James L. Franklin, MD
Paper presented to the Chicago Literary Club on April 7, 2008
It all began on the coldest morning of the season in early December 2006. Painters were still in our apartment putting the finishing touches on what had proven to be an all too prolonged renovation project. However—the end was now in sight, and I was dearly anticipating a return to normalcy. Rushing home with packages in both hands including hot soup purchased for a lunch I hoped to share with my wife, I tripped and fell crossing the street at the corner of Rush (ominously named) and Bellevue on Chicago’s near North Side. Careening forward, my outstretched grasp was directed by a simian reflex etched for eons on my nervous system toward an elusive tree limb that materialized in the form of a cold hard concrete pavement. Gathering my packages and quickly pulling myself up so as to hide the embarrassment of my fall, I was too cold to feel any pain. One glance at my deformed right hand told me I was in need of help. Proceeding home quickly, I was able to contact a friend, colleague, and outstanding Chicago hand surgeon, Robert Schenck. Bob saw me in his office that afternoon (thereby avoiding a dreaded trip to an emergency room), and an x-ray quickly confirmed that I had broken a bone, the middle phalanx of the fourth digit of my right hand. The fracture extended to the middle interphylangeal joint, an unfavorable finding, and plans were made to surgically pin the fracture. It was also necessary that my right hand, wrist, and forearm be largely immobilized for three months in a combination splint and traction device designed to treat this type of fracture so as to preserve the function of the affected joint. I would have to adapt to having the use of only one hand. For a devoted amateur pianist, it is an understatement to observe that this was a disheartening turn of events. As a physician blessed by the relative freedom from ill health, I wanted to be a “good patient” and resolved to make the most of the situation.
Learning to adapt to the use of one hand quickly informs one that much of our daily activity depends on a well-choreographed pas de deux of bimanual skills. Try typing your next Literary Club paper with one hand (do not despair; voice recognition systems are a work in progress). Being left-handed, I reflected on the advantage the dexterity (note the diction) my left hand afforded in adapting to this disability. Happily, I could use a fork with my left hand as I was accustomed to doing, and that essential modern survival skill, signing credit-card charge slips, was well preserved.
Lest I appear to imply that my case was unique, allow me to quote from a short article by Walt Whitman, “Left-hand writing by soldiers,” from April 30, 1866:
Here is a single significant fact, from which one may judge the character of the American soldiers in the just concluded war: A gentleman in New York City, a while since, took it into his head to collect specimens of writing from soldiers who had lost their right hands in battle and afterwards learned to use the left…I have been looking over this writing. A great many of the specimens are written in a beautiful manner. All are good. The writing in nearly all cases slants backwards instead of forward.
Not wishing to abandon the piano for a period of months, I remembered the existence of solo piano music written for the left hand. I was pleased to find in my home music library a prelude and nocturne by the Russian composer of the late 19th and early 20th century Alexander Scriabin, as well as an arrangement by Johannes Brahms of the famous Bach Chaconne for unaccompanied violin from his Partita in D Minor. A good friend called my attention to an Internet Web site devoted to left-handed solo piano music giving the details on over 450 composers who had written piano music for the left hand alone.
Why was such a volume of music written for the solo left hand at the piano and virtually none for the right hand alone? Noteworthy is the story of the pianist Paul Wittgenstein, scion of a cultured and wealthy fin-de-siècle Viennese family and brother of the philosopher Ludwig Wittgenstein. After tragically losing his right arm fighting in World War I, Paul Wittgenstein overcame his injury and achieved international fame as a left-handed piano soloist. He expanded the repertoire, utilizing his considerable financial resources to commission several prominent composers to write works for piano solo left hand and symphony orchestra. The composers he commissioned to write concerti included; Richard Strauss, Benjamin Britten, Sergei Prokofiev, and Paul Hindemith. Wittgenstein’s musical tastes were quite conservative, and he was less than pleased with the works of Prokofiev and Hindemith, which he never performed. The most famous composition to emerge from these commissions was Maurice Ravel’s concerto for piano left hand which remains in the repertoire to this day.
