The remarkable difference in the convolutions of different brains, and the consequent extent of superficies of some brains over others apparently of the same size, have been matter of special observation, with results lending confirmation to the idea that great development of the convolutions of the brain is the concomitant of a corresponding manifestation of intellectual activity. But the complexity in the arrangement of these convolutions, and the consequent extent of superficies, often differ considerably in the two hemispheres of the same brain. The variations in shape and arrangement of the convolutions in either hemisphere may be no more than the accidental folds of the cerebral mass, in its later development in the chamber of the skull; and within ordinary limits they probably exercise no appreciable influence on physical or mental activity.
In so far as right-handedness is a result of organic structure, and not a mere acquired habit, some trace of it should be found in the lower animals, though in a less degree. Dr. Buchanan, in discussing his Mechanical Theory, notes that, “while the viscera of the quadruped have the same general lateralised position as in man, there is a reason why this should be carried to a greater extent in man than in the quadruped, owing to the much greater lateral development of the chest and abdomen of the human figure, in order to adapt it to the erect posture, as contrasted with the great lateral flattening of the trunk in quadrupeds. The equipoise is therefore more disturbed in man than in the quadruped.” In the case of the monkey, its necessities as a climber no doubt tend to bring all its limbs into constant use; but, possibly, careful study of the habits and gestures of monkeys may disclose, along with their ambidextrous skill, some traces of a preference for the limbs on the one side. The elephant has been repeatedly affirmed to betray a strongly marked right-sidedness; and this is reiterated in a communication by Mr. James Shaw to the Anthropological section of the British Association, where he notes the “curious fact that elephants have been frequently known to use the right tusk more than the left in digging up roots, and in doing other things.” But the statement is vague, and, even if confirmed by adequate proof, can scarcely be regarded as the equivalent of right-handedness. In dogs it may be noticed that they rarely move in the direct line of their own body, but incline to one side or the other, the right hind-foot stepping into the print of the left fore-foot, or vice versâ. In the horse, as in other quadrupeds, a regular alternation in the pace is manifest, except when modified by education for the requirements of man. I experienced no difficulty in teaching a favourite dog to give the right paw; and no child could more strongly manifest a sense of shame than he did when reproved for the gaucherie of offering the wrong one. The saddle horse is trained to prefer the right foot to lead with in the canter; while the same animal is educated differently when destined for a lady’s use; but I have been informed by two experienced veterinary surgeons that, while some horses learn with very slight training to start with the right foot, others require long and persevering insistency before they acquire the habit. A curious relation between man and the lower animals in the manifestation of the organic influences here noted is indicated by a writer in the Cornhill Magazine, when, referring to the well-ascertained fact that aphasia is ordinarily accompanied with disease of the right side of the brain, he says: “Right-sidedness extends to the lower races. Birds, and especially parrots, show right-sidedness. Dr. W. Ogle has found that few parrots perch on the left leg. Now parrots have that part at least of the faculty of speech which depends on the memory of successive sounds, and of the method of reproducing such imitation of them as a parrot’s powers permit; and it is remarkable that their left brain receives more blood and is better developed than the right brain.” The same writer expresses his doubt as to monkeys showing any tendency to right-handedness; but with the constant use and training of the hands by the Quadrumana in their arboreal life, opportunities for the manifestation of any instinctive preference for either hand must be rare; and is likely to elude all but the most watchful observers.
