The right hand

by Sir Daniel Wilson

The theory of Dr. Barclay, the celebrated anatomist, is thus set forth by Dr. Buchanan, from notes taken by him when a student: “The veins of the left side of the trunk and of the left inferior extremity cross the aorta to arrive at the vena cava; and some obstruction to the flow of blood must be produced by the pulsation of that artery.” To this Dr. Barclay traced indirectly the preferential use of the right side of the body, and especially of the right hand and foot “All motions,” he stated, “produce obstruction of the circulation; and obstruction from this cause must be more frequently produced in the right side than the left, owing to its being more frequently used. But the venous circulation on the left side is retarded by the pulsation of the aorta, and therefore the more frequent motions of the right side were intended to render the circulation of the two sides uniform.” The idea, if correctly reported, is a curious one, as it traces right-handedness to the excess of a compensating force for an assumed inferior circulation pertaining naturally to the right side; and incidentally takes into consideration an abnormal modification affecting the development or relative disposition of organs. Both points have been the subject of more extended consideration by subsequent observers. It is curious, indeed, to notice how physiologists and anatomists have shifted their ground, from time to time, in their attempts at a solution of what has been very summarily dismissed by others as a very simple problem; until, as Dr. Struthers remarks, it “has ceased to attract the notice of physiologists only because it has baffled satisfactory explanation.”

The eminent anatomist, Professor Gratiolet, turned from the organs in immediate contact with the arm and hand, and sought for the source of right-handedness in another and truer direction, though he failed to realise its full bearings. According to the Professor, in the early stages of fœtal development the anterior and middle lobes of the brain on the left side are in a more advanced condition than those on the right side, the balance being maintained by an opposite condition of the posterior lobes. Hence, in consequence of the well-known decussation of the nerve roots, the right side of the body,—so far as it is influenced by brain-force,—will, in early fœtal life, be better supplied with nervous force than the left side; and thereby movements of the right arm would precede and be more perfect than those of the left. The bearings of this line of argument in its full compass will come more fitly under review at a later stage.

Dr. Andrew Buchanan, Professor of Physiology in the University of Glasgow, in a paper communicated by him to the Philosophical Society of Glasgow in 1862, entitled “Mechanical Theory of the predominance of the right hand over the left; or more generally, of the limbs of the right side over those of the left side of the body,” aimed at a solution of the question in a new way. According to him, “the preferential use of the right hand is not a congenital but an acquired attribute of man. It does not exist in the earliest periods of life.” Nevertheless, “no training could ever render the left hand of ordinary men equal in strength to the right;” for “it depends upon mechanical laws arising out of the structure of the human body.” This theory is thus explained: In infancy and early childhood there is no difference in power between the two sides of the body; but so soon as the child becomes capable of bringing the whole muscular force of the body into play, “he becomes conscious of the superior power of his right side, a power not primarily due to any superior force or development of the muscles of that side, but to a purely mechanical cause. He cannot put forth the full strength of his body without first making a deep inspiration; and by making a deep inspiration, and maintaining afterwards the chest in an expanded state, which is essential to the continuance of his muscular effort, he so alters the mechanical relations of the two sides of his body that the muscles of his right side act with a superior efficacy; and, to render the inequality still greater, the muscles of the left side act with a mechanical disadvantage.” Hence the preference for the right side whenever unusual muscular power is required; and with the greater exercise of the muscles of the right side their consequent development follows, until the full predominance of the right side is the result.

This theory is based not merely on the preponderance of the liver and lungs on the right side, but on these further facts: that the right lung is more capacious than the left, having three lobes, while the left has only two; that the liver, the heaviest organ of the body, is on the same side; and that the common centre of gravity of the body shifts, more or less, towards the right, according to the greater or less inspiration of the lungs, and the consequent inclination of the liver resulting from the greater expansion of the right side of the chest. Herein may possibly lie one predisposing cause leading to a preferential use of the right side. But the evidence adduced fails to account for what, on such a theory, become normal deviations from the natural action of the body. The position of the liver and the influence of a full inspiration combine, according to Dr. Buchanan, to bring the centre of gravity of the body nearly over the right foot. Hence in actively overcoming a resistance from above, as when the carter bears up the shaft of his cart on his shoulder, the muscular action originates mainly with the lower limb of the same side, which partakes of the same muscular power and development as the corresponding upper limb. On all such occasions, where the muscular action is brought directly into play in overcoming the weight or resistance, Dr. Buchanan affirms that the right shoulder is much more powerful than the left, but in the passive bearing of weights it is otherwise. The very fact that the centre of gravity lies on the right side gives a mechanical advantage in the use of the left side in sustaining and carrying burdens; and this assigned pre-eminence of the left side and shoulder, as the bearer of burdens, is accordingly illustrated by means of an engraving, representing “a burden borne on the left shoulder as the summit of the mechanical axis passing along the right lower limb.”