There are several other explanations for the prominent body of left-handed piano literature. Most pianists being right-handed, a pedagogical need was perceived to make the left hand equal in skill to that of the right hand. Speaking to this need, Leopold Godowsky, the famous Polish-American virtuoso of the early 20th century, included 22 arrangements for the left hand alone in his daunting “Paraphrases on Chopin’s Etudes.” Another explanation relates to the greater technical demands made on the right hand in the piano literature, leading to an increased likelihood of its being injured as a result of intensive practicing. This happened to Scriabin in 1898 when, as a student in the St. Petersburg Conservatory, he competed with two of his fellow students, Sergei Rachmaninoff and the legendary Josef Lhévinne, for the outstanding performance of Liszt’s devilishly difficult Don Juan Fantasy. The contemporary virtuoso Leon Fliescher made a career as a left-handed piano soloist after injuring his right hand through prolonged and repetitious practicing which caused a neurological syndrome occurring frequently in musicians known as dystonia. The explanation for the wealth of left-handed piano music I find most interesting relates to the left hand itself. The left hand is oriented relative to the piano such that the strong thumb, index, and third finger are positioned to project a melodic line above an accompaniment that is executed by a combination of the third, fourth, and fifth digits. This argument is supported by the virtual absence of solo piano music for the right hand.
In June 1877, Johannes Brahms sent Clara Schumann his arrangement of the Bach Chaconne. Fortuitously, Brahms sent the manuscript at a time when Clara’s right hand had been injured in a kitchen accident and was preventing her from playing the piano. In early July she responded, informing Brahms that she derived enormous pleasure from playing this difficult piece and comments that “my right hand itches to join in.” This was contrary to my own experience during the early months of 2007 while I explored the piano literature for the left hand alone. I felt that it was quite natural to project the expressive content of the music with my left hand. This observation provided the answer to a conundrum over which I had often puzzled. Why were the stringed instruments, both across cultural divides and throughout the ages, constructed so that the notes were played with the left hand and the strings bowed or plucked with the right hand? The rapid fingering of these instruments seemed empirically to demand the greatest dexterity, yet this was given to the left hand, while the bowing or plucking, not without its own set of challenges, was relegated to the more agile (at least for the majority of the population) right hand. Affirming this line of reasoning, Charlie Chaplin, a left-hander, tells us in his autobiography that he had the bridge and stringing of his violin altered so he could learn to play the instrument as a “lefty.” Chaplin plays the violin left-handed in two of his films, The Vagabond (1916) and Limelight (1952). I believe that answer to the question is that in the performance of a string instrument, the expressive content of the music is rendered by bowing or plucking the strings. Just as aggression and anger could be transmitted to a sword, the right hand was for the majority of musicians the natural choice for emotional expression.
Attending a Saturday evening performance of Die Fledermaus during the 2006 – 2007 Lyric Opera season with my right arm in that rather conspicuous splint, I was only able to gesture by silently striking my right sleeve with my left hand, when the audience broke into enthusiastic applause after each aria. The phrase “What is the sound of one hand clapping?” came to mind. Originally posed as a Zen kōan or riddle by the Japanese master Hakuin Zenji (Ekaku), it appears in a work entitled Yabukōji composed in 1752. At that moment it seemed to me to be emblematic of the mystery of left-handedness. The mystery of left-handedness or sinistrality is part of a larger question: Why should handedness exist given that it violates the symmetry apparent in our upper extremities? Further, why does man so universally favor his right hand?
Before proceeding further, I am chastened by the cautionary words of the 19th century Scottish essayist, satirist, and historian Thomas Carlyle: “Why that particular hand [the right] was chosen is a question not to be settled, not worth asking except as a kind of riddle…”
From what source does our mental construct of left and right arise? “Left” and “right” are symbols, signifiers emerging as early as language itself. Using the tools of philology, we can trace these words back in time within language families. In most languages a single term signifies “right,” while “left” is either not found as in reconstructions of proto-Indo-European, or is often designated by multiple terms. Robert Hertz, a student of Émile Durkheim, in his 1909 essay, “The Pre-eminence of the Right Hand,” views the social constructs arising from “right” and “left” as part of the duality with which man orders his world. This refers to pairs of opposites such as male, female; strength, weakness; family, stranger; sacred, profane, etc. This duality is found in the archaeology of ancient cultures, the anthropology of contemporary native societies, the symbolism of Judaism and Christianity, and the philosophy of Aristotle. The near universal preference for the right hand and associated difference in skill provides a platform for the mythology constructed around “the left” and “the right” and the right hand and left hand in particular. In 1768 Immanuel Kant addressed the properties of “left” and “right” in an essay titled “Concerning the Ultimate Ground for the Differentiation of Directions in Space.” Quoting from that article:
Because of its three dimensions, physical space can be thought of as having three planes, which all intersect each other at right angles. --- One of these two vertical planes, divides the body into two externally similar halves, and furnishes the ground of the difference between the right and the left side. The other vertical plane, which also stands perpendicularly on the horizontal plane, makes possible the concept of the side in front and the side behind.