A paper was communicated by Dr. Delaunay to the Anthropological Society of France, on the subject of right-handedness. I only know of it by an imperfect notice, in which he is reported to look on the preferential use of the right hand as a differentiation arising from natural selection, while he regards ambidexterity as a mere “survival.” But Dr. Pye-Smith long ago remarked that “it is clear that in the progress of civilisation one or other hand would come to be selected for the more characteristic human actions for which only one is necessary, such as wielding a pen or other weapon;” but he recognises the insufficiency of the suggestion, and adds in a footnote: “The difficult point is to guess by what process the right rather than the left hand has been so universally preferred.” He then glances at possible guidance to be derived from the study of the habits of savage tribes, though still the old difficulty recurs; and he thus proceeds: “In default of any better suggestion, might one suggest an hypothesis of the origin of right-handedness from modes of fighting, more by way of illustration than as at all adequate in itself? If a hundred of our ambidextrous ancestors made the step in civilisation of inventing a shield, we may suppose that half would carry it on the right arm and fight with the left, the other half on the left and fight with the right. The latter would certainly, in the long run, escape mortal wounds better than the former, and thus a race of men who fought with the right hand would gradually be developed by a process of natural selection.” The recognition of the shield-hand, and the passive functions assigned to it, has already been referred to as one familiar to the ancient Greek and Roman, and no doubt to other and earlier nations. But here it is diverted to the service of one of the latest aspects of evolutionary development, and becomes the begetter instead of the product of left-handedness. To this idea of right-handedness as one of the results of a survival of the fittest, Dr. Delaunay adds the statement, professedly based on facts which he has accumulated, that ambidexterity is common among idiots. The results noted probably amount to no more than the negative condition of general imbecility, in which the so-called ambidexterity of the idiot involves, not an exceptional skill in the left hand, equalising it with the right, but only a succession of feeble and often aimless actions manifesting an equal lack of dexterity in either hand. Where left-handedness is strongly developed, it is, on the contrary, not only accompanied with more than average dexterity in the organ thus specialised, but also with a command of the use of the right hand, acquired by education, which gives the individual an advantage over the great majority of right-handed men. The surprise occasionally manifested at any display of dexterity by left-handed performers, as though it were accomplished under unusual disadvantages, is altogether unjustified. In reality, a strongly developed left-handedness is, equally with a strongly developed right-handedness, an indication of exceptional dexterity. Such skill as that of the left-handed slingers of the tribe of Benjamin is in no way exceptional. All truly left-handed, as well as all truly right-handed persons, are more likely to be dexterous than those who are unconscious of any strong impulse to the use of either hand. The bias, whether to the right or the left, is, I feel assured, the result of special organic aptitude. With the majority no well-defined bias betrays any unwonted power, and they merely follow in this, as in so much else, the practice of the predominant number. But there is no such difference between the two hands as to justify the extent to which, with the great majority, one is allowed to become a passive and nearly useless member. The left hand ought to be educated from the first no less than the right, instead of leaving its training to be effected, imperfectly and with great effort, in later life, to meet some felt necessity.
Dr. Brown-Sequard, in one of his latest discussions of the closely related, though much more comprehensive question, “Have we two brains?” remarks: “We have a great many motor elements in our brain and our spinal cord which we absolutely neglect to educate. Such is the case with the elements which serve for the movements of the left hand. Perhaps fathers and mothers will be more ready to develop the natural powers of the left hand of a child, giving it thereby two powerful hands, if they believe, as I do, that the condition of the brain and spinal cord would improve if all their motor and sensitive elements were fully exercised.” Without entering on the discussion of the larger question of the specific duality of the brain, experience shows that wherever the early and persistent cultivation of the full use of both hands has been carried out, the result is greater efficiency, without any counterbalancing defect. Under no enforcement of a violation of his innate impulses does the left-handed person ever exchange hands. He acquires an educated right hand and retains the dexterity of the left. In those cases where, by reason of injury or disease, the sufferer is compelled to resort to the neglected hand even late in life, it proves quite possible to train it to sufficient aptitude for all ordinary requirements. It is therefore obviously the duty of parents and teachers to encourage the habitual use of both hands; and in the case of manifest left-handedness, to content themselves with developing the free use of the right hand without suppressing the innate dexterity of the left. My own experience, as one originally left-handed, is that, in spite of very persistent efforts on the part of teachers to suppress all use of the left hand, I am now thoroughly ambidextrous, though still with the left as the more dexterous hand. I use the pen in the right hand but the pencil in the left; so that, were either hand disabled, the other would be at once available for all needful operations. Yet at the same time the experience of a long life assures me that scarcely any amount of training will suffice to invest the naturally sinister hand, whether it be the right or the left, with the dexterity due to innate, congenital, and therefore ineradicable causes. Nevertheless we are bimanous in the best sense, and are meant to have the free unrestrained use of both hands. In certain arts and professions both hands are necessarily called into play. The skilful surgeon finds an enormous advantage in being able to transfer his instrument from one hand to the other. The dentist has to multiply instruments to make up for the lack of such acquired power. The fencer who can transfer his weapon to the left hand, places his adversary at a disadvantage. The lumberer finds it indispensable in the operations of his woodcraft to learn to chop timber right and left-handed; and the carpenter may be frequently seen using the saw and hammer in either hand, and thereby not only resting his arm, but greatly facilitating his work. In all the fine arts the mastery of both hands is advantageous. The sculptor, the carver, the draftsman, the engraver, and cameo-cutter, each has recourse at times to the left hand for special manipulative dexterity; the pianist depends little less on the left hand than the right; and as for the organist, with the numerous pedals and stops of the modern grand organ, a quadrumanous musician would still find reason to envy the ampler scope which a Briareus could command. On the other hand, it is no less true that, while the experience of every thoroughly left-handed person shows the possibility of training both hands to a capacity for responding to the mind with promptness and skill: at the same time it is apparent that in cases of true left-handedness there is an organic specialisation which no enforced habit can wholly supersede.