In the year following the publication of Dr. Buchanan’s Mechanical Theory, Dr. John Struthers, Professor of Anatomy in the University of Aberdeen, communicated to the Edinburgh Medical Journal a paper, “On the relative weight of the viscera on the two sides of the body, and on the consequent position of the centre of gravity to the right side.” In this he shows that the viscera situated on the right side of the medial line are on an average 22·75 oz. av. heavier than those on the left side. The right lung, in the male, weighs 24 oz., the left 21, giving a preponderance of 3 oz. in favour of the right. The average weight of the heart, in the male, is 11 oz. But the left side is not only the larger, but the thicker, and as the result of careful experiments by Dr. Struthers, he assigns to the right side a full third of the weight of the heart, or 3¹⁄₂ oz. for the right, and 7¹⁄₂ for the left side. Other viscera are estimated in like manner, with the result from the whole that the centre of gravity of the body, so far as it depends on their weight and position, is nearly three-tenths of an inch distant from the medial plane towards the right side. As a physical agent constantly in operation in the erect posture, Dr. Struthers states that this cannot but exert an influence on the attitudes and movements of the body and limbs; and he accordingly indicates his belief that this deviation of the centre of gravity furnishes the most probable solution of the causes “of the preference of the right hand by all nations of mankind.”

The value of Dr. Struthers’s determination of the exact weight and relative eccentricity of the viscera on the two sides of the body was fully recognised by Dr. Buchanan; and in a communication to the Philosophical Society of Glasgow in 1877 he stated that he had been led to greatly modify his earlier opinions. He had, as shown above, ascribed the predominance of the right hand over the left to the mechanical advantage which the right side has in consequence of the centre of gravity inclining to it. But he says in his later treatise, “I judged hastily when I inferred that this is the ground of preference which prompts the great majority of mankind to use their right limbs rather than their left. The position of the centre of gravity on the right side is common to all men of normal conformation, and furnishes to all of them alike an adequate motive, when they are about to put forth their full strength in the performance of certain actions, to use the limbs of the right side in preference to those of the left. But such actions are of comparatively rare occurrence, and the theory fails to explain why the right limbs, and more especially the right hand, are preferred on so many occasions where no great muscular effort is required; and fails still more signally to explain why some men give a preference to the limbs of the left side, and others manifest no predilection for either.” Dr. Buchanan accordingly proceeds to show that there is not only the element of the position of the centre of gravity as the pivot on which all the mechanical relations of the two sides of the body turn; but there is, as he conceives, this other and no less important element. “The centre of gravity situated on the right side is variously placed upwards or downwards, according to the original make or framework of the body.” In the great majority of cases this lies above the transverse axis of the body, with a consequent facility for balancing best, and turning most easily and securely on the left foot, with the impulsive power effected by the muscles of the right lower limb. Man is thus, as a rule, right-footed; and, according to Dr. Buchanan, by a necessary consequence becomes right-handed. By a series of diagrams he accordingly shows the assumed variations: (1) the centre of gravity above the transverse axis, with its accompanying right-handedness; (2) the centre of gravity corresponding with the transverse axis, which he assigns to the ambidextrous; and (3) the centre of gravity below the transverse axis begetting left-handedness. The whole phenomena are thus ascribed to the instinctive sense of equilibrium, which constitutes a nearly infallible guide in all the movements of the human body. The greater development of the organs of motion of the right side is therefore, as he conceives, not congenital, but arises solely from the greater use that is made of them. The relative position of the centre of gravity depends accordingly on the original conformation of the body. Broad shoulders, muscular arms, a large head and a long neck, all tend to elevate the centre point; while the contrary result follows from width at the haunches and a great development of the lower limbs.