Since the distinct feeling of the right and the left side is of great necessity for judging directions, nature has established an immediate connection between this feeling and the mechanical organization of the body. In virtue of this organization, one side of the body, the right side, namely, enjoys an indisputable advantage over the other in respect of skill and perhaps strength, too.
Concerned with the representation of the three dimensions of space as perceived by an observer firmly rooted on the earth’s surface, Kant extends his inquiry to the question of “absolute space.” The existence of “absolute space,” Newton’s fifth law of motion, appears in the Principia, delivered to the Royal Society of London in 1687 almost a decade after Kant penned his essay. Kant reflects that the right side enjoys an indisputable advantage over the left and observes that “all peoples of the world are right-handed,” dismissively adding in parentheses, “(apart from a few exceptions which, like that of squinting, do not upset the universality of the regular natural order).”
Not so fast, Professor Kant, left-handedness is long and well established in human kind. We “can’t” (kant!) discuss the one without the other!
There is general agreement that approximately 13% of the human population can be characterized as left-handed, and conversely, 87% of the population declare themselves to be right-handed. This distribution is present across geographic ethnic and “racial” boundaries. A number of questions immediately follow. By what criteria do we measure handedness? Is it simply preference or ability? Is strength a factor, or does that develop as a result of preference? If queried, most individuals think of themselves as right- or left-handed, yet after a moment of thought, they might seek to modify their answer. A left-handed individual is more likely to be the one to want to qualify his preference than his or her right-handed counterpart. Gender does matter! Studies universally confirm that women are somewhat more apt to be right-handed than men, a phenomenon that begs a biological explanation. The scientists studying handedness, who seem to be primarily psychologists, use a standardized inventory of skills normally performed by one hand alone, such as throwing, writing, holding a racquet, or holding a toothbrush to establish and quantify the direction of handedness. In an attempt to look objectively at handedness, manual dexterity can be measured by various tests, such as the speed in placing a number of pegs into a series of holes on a test board. The results of these studies parallel those that look at preference. Along with a slight differential in strength between the two extremities, the results raise the question whether preference itself leads to skill rather than reflecting any innate difference. The entire subject becomes further complicated when we look at sidedness in general. This refers to eye preference, ear preference, and footedness, but may be extended to obscure preferences such as which thumb is uppermost when we clasp our hands. In short, these phenomena show less consistency and congruence with an individual’s handedness, and the issue has largely been sidestepped.
Is the frequency of left-handedness changing over time? Historical data suggest that left-handedness has been increasing over the last 150 years. Since these statistics are usually compiled on the basis of the hand preferred for writing, cultural prejudices influence their interpretation. Previous trends in elementary school education were apt to discourage youngsters attempting to write with their left hand and to achieve this end, at times resorted to draconian measures. The apparent rise in left-handedness is attributed to the cessation of such practices. Rigorous population studies are of relatively recent origin, commencing largely during the 20th century. In an effort to obtain meaningful data from the 19th century, investigators have often found ingenious approaches. Most recently, a collection of 826 cellulose nitrate film negatives taken in northern England between 1897 and 1913 were analyzed by Chris McManus and Alex Hatigan for the hand individuals chose to wave at the camera (do we really select our “dominant” hand when we wave?). The subjects in the photographs were also stratified according to their presumed age. The results suggest a steady increase in left-handed arm waving from 1841 to 1892, reaching 7.4% in the youngest cohort compared to 24% in a modern sample and supporting an apparent increase in left-handedness.
The subject of demographics would be incomplete without pausing to mention that if Senator Barak Obama wins the Democratic Party’s nomination, the next president of the United States will again be a lefty (in case you haven’t noticed, both he and Senator John McCain write with their left hand). Again! During the 20th century five out of the nineteen men to hold our highest office or 26% have been left-handed. Harry S. Truman, the 33rd president (Truman wrote with his right hand, but threw the opening pitch of the baseball season with his left arm); Gerald Ford, the 38th president; Ronald Reagan, the 40th president; George Herbert Bush, the 41st president; and William Jefferson Clinton, the 42nd president were all lefties. Chris McManus, in his highly recommended book Right Hand, Left Hand, analyzes these statistics further by pointing out that prior to 1900, James Garfield, our 20th president elected in 1881 and tragically assassinated that same year, was the only other known left-hander in our nation’s history. This brings the percentage down to the expected 13%, and when he extends the analysis to both presidents and their respective vice presidents (the latter presumably being equally fit to be president), the percentage drops to 9.2%.
