accurate hand. I’ll spare you the bustle-through and stick to a token instance, admire this one from Psalms 118: “The accurate hand of the Lord is exalted. The accurate hand of the Lord doeth valiantly.”

Carl Sagan, a lefty

Whereas Carl Sagan once hypothesized that the cultural hyperlink between left-handedness and badness arose attributable to the left hand’s exercise for hygiene functions in nonindustrialized international locations, Wolman aspects out that the association has mighty deeper roots, along with the very etymology of the word “left”:

The Anglo-Saxon lyft methodology outdated or broken, and even popular dictionaries include such meanings for left as “unsafe,” “crippled,” “awkward,” “clumsy,” “inept,” and “maladroit,” the latter one borrowed from French, translated literally as “detestable accurate.” Most definitions of left lower to an image of doubtful sincerity and clumsiness, and the Latin word for left, substandard, is a renowned elegance. From this version springs my favorite term for left-handedness, “the bend substandard,” which Vladimir Nabokov historical for the title of a e book that has nothing to attain with handedness.

Even as of late, our idea of handedness is muddled by misconceptions. Whereas it’s on the 2nd estimated that 10-12% of the human inhabitants is left-handed, the very definition of handedness is decided off for confusion:

Most folks presume the hand historical for writing is the litmus test for determining whether any person is lefty or righty, and for any individual snarl material to dwell with a pedestrian stage of files on the topic, this slim reading will serve neatly ample. [And yet] day to day tasks, admire throwing and engaging, additionally impact the popular idea of hand dominance, in most cases nearly as strongly as writing. These assorted behaviors lead on to a quintessential area of handedness inquiries: be taught the intention to define handedness itself. The definition of lefty or righty varies, in most cases to a frustrating stage, and that variation has timid researchers who want to catch a bigger handle on why it is that humans private hand need and efficiency discrepancies in the first space, where these discrepancies reach from, and why as a inhabitants we veritably need the accurate hand.

Also to be accounted for is the proven reality that many of us are born with a natural inclination to jot down with the left hand however are schooled out of it for diversified causes. (I in point of fact, an adult righty, am amongst them. The most visceral proof is came all the map in which through on my left thumb, whose pad an elongated scar splits vertically. It became inflicted while carving a watermelon jack-o-lantern at age six and unintentionally flipping the knife the substandard map, pressing onto its edge in want to its blunt side. The truth that I held the knife in my left hand is cited to this existing day as indication of my natural left-handedness. The truth that I held the knife at all is cited as indication of questionable parenting.)

The most steadily historical test for handedness is that this spoiled stock created in the early 1970s, which generates what researchers name a laterality quotient:

Aloof, even though we had been in a location to codify handedness, the ask of why the dichotomy exists in the first space stays launch. But sooner than diving into the diversified theories, Wolman offers an a really worthy primer on how the mind works:

It’s a renowned side of the mind-body relationship that rob a watch on of circulate is crisscrossed. That is, the act of swatting at a buzzing mosquito with the accurate hand is controlled by the left side of the mind, or more particularly by a selected space of the left hemisphere is known as the left motor cortex, which sends the a really worthy indicators to muscle groups in the accurate arm. The reverse is correct for actions performed with the left hand, and all of here’s irrespective of handedness. The hemisphere on the same side as a circulate isn’t fully tranquil … however for the most phase motor rob a watch on comes from the reverse hemisphere. This contralateral rob a watch on, first described by Hippocrates himself, isn’t minute to fingers. It applies to fingers, legs, eyes, ears, and certainly impartial about all motor colleges, which is why americans that’ve had a stroke or tumor on one side of the mind veritably skills partial or entire paralysis on the reverse side of the body.


The left and accurate sides of the mind are physically pretty clear. The mind is made up of two mostly separate halves, every quiet of billions and billions of neural connections. But irrespective of popular notions to the contrary, left-handed americans attain now not mediate in the accurate hemisphere of the mind, nor attain accurate-handers mediate in the left hemisphere. The motor cortex, that phase of every hemisphere defective-wired to manage the opposite side of the body, is only one moderately minor side of this dizzyingly complex organ, and it says nothing or nearly nothing about an individual’s thoughts or personality.