The intermediate condition, in which the centre of gravity falls upon the transverse axis, with no instinctive tendency to call into action the muscles of the one side of the body in preference to those of the other, constitutes, according to Dr. Buchanan, the most happy conformation of the body. “It belongs,” he says, “more especially to the female sex. It is this that so often renders a young girl a perfect model of grace and agility. It is the same conformation that enables the ballet-dancer to whirl round on her one foot till the spectators are giddy with looking at her, when she completes her triumph by revolving with the same ease and grace on her other foot also.” He further adds: “If accurate statistics could be obtained, I believe it would be found that while a very great majority of males are right-handed, the proportion of females is less; and that, on the contrary, a larger proportion of females than of males are ambidextrous or left-handed.”

Consistently with the ideas thus set forth, both Dr. Buchanan and Dr. Struthers regard right-handedness as an acquired habit, though under the influence and control of the mechanical forces indicated by them. “As the question,” says the latter, “in so far as it can bear on the cause of the preference of the right hand, must turn on the weight and position of the viscera in the child at the period when the predominance of the right hand is being gradually developed, in the second and third years, and afterwards, it is necessary to make the calculation from the facts as presented in children.” In a letter to myself he thus writes: “I have again and again verified the fact in my own children, that in early childhood there is no preference for one hand more than the other.” But this, as has been already shown, may be partly due to modes of nursing and other temporary causes affecting the child in its first infantile stage; and though it may undoubtedly be affirmed of many, if not indeed of the majority, of children at that stage: a certain number will be found to manifest a distinct preference, at a very early age, for one or the other hand. In the case of a niece of my own, the left-handedness showed itself very soon; and in my grandson it was independently observed by his mother and nurse, and brought under my notice, that so soon as he was able to grasp an object and transfer it from one hand to the other, he gave the preference to the left hand. A like decided preference for the right hand, though doubtless also comparatively rare, is more frequent; and the farther research is carried, the more manifest does it appear that—whatever be the originating cause,—the preferential use of what we designate the right hand is instinctive with a sufficiently large number to determine the prevalent usage; while with a smaller number an equally strong impulse is felt prompting to the use of the left hand, in defiance of all restraining influences. It is indeed always necessary to give full weight to the influences of education, the whole tendency of which, from early childhood, operates in one direction. The extent to which this is systematically employed to develop the use of the one hand at the expense of the other, is illustrated by the conventional rules for the use of the knife and fork. It is not sufficient that the knife shall be invariably held in the right hand. The child is taught to hold his knife in the right hand and his fork in the left when cutting his food; but when either the fork or spoon is used alone, it must forthwith be transferred to the right hand. All voluntary employment of the left hand in any independent action is discountenanced as awkwardness or gaucherie; and thus, with a large majority, especially among the more refined and conventional classes of society, it is rendered a comparatively useless member, employed at best merely to supplement the other.

Reference has already been made to more or less definite allusions to an exceptional prevalence of left-handedness in the Punjab, and among the Sandwich Islanders, the Hottentots, and South African Bushmen; but they rest apparently on very partial and limited observations. So far as appears, it may be confidently assumed that left-handedness is little more prevalent among the rude and uncultured classes of society, or among savage than civilised races; as would certainly be the case if right-handedness mainly depended on an acquired habit. The Rev. George Brown, who has spent upwards of fourteen years as a missionary among the Polynesians, informs me that left-handedness is as rare among the natives of the Pacific Islands as with ourselves; while in all their languages the distinction is clearly indicated. Dr. Rae, whose own inveterate left-handedness was calculated to draw his attention to its manifestation among the Indians and Eskimos with whom he was brought into prolonged contact, only noticed such an amount of ambidextrous facility as is naturally developed in the paddler, the trapper, and lumberer, in the exigencies of forest and hunter life. A similar opinion was expressed to me by Paul Kane, whose wanderings as an artist among the tribes of British North America gave him exceptional facilities for observation; and this conclusion accords with the experience of members of the Canadian Geological Survey.

Turning next to the idea set forth by Dr. Buchanan as to the greater preponderance of ambidexterity or left-handedness among females, the results of my own observation by no means tend to confirm this. I have already noted the case of a lady whose left-handedness is accompanied by great dexterity. I have repeatedly met with cases of ladies who use the needle skilfully with the left hand; but the results of inquiries addressed to musicians and music teachers indicate that in the great majority of cases the cultivation of the left, as the weaker or less skilful hand, has to be sedulously enforced in the training of the female organist and pianist. It is because left-handed pianists are rare that their exceptional dexterity is noted, as in the case of a Canadian lady referred to above: “She had great advantages from her left-handedness. She was a very good performer on the piano, and her bass was magnificent.”