How ancient is the dominance of right-handedness in our species? Stanley Coren and Clare Porac, while members of the Department of Psychology of the University of Victoria in British Columbia, tried to answer this question by surveying works of art that spanned 50 centuries, dating back to pre-3000 B.C.E. They found 1,180 instances of single-handed tool or weapon use. On average, the right hand was represented 93% of the time in every historical period and in every geographic area across the globe. In a separate survey of Egyptian art from the era of the pharaohs, human figures were characteristically depicted in a right profile view. Since it is more natural for right-handers to draw left profiles and conversely, for left-handers to draw the right profile, it was believed that the ancient Egyptians were left-handed. It is now felt that the preference for the right profile reflected the cultural belief that the right side was sacred and the left side profane. The frequency of right-handed tool usage depicted in ancient Egyptian art is comparable to modern society.
The Bible is a rich source for references to handedness, usually favoring the right hand or right side over the left. The first written record on the incidence of left-handedness comes from the book of Judges (20:15) and relates events occurring in the third generation after the Exodus from Egypt, or the 13th century B.C.E. The Benjaminite army is described as having a battalion of “seven hundred picked men from Gibeah, left-handed men, who could sling a stone and not miss by a hair’s breath.” Calculating the prevalence of left-handedness based on the size of the army, stated to be 26,000 men, a figure for left-handedness of 2.6% is obtained. Besides telling us that right-handedness was dominant at the time the book was written, the story is interesting in that the lefties were grouped together in a single battalion. The Benjaminites refer to the Israelite tribe of Benjamin, literally meaning “son of my right hand.”
Cave paintings of Cro-Magnon man dating from 30,000 to 40,000 years ago depict human hands that are predominantly the left hand. Assuming the artists most likely traced their own hand, it is concluded that they were most likely right-handed. Did right-handedness perhaps reach even further back in history to our earliest ancestors, Australopithecus, Homo erectus, and Homo habilis (notably “handy man”)? There are three lines of archaeological evidence supporting the predominance of right-handedness. Microwear analysis of flint tools and the manner by which they were knapped favors that the tools were generated by right-handed blows. Visualize the validation of these methods by graduate students assigned the task of mastering prehistoric tool- making skills. Fossil teeth presumed to be those of Australopithecus, approximately 2.5 million years old, display a pattern of dental wear suggesting that their owner was more likely to grasp meat or bones with the right hand. Finally, the dominant pattern of depressed skull fractures in fossil primates convinced anthropologist Raymond Dart that our ancestors used their right hand as they dealt their quarry a fatal blow. The late Stephen Jay Gould liked to imagine a Neanderthal man dressed in a business suit attracting little notice in the New York subway system. I might wish to embellish this portrait by suggesting that if you asked to look at his neatly folded copy of the New York Times he would most likely pass it to you with his right hand. There is, however, no evidence that the Neanderthals possessed spoken let alone written language.
Having established the prevalence of right-handedness and its antiquity among Homo sapiens, it is appropriate to ask if this trait is genetically determined.
Plato in the 5th century B.C.E. somewhat scornfully declared:
It is due to the folly of nurses and mothers that we have become limping, so to say, in our hands. For in natural ability the two limbs are almost equally balanced; but we ourselves by habitually using them in a wrong way have made them different.
Aristotle, one of the first biologists, in the 4th Century B.C.E. in his Magna moralia countered by stating that “however much we equalize the use of the two [...] Change of use does not abolish the natural distinction,” the implication being that the difference was inherited.
Charles Darwin returned to England in October 1836 after his historic five-year voyage on the HMS Beagle. It was on this voyage that he first conceived his ideas on evolution that would form the basis for his monumental work on The Origin of the Species. In January 1839 he married his cousin Emma Wedgwood and on December 27 his first child, William, was born. Darwin was thinking about child development before his son’s birth and created a notebook, “The Natural History of Babies” with a list of questions he felt needed answering. As early as 11 weeks of age, Darwin tried to determine the direction of his son’s handedness. He had good reason for making these observations, the infant’s mother and maternal grandfather, Josiah Wedgwood II, were left-handed. Left-handedness, Darwin would later comment, was “well known to be inherited.” This anecdote raises two separate issues. When during human development does handedness appear, and is there a genetic mechanism that determines its direction?