So what can the mind show about handedness? One in every of the first scientists to ponder the mystery of left-handedness became pioneering French surgeon Paul Broca, whom Wolman calls “the closest aspect the religion of Southpaw has to a prophet.” In 1861, accurate two years after Darwin had came all the map in which through the rules of evolution, Broca encountered two patients who stumped him profoundly. One became an epileptic man named Leborgne however is known as “Tan,” nicknamed after the one syllable he became able to uttering. Leborgne became in a location to love spoken language however couldn’t inform his thoughts in speech — something that at a loss for phrases Broca very a lot, doubly so offered that one of Leborgne’s first signs became a weakening of feature in the accurate side of his body, which progressed to more loss of motor rob a watch on and at closing the loss of spy and just a few of his mental colleges.

When Leborgne died on the age of 51, Broca made up our minds to crack the mystery — literally. He dissected Leborgne’s mind and came all the map in which through a large lesion in the left frontal cortex, doubtless attributable to a tumor. Broca concluded that this ought to somehow be associated to Leborgne’s signs, of which the loss of speech became the most dramatic. But an instantaneous hyperlink would purchase longer to recuperate.

Then got here Lelong, an aged patient who had ended up in Broca’s care after a tumble, only in a location to say just a few phrases. When Lelong died two weeks later, Broca came all the map in which through a equally dramatic lesion in the left side of his mind, which is preserved to this existing day in Paris.

But the most perplexing of Broca’s patients had been the few who had either had damage to the left hemisphere however no difficulties with speech or who had misplaced their potential to talk however only had damage in the accurate hemisphere. This led Broca to place that for a minority of americans, the speech centers had been positioned in the accurate in want to left hemispheres, which he before everything idea would be tied to handedness, however later surmised that both phenomena had been anomalous exceptions and weren’t correlated. Aloof, his work became the first principal spark for the survey of handedness and stirred pretty the flurry interior the scientific community. Wolman aspects out the conflict between science and popular tradition that ensued:

Because some persons are an exception to the language-to-the-left rule, and attributable to a equally runt percentage of persons are left-handed, each person and his cousin in the scientific establishment figured the 2 ought to jog hand in hand; lefties ought to private language lateralized to the accurate. What’s attention-grabbing about this conclusion is that few americans in nineteenth-century Europe would private admitted to being left-handed. Detecting any person’s left-handedness would were sophisticated, with engaging, writing, and other fundamental tasks all veritably performed with the accurate hand. What’s additionally attention-grabbing about this conclusion is that it’s substandard. Virtually 99 p.c of accurate-handers private language positioned in the left hemisphere, and about 70 p.c of lefties attain. A special percentage, superb, however veritably the reverse; most lefty brains are admire righty brains, a minimum of as some distance as speech feature is alive to. The remaining either private language in the accurate hemisphere, or private it disbursed more evenly between the 2 sides of the mind.

Paul Broca

Despite the proven reality that Broca himself had gently brushed aside the hyperlink between handedness and accurate-hemispheric speech dominance, he hadn’t gone out of his intention to express the dissociation, so the delusion that lefties had their speech positioned in the accurate hemisphere persisted for nearly half a century. It wasn’t till WWI, when physicians began to spy that injured veterans who had been lefties didn’t necessarily private accurate-hemispheric language localization, that the delusion began to erode and the hunt for heed spanking contemporary theories won momentum.

Wolman aspects to just a few of the vital theories that adopted, every in flip disproven by science however offering a treasured portion of the quiet-unfinished puzzle. One in every of the earliest proposed that handedness in humans became before everything evenly disbursed, however hand-to-hand battle in the historical world killed off the lefties attributable to they held the sword with their left hand and the defend in their accurate, thus leaving the heart mighty less derive than for righties, who held the defend on the left. As the lefties perished on the battlefield, so did their genes.

The idea became disproven for a series of causes, along with the proven reality that there is proof of left-handedness long sooner than the invention of the sword and defend as well to the natural reality that the heredity of handedness isn’t so easy.

A later thought proposed gorgeous mighty the reverse — that left-handedness gave warriors a competitive advantage “for mighty the same reason left-handed tennis avid gamers, boxers, or fencers private a bonus.” Wolman cites the instance of a left-handed 16th-century Scottish warrior from the popular Kerr clan:

The lefty advantage exists attributable to, in an world with some distance fewer lefties than righties, accurate-handed, and even left-handed, opponents private comparatively miniature practice going through off in opposition to left-handers. Lefty forehands are hit from that less familiar side, their stronger punches place from that less delighted side, and their opposing stance differs from what persons are accustomed to, namely accurate-handed opponents. For Andrew Kerr, the matter became of some distance better import than for, jabber, John McEnroe serving up one other ace to the advert-courtroom at Wimbledon; for Kerr, success with the sword became a matter of lifestyles and loss of life.