Having determinately arrived at the conclusion that the source of right-handedness, and so of the exceptional occurrence of left-handedness, is to be sought for in the preponderant development of one or other hemisphere of the brain, and that, therefore, the test has to be sought in the examination of the brains of persons of exceptional dexterity, whether in the use of their right or left hand, the difficulty has been to obtain the desired objects of study. A considerable number of observations are desirable; and those can only be gradually accumulated as opportunities present themselves to observant students. As already noted, men of the first eminence have differed on the question of the greater weight of the left than of the right cerebral hemisphere; nor does a study of the ordinary manifestations of right-handedness encourage us to expect a very marked difference in the cerebral hemispheres in the majority of men. It need not therefore surprise us to find so able and experienced an observer as Dr. Thurnam reviewing the data published by Boyd, Brown-Sequard, and Broca, and expressing as his final conviction that further careful observations are needed before the general preponderance of the left hemisphere over the right can be accepted as an established truth.
As already noted, Dr. Boyd gives as the result of his observations on upwards of 500 human brains, that the weight of the left hemisphere almost invariably proved to be in excess of that of the right. In forty cases Dr. Broca found similar results, and observers of less note confirm them; so that but for the eminent authorities by whom those conclusions have been challenged, it would seem presumptuous to refuse them acceptance. But, countenanced by this conflict of opinion, it may be permissible to review the question in the narrower aspect of the present inquiry. Testing it then by a reverse process, and assuming hypothetically that the exceptionally dexterous right-handed man will be found to have the left hemisphere the heavier, and the true left-handed man vice versâ, the results arrived at by Dr. Boyd are altogether in excess of what might be anticipated. The number of the exceptionally dexterous right-handed, with an invincible instinctive preference for the use of that hand, though large in comparison with the no less dexterous left-handed, are nevertheless a minority. Habit, social usage, and education in all its forms, in the school, the drawing-room, the workshop, in all the arts of peace, and in nearly every operation of war, have so persistently fostered the development of the favourite hand that it is scarcely possible to arrive at any reliable statistics in proof of the initial proclivities of the large majority of conformists. Only a prolonged series of observations such as those already noted by Professor Baldwin, made at the first stage of life, and based on the voluntary and the unprompted actions of the child, can supply the needful data. But the careful observations of many years, prompted by a desire to master the source of an exceptional instinctive habit, have convinced me that the bias towards the preferential use of either hand in many, probably in the majority of cases, is slight. It is sufficient to lead to their following the practice of the determinately right-handed majority, but would not in itself present an obstacle to conformity to any prevalent usage, or to the influence of education. If then the preference of either hand furnishes any index of the relative development of the two cerebral hemispheres, what we may reasonably look for is a certain considerable percentage of brains with the weight of the left hemisphere in excess; a small percentage equally definitely characterised by the preponderance in the right hemisphere; while in the average brain the difference will be so slight as to be apt to escape observation. It is further to be noted that if the habitual use of the right hand tends in any degree to stimulate the development of the left cerebral hemisphere, then the examples of strongly-marked cases of such must greatly exceed those of the reverse type; since the left-handed man is almost invariably ambidextrous, and so subjects both hemispheres to the frequent stimulus of efferent nerve-force.