Hand preference in the human fetus has been studied by ultrasound examination. As early as 10 weeks into gestation, fetuses show a presumed preference for right arm movement. At this early stage of development, neurons from the brain have not yet connected to the spinal cord. The relevance of these observations to handedness is open to debate, but they raise the possibility that handedness arises at a lower level in the brain than the cerebral cortex. Testing the direction of handedness of children during the first two years of life is very difficult. Infants go through a “chaotic” stage when hand preference changes from day to day. Sometime around two years of age, the direction of handedness is declared and is set for life. Mastering the concept of right and left develops slowly, and recognition that right and left are reversed for the person one is facing takes most children well beyond the first decade of life to grasp. Difficulties with right from left, a condition termed “right-left blindness”, is not uncommon. Drill instructors in the Russian Imperial Army attempting to train poorly educated recruits resorted to tying a bundle of straw to the right ankle and a bundle of hay to the left and shouting: “Straw, hay, straw, hay …” Roman armies seem to have had similar problems and marched to “spear [right], shield [left], spear, shield...” Nor is this problem confined to the illiterate. Sigmund Freud related that when having to indicate whether a direction was right or left, he relied on making a brief writing gesture with his right hand to assure himself of the correct response.
The majority of observers accept the premise that heredity plays an important role determining handedness. There is a popular belief in Scotland that families with the surname Carr or Kerr are left-handed. Carr and Kerr come from the Gaelic caerr, meaning “awkward”. “ker-handed” and “carry-handed” are common terms for left-handedness. The Kerrs are described in an anonymous poem:
But the Kerrs were aye the deadliest foes
That e’er to Englishmen were known
For they were left-handed men
And ‘fence against them there was none.
It is further believed that they built their castles with “left-handed” or counterclockwise staircases, giving them a fencing advantage in staving off attackers. In A Left-Hand Turn Around the World, lefty author David Wolman journeys to Ferniehirst Castle in Jedburgh, Scotland, to verify the counterclockwise construction of the castle’s staircase built by Andrew Kerr in the 1500s.
The strongest evidence in support of heredity as a cause of handedness comes from analyzing the handedness of children as it relates to that of their parents. As an example, data on 73,000 individuals obtained by combining several surveys revealed that more than 90% of children born to right-handed parents were right-handed. If one of the parents was left-handed, the percentage of right-handed children decreased to 80%; and if both parents were left-handed, the percentage of their children that would be right-handed decreased further to 74%. To date, no gene or combinations of genes that determine handedness have been identified. In 1972, Dr. Marion Annett, a psychologist at the University of Leicester, first proposed a hypothetical “right shift” gene and suggested that human handedness might depend on two genetically based factors. Discussing this topic in his recent book From Hand to Mouth, the Auckland psychologist, Michael C. Corballis, asks us to imagine the “right shift” gene with two alternative forms, or alleles. “One allele might be called D, for “dextral”, because it codes for a shift of handedness distribution toward right-handedness, and the other might be called C, for “chance” because it leaves the direction of handedness to random influences.”(1) The model predicts that 12.5% of the population should be left-handed and this fits the observed epidemiologic data. Perhaps by chance, experimental findings that explain the leftward embryological development of the cardiovascular system lend plausibility to this model. It is a subject to which we will shortly return.
Those who doubt that genetic factors determine the direction of human handedness cite the lack of concordance in identical twin studies to bolster their argument. One would expect monozygotic (MZ) twins, sharing identical genetic material, to have 100% concordance in the direction of handedness. Studies of handedness in identical twins reveal that 80% exhibit concordance in the direction of handedness while 20% are discordant. It is however, not necessary that identical twins be alike in every trait believed to be under genetic control. It would be expected that identical (MZ) twins have a higher concordance in handedness than non-identical (dizygotic) twins, who are genetically like ordinary siblings. Studies analyzing this question reveal this is indeed the case supporting the argument that the findings in twin studies are consistent a genetic mechanism.
Beyond the need to clarify the role genetics plays in determining handedness, there is the question of why left-handedness persists. This has led to speculation that the genetic factors might confer what is termed a “heterozygote advantage.” An example is the increased resistance to malaria observed in carriers of the sickle-cell trait. The sickle cell gene as a recessive trait confers a selective advantage on the carrier that allows the gene to exist in a state of equilibrium in the population. This phenomenon is referred to by geneticists as “balanced polymorphism.” In Annett’s genetic model, individuals with both the “right shift” or “D” allele and the “Chance” or “C” allele, would behave as if they were “heterozygotes.” Before addressing the question of what selective advantage left-handedness or a “left-handed” trait might confer, we must try to understand what advantage is associated with right-handedness that allowed it to evolve as a dominant human trait not found in any other primate or more distant species (an exception seems to be certain parrots who mock us with their left-footedness).
Given the apparent symmetry of the left and right upper limbs, there is nothing that might lead us to prefer one over the other. To understand human handedness we must look more closely at what the science of neurology can tell us. The discovery that the cerebral hemispheres differ in their functions, what has come to be known as the laterality of the central nervous system, suggests the possibility that “laterality” and handedness are related. A leading investigator in this field, Michael C. Corballis, refers to our species as “the lopsided ape.”