French scientists now not too long up to now hypothesized that fighting advantages for left-handers in prehistoric human societies ensured reproductive success. To envision the root, they regarded on the cancel rates in diversified societies, questioning if the Southpaw advantage would be magnified interior traditionally more violent populations. From the outcomes, it looks to be admire it became, with proportions of left-handedness ranging from 3.4 p.c in an especially pacifist African community in Burkina Faso to 22.6 p.c in a notoriously violent tradition in South The US. Southpaws aren’t more violent, obviously, however could doubtless additionally private had a survival advantage in societies that had been.

Aloof, these hypotheses had been never proven with any stage of verifiability. Speedily-forward to the leisurely 1970s and early 1980s, when Harvard neurologist Norman Geschwind proposed a thought that persisted for heaps of years: He instructed that prime phases of testosterone in the womb led to a minor mutation in the mind, which prompted its group to shift away from accurate-handedness. One strengthen level cited for his thought is the proven reality that there are a miniature little bit of more male lefties than female.

An earlier womb thought had posited that the fetus’s orientation interior fosters its sense of balance, so handedness is in response to whether the fetus uses the left or accurate hand for balance — the free hand, in most instances the accurate, can then transfer and explore, finally turning into the dominant one.

But but again, neither thought came all the map in which through ample strengthen. And so we return to the mind and genetics. Wolman cites the work of English researcher Marian Annett, who came all the map in which through the predominant to the messy heredity patterns of handedness:

In 1972, Annett … published a paper titled, “The Distribution of Manual Asymmetry,” which, even supposing of miniature spy on the time, would later operate the muse for one of many most veritably well-liked explanations of human handedness. She called it the Factual Shift Idea, and she or he later expanded it in a 1985 quantity of the same title. Annett argues that whereas human handedness is rather like the left- or accurate-side preferences exhibited by other creatures with fingers, paws, feet, or what private you ever, the approximate 90 p.c predominance of accurate-handedness in the human inhabitants sets us apart. All other animals private a 50-50 spoil up between righties and lefties. In accordance with Annett’s model, handedness in nature rests on a continuum, ranging from stable left, through blended, after which to stable accurate-handedness. But for humanity the distribution of need and efficiency is dramatically shifted to the accurate. Human bias to the accurate, Annett explains, became prompted by a shift to the left hemisphere of the mind for particular cognitive functions, in all likelihood speech. . . . That momentous shift became prompted by a gene.

Obviously, that ask had at a loss for phrases generations of scientists since Darwin — who, incidentally, became a victim of the confounding heredity of handedness: his principal other and principal other’s father had been lefties, however only two of Darwin and Emma’s ten formative years had been. But Annett’s Factual Shift Idea became the first systematic clarification for the genetics of handedness. Aloof, Wolman observes the complexities of genetics:

In some ways, the genes-versus-atmosphere dichotomy is a deceptive one attributable to so veritably the 2 work hand in hand. Jabber, as an illustration, a gene or genes instructs for a particular amount of testosterone in the womb. If the stage of that hormone varies and somehow influences the construction of the fetus, ought to traits tormented by the stage of testosterone be dubbed genetic or environmental? One could doubtless additionally argue that the biochemical instances in the womb-the fetus’s environment-qualify as environmental components, however those instances are formed by genetic directions. But interior the DNA of every cell of that newborn baby, there will doubtless be no files particular to the baby’s instances in the womb. Will we name that a genetic trait? Fortunately, Annett’s thought supposes a less ambivalent feature for a gene, or doubtless just a few genes. Contained in the nuclei of nearly every cell in the body are left-twisting bundles of DNA that either attain or attain now not comprise what Annett has dubbed the “Factual Shift aspect.”