If the attention of physiologists devoted to cerebral investigations is specially turned to the present aspect of research, cases of well-marked left-handed patients, or what is manifestly of even greater significance, of exceptionally dexterous right-handed patients, in hospitals, asylums, and gaols, will from time to time present themselves. It has indeed been affirmed that left-handedness prevails among the “light-fingered” experts who find frequent lodging in our gaols. The statement rests on no basis of statistical evidence; but I can readily imagine that a left-handed pickpocket turning his exceptional dexterity to account, might find at times the same advantage that Ehud, the son of Gera the Benjamite, derived from using the hand ordinarily recognised as passive or inert. As to the more daring burglar, his sinister dexterity fills peaceful householders with trepidation as soon as the rumour transpires of his presence in their midst. In reality, however, the fancied prevalence of left-handedness among savages, criminals, and idiots, is a mere reflex of the long prevalent misconception that the preferential use of the left hand is solely due to acquired habit, incurable awkwardness, and incapacity. This is an idea that has often checked the development of exceptional dexterity and a full command of both hands.
Meanwhile it is only in so far as the hand may prove to be an index of the brain that observation is possible on the living subject. If the transposition of the viscera, and the exceptional pressure of the heart on the right, instead of the left side, were the source or the unvarying concomitant of left-handedness this could be tested with ease on the living subject. But the brain is beyond our reach; though pathological phenomena, along with the results of vivisection in the study of lower animal life, have thrown a flood of light on its functions; as well as on the localisation of specific cerebrations in their relation to sense, to language, and to general perceptions as elements of mental action.
A monograph on left-handedness, ultimately printed in the Proceedings of the Royal Society of Canada for 1886, was long delayed, in the hope of meeting with some response to appeals I had repeatedly addressed to medical friends, in the expectation that, sooner or later, some strongly-marked case of left-handedness among hospital or other patients might afford an opportunity for securing an autopsy of the brain. But unless the fact has been previously noted, there is little occasion in the passive condition of mortal disease to give prominence to the left-handed action of a patient, and I had to rest content with inviting attention to the subject when a favouring opportunity presented itself. But my anticipations of the result to be looked for were very definite, could the required organ of exceptionally developed nerve-force be got hold of. There was indeed one very suitable brain close at hand, and available for many curious speculative researches; but wholly beyond reach of ocular investigation by me. I could therefore only draw attention to it as possibly accessible to some future investigator, since even vivisection must needs defeat my aim. I accordingly remarked: “My own brain has now been in use for more than the full allotted term of threescore years and ten, and the time cannot be far distant when I shall be done with it. When that time comes, I should be glad if it were turned to account for the little further service of settling this physiological puzzle. If my ideas are correct, I anticipate as the result of its examination that the right hemisphere will not only be found to be heavier than the left, but that it will probably be marked by a noticeable difference in the number and arrangements of the convolutions.”
Happily since then the long-coveted opportunity has been afforded me. In February 1887 I learned from Dr. Daniel Clark, Superintendent of the Provincial Asylum at Toronto, of the death of Thomas Neilly, a patient who had been under the doctor’s care for nearly two years. He was a native of Ireland, had served in the army, and was there noted as so inveterately left-handed that he was placed on the extreme left of his company, and allowed the exceptional usage of firing from the left shoulder. He could read and write, and was considered a man of good intelligence, till he attained his thirty-fourth year, when symptoms of insanity manifested themselves, and he was removed to the asylum, where he died. My colleague, Professor Ramsay Wright, accompanied me to the asylum on my learning of his death. The brain was removed and the two hemispheres carefully weighed. Cerebral disease manifested itself in the evidence of softening of the brain. But it was fully available for the special inquiry; and the result of the testing experiment was to place beyond doubt the preponderant weight of the right cerebral hemisphere. No comprehensive inductions can be based on a single case, but its confirmatory value is unmistakable at this stage of the inquiry; and thus far it sustains the conclusions previously arrived at, and justifies the assignment of the source of left-handedness to an exceptional development of the right hemisphere of the brain; with results of a greatly more comprehensive character, apparently affecting the whole functions ordinarily located in the opposite cerebral hemisphere.