It is fair to state that well into the middle of the 19th century, beyond descriptive neuroanatomy, little was understood of the brain’s function other than “the law of decussation.” This Hippocrates had recognized in observing that injury to one side of the brain resulted in paralysis on the opposite side of the body. To Giovanni Battista Morgagni, who published in 1761 at the age of 78 his landmark work, On the Seats and Causes of Disease as Indicated by Anatomy (commonly known by an abbreviated form of the original Latin title, De Sedibus), we owe the meticulously compiled patient histories and gross autopsy findings including examples of pathology on one side of the brain producing paralysis on the opposite side of the body. His contemporary, the Parisian François Pourfour du Petit, an anatomist and surgeon, observing that head wounds sustained in battle resulted in contralateral motor paralysis, completed the picture by accurately describing the pyramids, a prominence at the top of the spinal chord where two-thirds of the motor fibers from either side of the cerebral cortex cross over to the opposite side of the body.
Enter Franz Joseph Gall, his name, tarnished for purporting to predict personality and aptitude from cranial contours, is remembered in the annals of neuroscience for proposing that the brain was not a uniform mass and that different mental processes resided in specific locations. He believed that language was located in the frontal lobes, and his student Jean-Baptiste Bouillaud offered 500 francs as a reward to anyone who could find a patient proving his mentor’s contention. In 1861, at a meeting of the Society for Anthropology in Paris, a young surgeon, Paul Broca, heard these claims repeated and shortly thereafter was given the opportunity to study a patient who would canonize his name in the history of neuroscience.
Broca, born in Sainte-Foy-la Grande in 1824, was a brilliant student destined to become a professor of surgical pathology at the University of Paris and a pioneer in the study of physical anthropology. Within a few days of the meeting, he was asked to see a patient institutionalized in the Bicêtre Hospital suffering from severe cellulitis of his right leg. The man, Leborgne, was nicknamed Tan because Tan was the only utterance he was capable of making. Tragically, he was an epileptic who years earlier had developed weakness of the right side of his body and had gradually lost the capacity for speech. Ultimately he was institutionalized in Bicêtre. Tan died a few days later, and the autopsy Broca performed revealed cystic pathology in the left posterior portion of the frontal lobe of his brain. Recognizing that the pathology might be located in the area of the brain responsible for language, Broca was quick to demonstrate this specimen to his colleagues and preserved it in a mixture of alcohol and formaldehyde. Broca was to see a second patient, Lélong, an 83-year-old man whose daughter recounted that her father had suffered a stroke 18 months earlier which had resulted in the paralysis of the right side of his body and the loss of his ability to speak. When Broca saw the man, he had fallen, sustaining a hip fracture, and shortly thereafter died. Broca performed an autopsy and found damage in the same area of the left hemisphere where he had observed the abnormal findings in his patient Tan. The specimen was preserved and he again presented the findings to his colleagues at a meeting of the society. In addition to seeing Paris, a visitor to the Mussé Duputryn on the left bank, will be rewarded with the opportunity to view these specimens.
Broca’s findings were published in the Bulletins de la Société d’Anthropologie de Paris in a series of papers between 1861 and 1865, and he reported observing an additional 20 such patients over a two-year period. Identifying the location of a center in the brain controlling language, and the laterality of the central nervous system attracted considerable attention. As is often the case with great discoveries Gustave Dax, the son of a rural physician, Marc Dax came forward with the claim that his father had presented, but never published, similar findings at a medical conference in 1836 in Montpellier in a talk titled “Damage to the left half of the brain associated with forgetting the signs of thought.” Within a decade of Broca’s discovery, a German neurologist, Carl Wernicke, reported on a second area located in the temporal lobe of the left hemisphere that participated in the generation of language. The speech of individuals afflicted by damage to this area of the brain was grammatically correct, but without meaning.
Broca also noted the relationship between handedness and speech. He began to articulate the notion that control of speech in the left hemisphere was related to right- handedness. He speculated, “One can conceive that there might be a certain number of individuals in whom the natural pre-eminence of the convolutions of the right hemisphere reverses the order of the phenomenon which I have described.” The individuals were of course left-handers. Erroneously, this led to the formulation of “Broca’s rule,” that the cerebral hemisphere controlling speech was on the side of the brain opposite the preferred hand. But as more patients suffering from paralysis on one side of the body and loss of speech were analyzed, it became apparent that left-handedness was not the simple converse of right-handedness. A left-handed patient suffering a stroke that resulted in paralysis on the right side of his body might also lose his ability to speak, and conversely, paralysis on the left side of his body did not always result in the loss of speech as might have been predicted by Broca’s rule. During this period, the concept of a dominant left hemisphere controlling speech and handedness in the majority of individuals emerged.