What this series of hypotheses unearths, bigger than anything else, is correct how miniature we know regarding the interior workings of the body — irrespective of getting sequenced the human genome, here we’re quiet struggling to level to as apparently straightforward a characteristic as handedness. And but, Wolman argues, Annett’s be taught became groundbreaking and immensely treasured for three causes: “the root of a handedness continuum; the chance-basically based fully mostly gene predicting now not individual handedness however shifted inhabitants distribution; and at closing the advice that folk are now not left-handed or accurate-handed, however accurate-handed or non-accurate-handed.”

Fundamental art work from ‘A Visible History of Magic.’ Click on photos for principal aspects.

Most definitely the most attention-grabbing thought, nonetheless, is a sexy fringe proposition that ties handedness to “magical ideation” — one’s tendency to judge in metaphysical phenomena previous that aren’t scientifically verifiable, from supernatural forces to extrasensory perception to reincarnation and other ideas that wouldn’t defend up to Carl Sagan’s Baloney Detection Kit. Wolman cites Contemporary Zealand pupil Michael Corballis, who has written regarding the functionality hyperlink between more mind symmetry — something existing in lefties — and magical ideation:

Hemispheric asymmetry itself could doubtless additionally lead to more decisive and controlled action, and doubtless a bigger potential to prepare hierarchical processes, as in language, fabricate, and really appropriate thoughts. These americans who lack cerebral asymmetry [a.k.a. increased symmetry] would be more at chance of superstition and magical taking into consideration, however more creative and doubtless more spatially conscious.

On the magical ideation scale — the measure of belief in such phenomena — lefties are inclined to ranking better than righties. And but, Wolman aspects out, “anecdotal proof that lefties are extremely represented in low-bullshit-tolerating professions reminiscent of journalism and science doesn’t precisely strengthen this idea,” suggesting as a alternative that the magical ideation hypothesis is supreme “recalibrated as a stage-now not-route descriptor.”

What makes this thought keen, nonetheless, isn’t its verifiability or lack thereof however what it unearths about our tradition’s beliefs about creativity and mental illness, or cognitive abnormality. Wolman writes:

The magical ideation line of taking into consideration loops lend a hand to creativity after we rob in thoughts findings indicating an increased percentage of left-handers who’re tormented by such disorders as schizophrenia. With due acknowledgment all over but again to Corballis for synthesis of this idea, it’s plausible that schizophrenia and magical ideation sprout from identical neurological roots. Be taught demonstrating connections between blended-handedness and either of those two instances advances that plausibility.


Take into myth for a 2nd that there’s a thin, doubtless blurred line between genius and mental illness. What if some forms of genius stem from the same side of the mind — or impact on the mind — as, jabber, magical ideation and schizophrenia, and that refined variation in the draw of particular mind circuits determines the variation between the subsequent da Vinci, the subsequent graphology believer, the subsequent Hendrix-admire guitar god, or the subsequent schizophrenic?

Albert Einstein’s mind (Photo: NMHM, Silver Spring, MD by potential of Nature)

Wolman aspects to Kim Sight, the autistic “megasavant” on whom the movie Rain Man is basically based fully mostly, and doubtless most notably Albert Einstein, neatly-steadily called “the quintessential popular genius”:

Examination of his mind after loss of life showed habitual anatomical symmetry that … can suggest above-customary interhemispheric connections. Then there’s the proven reality that Einstein’s genius is frequently linked with an imagination supercharged with imagery, a extremely accurate hemisphere-dependent feature. It became that selection of imagination that ignited questions main finally to the Idea of Relativity: what does an individual on a transferring prepare glimpse when compared with what an individual standing quiet sees, and how would the body age if touring near the whisk of light in a spaceship when put next with the aging job noticed on Earth? Is it such a stretch to invest that Einstein landed on the fortunate stop of the same mind group spectrum upon which other, less lucky americans land in the mental illness category? And what if handedness too is influenced by this organizational crapshoot?

Illustration by Vladimir Radunsky for ‘On a Beam of Gentle: A Epic of Albert Einstein.’ Click on image for principal aspects.

The investigation is ever-ongoing, however Wolman offers a wealth of alternative discontinuance-giving findings and theories in the rest of A Left-Hand Flip Across the World.

Einstein’s handedness is a miniature little bit of a matter of debate. Whereas he is frequently cited amongst history’s popular lefties, laterality students private surmised that he became blended-handed — which is now not to be puzzled with ambidextrous: blended-handed americans exercise the accurate hand for some issues and the left for others, whereas the ambidextrous can exercise both fingers equally neatly for heaps of tasks.

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