With advances in neurosurgery during the first half of the 20th century, it became important in each patient to locate the side of the brain controlling speech so as to avoid impairment of speech occurring as a complication of surgery. A test developed at the Montreal Neurological Institute known as the Wada test provided the answer. The test entailed the intra-arterial injection of sodium amytal into the carotid arteries and hence to the left or right cerebral hemisphere. Based on the side of injection that momentarily suppressed the patient’s ability to speak, it was possible to predict the cerebral hemisphere that controlled language. These studies revealed that in 96% of right-handed patients, language was represented in the left hemisphere. The pattern in left-handed patients confirmed that they do not simply have their brains “wired backwards.” In 70% of left-handers, language was still represented in the left cerebral hemisphere. Of the remaining 30%, in approximately half the speech center was in the right hemisphere, and in the other half it was represented in both hemispheres. Since the publication of these results in 1960, noninvasive imaging tests including functional MRI (magnetic resonance imaging) have emerged for localizing the dominant hemisphere and centers of speech. The findings using these techniques remain consistent with the Wada test. Right-handedness was associated with left cerebral lateralization in 96% of individuals during silent word generation. Left-handers also lateralized to the left cerebral hemisphere in 76% and the remaining left-handers, displayed either bilateral activation of the speech centers or right cerebral activation.
Language is uniquely human. Vocal behavior, however, may have its origins as far back as 170 million years. Anurans, predecessors of frogs, were probably among the first vertebrates with vocal cords and, vocalization in present-day frogs appears to be under left cerebral control. Vocalization by songbirds, like human speech, is controlled primarily on the left side of the brain. Songbirds exhibit a critical period in their development when, if not exposed to birdsong, they will not learn to sing. Similarly, humans not exposed to language in childhood will never learn to speak properly. In passerine birds, chaffinches and canaries, singing is accomplished by an organ called the syrinx, analogous to the human larynx. The nerve that activates the syrinx arises directly from the left side of the brain. Transecting the nerve on the left side causes the bird to lose most of its song, while cutting the nerve on the right side has little effect.
Language may have begun with gestural communication. Right-handers and left-handers are observed to consistently gesture with their preferred hand while speaking. The close relationship between gesture and language is underscored through the study of the sign language of the deaf. “Signing”, the language of the deaf, is a true language with the grammar and nuances of spoken languages. For the deaf, a cerebrovascular accident that damages the speech center will impair the ability to sign in the same manner that it would affect spoken language. These observations might suggest a functional advantage in establishing the neural apparatus for language, speech, gesture, and handedness on the same side of the brain. Through natural selection, this advantage may have resulted in left cerebral dominance. It must be added that physiologic confirmation of such an advantage has not been documented.
There is a dark side to sinistrality leading back to the question of why the trait persists. A decreased survival of left-handers was reported in a series of studies published in the 1980s noting a virtual absence of left-handed individuals over the age of 80. Substantiating data was found in The Baseball Encyclopedia correlating the life span of players with their batting preference. Again, it has been argued that these differences were driven by a cohort factor reflecting earlier cultural bias against lefties. Similar associations have been reported with autoimmune illness, dyslexia, stuttering, and—dare I mention—proneness to injury (the hazard of living in a right-hander’s world). From an evolutionary perspective, even a slight survival advantage for right-handedness would have been expected to lead to an extinction of left-handedness.
Left-hemispheric dominance is present in 70% of left-handers. Could it be that the mixed cerebral organization seen in the remaining 30% of lefties confers special attributes that in a Darwinian sense are “sexy”? Michael C. Corballis, a lefty himself, sees the answer in what he labels “magical ideation.” This refers to phenomena like extrasensory perception, spirituality, and possibly creative thinking. Analyzing “magical ideation” as a function of handedness, Corballis has found that magical thinking correlates significantly with mixed handedness and hence mixed cerebral organization or “cerebral indecision.” He asks where should we locate Albert Einstein? From photographs, he appears to have been a right-hander, but he was slow to speak as a child. Einstein was not mute in expressing his reasoned belief in a higher being and fond of challenging the theories of quantum mechanics saying, “God does not play dice with the universe.” There is a significant body of scientific literature on the functions of the right and left cerebral cortex, but a conclusive picture has yet to emerge that would allow us to answer these questions without veering perilously into the realm of pop psychology.
Pondering the role the association of right-handedness, speech, and right cerebral dominance played in our evolutionary history, while intriguing, does not bring us closer to the biologic mechanisms operative in determining right- or left-handedness. Can the body tell left from right? Beneath the apparent symmetry of our body, there is marked asymmetry under the surface. Our hearts, and those of primates as well as the entire family of vertebrates, are uniformly located on the left side of the chest. The liver and gall bladder reside on the right side of the abdomen, while the spleen hides in the upper left corner of the abdomen shielded by the ribcage. The left and right lungs are dissimilar, and these organs are supplied by a circulatory system that has adapted to this asymmetry. Early in embryological development these organs arise from a midline structure, and something directs their migration to the left or right. If we say that the “something” is genetically determined, much as it would be desirable to isolate the genetic loci that are operative, our understanding is no further advanced than if we say that a complicated building arises from a blueprint. Situs inversus is a human anomaly affecting the above organs so that they appear as if they developed in Alice’s “looking-glass world.” The anomaly occurs in one of every 8,000 to 25,000 people who otherwise lead normal lives. Before the discovery of x-rays and the electrocardiogram, situs inversus went undetected in life only to be discovered at autopsy. Incidentally it is not associated with an increased frequency of left-handedness.
Animal studies on the leftward migration of the heart have shed light on how such anomalies occur. Specific proteins with somewhat fanciful names—for example, Sonic hedgehog, Nodal and Lefty—make their appearance on the left and right side of the primordial circulatory system at critical moments in ontogenesis crucial to the proper orientation of the developing heart. In 1998, while studying the cardiac nodal cells of mice embryos under scanning microscopy, Nobutaka Hirokawa and his colleagues at the University of Tokyo were surprised to discover that the nodal cells possessed cilia (tiny filaments) that were rotating in a counterclockwise motion and capable of sweeping these proteins to the left, thereby inducing the leftward growth of the developing heart. Paralyzing the rotation of these cilia experimentally, results in the mice whose cardiovascular system develops to the left or right of the embryo with equal frequency. The findings help explain a rare human illness, Kartagener’s syndrome. Individuals with this syndrome are prone to respiratory illness because the cells lining their respiratory tract lack the normal ciliary function necessary for the clearance of bacteria. Men suffering from the syndrome are infertile; the tails of their sperm are immobile and incapable of fertilization. Most important for our discussion, 50% of patients with Kartagener’s syndrome have situs inversus. It is here that Annett’s concept that the C or Chance allele that determines left-handedness, gains biological plausibility. Christopher McManus, professor of psychology and medical education at University College London and author of the book, Right Hand, Left Hand, sees the path to a deeper understanding of right-handedness and left cerebral dominance arising at a molecular level. He may be mixing apples and oranges when he asks whether the counterclockwise rotation of the cilia might be related to the fact that their structural proteins are made of L (or levo)-amino acids rather their mirror image molecules D-amino acids. L-amino acids are the most abundant forms on earth in the areas where life evolved.
Perhaps it is best to recall the admonition of Thomas Carlyle: “Why [the right hand] was chosen is a question not to be settled, not worth asking except as a kind of riddle...” I feel his presence over my left shoulder tonight and hope he is impressed with how much has been learned. Perhaps he will relent and agree that it might yet be settled. While it remains a riddle, I hope he has been convinced it is well worth asking.
The author wishes to acknowledge the important contribution to his thoughts on this subject found in the excellent book by Chris McManus, Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms, and Cultures and two equally fascinating books written by Michael C. Corballis, From Hand To Mouth: The Origins of Language and The Lopsided Ape: Evolution of the Generative Mind. I would like to call to your attention to an excellent book, Piano Music for One Hand, written by the Chicago pianist Theodore Edel. Special thanks to my good friend, Richard Salant, Ph.D., Distinguished Professor of Mechanical Engineering, Georgia Institute of Technology for calling my attention to the Web site “Piano Music for the Left Hand Alone” (hjem.get2net.dk/Brofeldt). I have also enjoyed the opportunity to discuss this topic with two of my good friends the geneticist and hematologist Henri Frischer, M.D., Ph.D., and the head of neuroradiology at Rush University Medical Center, Michael S. Huckman, M.D.
- Michael C. Coballis. From Hand to Mouth: The Origins of Language. P.172, Princeton University Press, Princeton, N.J., 2002.
, MD is a gastroenterologist and Associate Professor Emeritus at Rush University Medical Center. He is also a member of our Editorial Board and serves as the President of Hektoen's Society of Medical History & Humanities.