Anne Harrington’s masterly account of homo duplex is more than just an account of the emergence of our understanding of our own inner dissymmetry. It sets the striving towards comprehension amid the social prejudices and pressures of the 19th century and shows how the expectations of the time moulded scientific opinion. We are made aware of the traffic of ideas about this most intimate of parts between those who were discovering and those who were using the discoveries. Here we see science in the grip of society.
This study in conceptual history deals with the latter half of the 19th century, when the paradigm of the physical sciences had fired the imagination of those who sought to understand. It begins, though, further back, with the well-meaning dabblings of Descartes which have so wasted the time of those with the serious intention of getting to know the pregnant matter that clogs the space between our ears. Descartes had little difficulty in locating the seat of the soul. Having adopted the skull as its vessel, he needed to find a centre of unification amid what seemed to be a confusion of duplicated detectors: two eyes to see with, two ears to hear with and two hands to feel with. What better than the pineal gland – the only anatomical feature, he thought, not duplicated inside the head. Moreover, how satisfying that the gland was – as he thought, incorrectly – unique to us cosmic supremes.
Unfortunately for the soul, swashbuckling adventurers were to go in search of it as vigorously as they stormed Africa and the Indies. There was a certain relief that the soul was not garaged in the pineal gland, which seemed far too simple a setting for so kingly an entity, and the search for the sensorium commune was to remain one of the chief themes of 18th-century neurology. It was particularly upsetting to those who favoured religious obfuscation above true knowledge that Franz Gall should have the temerity to set about mapping the convolutions of the cerebral hemispheres and ascribing individual functions to them. For their audacity in presuming to map, but not for their success, he and his followers were declared guilty of undermining the unity of the soul, human immortality, free will, and the very existence of God. How much more satisfying it was to think of the brain as an engagingly sculpted single organ elaborately contoured, according to the inscrutable creator’s whim, as a habitation for the soul. It was presumed that the brain and hence the soul could be sliced away, and as its bulk dwindled so we would regress through inferior types, roughly in the order of women, apes, rabbits and cock-roaches, our capacity for intellectual activity gradually fading until it vanished altogether. There was even some sparse experimental evidence for this view, for what work there was on brains was largely the result of hacking through them, with little notice taken of their structural variation.
The classical equation of symmetry and perfection, however, remained with Gall despite his preoccupation with cranial bumps. He taught that the mental faculties existed in perfectly symmetrical duplicate. And here we have the problem of homo duplex. For why should he, despite his evident superiority amid the general detritus of creation, need what looked suspiciously like two identical brains stuffed into the same skull? For Gall, one of the hemispheres was a spare wheel in case the other fell on hard times, atrophied from under-use in stupid people, or expired in the brilliant from over-exertion. It was there to take up the slack when the other was feeling under the weather or was simply worn out. One hemisphere, some thought, could act as a kind of cerebral chaperone, overseeing the malevolent acts that might be favoured by its twin.
The trouble was – and here is where the neuro-sciences really begin – that it slowly became apparent that unilateral damage led to malfunction, so that the spare tyre idea was not very fruitful. Arthur Wigan had been attracted to considerations about the duality of the brain when he had attended an autopsy and observed, much to his disquiet, that when a particular skull had been opened, the brain of an apparently perfectly normal individual had one hemisphere altogether absent. That case was not alone: several others come to be publicised in which yawning chasms or substances resembling cold porridge or fried egg were found where the rest of us, we presume, have brain. Was a single hemisphere therefore sufficient?
There was also great uncertainty surrounding the function of the corpus callosum, which ties our hemispheres together. Wigan dismissed it as an organ of little importance, more an engineering solution to the union of the hemispheres, a strap, than anything to do with consciousness. Some thought that it provided a unity of consciousness in the two brains, but it was puzzling that damage to the corpus callosum seemed to have no discernible effect on the functioning of brains. For those who pictured the hemispheres as in dependent brains, the unity of consciousness was explained by drawing the analogy with a pair of identical twins who had lived cooped up together within the cranium, so that it was hardly surprising that they continued to feel a unified personality.
The major advance came when interest in the brain migrated from the Austria of Gall to France – for some the only proper receptacle of knowledge about this noble organ. Thus we come to 1860, and to Paul Broca, who in these pages emerges as a faintly flawed giant on the track of hemispheric differentiation. Initially, though, it is a differentiation between front and back, rather than left and right. Broca, a Huguenot, was predisposed to localisation of function since that harmonised with his political disposition: he saw that demonstrating the delocalisation of the soul was a first step to dispersing the power of the religious orders. In 19th-century France the division was clear: those who were in favour of cerebral localisation, and hence were against the unity of the soul, were in favour of regicide, were adversaries of the death penalty and despisers of Papal infallibility – in a word, atheists. The anti-localisers, sweet brethren, were legitimists and upholders of whatever had conditioned them. A similar alignment was to recur later in the 19th century when neurologists had to interest themselves in hypnosis, somnambulism and double personality because the lay public tended to sympathise with spiritualistic or supernatural interpretations. As keepers of the faith in the rationalistic world view, they had to quell these interpretations. The resurgence of interest in the brain in the late 19th century can be traced to the effort to fight the creeping tide of the occult.
Initially, Broca considered only frontal localisation of language, which also seemed to fit the general swelling of heads in what were then regarded as the more advanced nations. Even he was initially reluctant to consider its asymmetrical localisation in the left hemisphere alone. This was noticed first in 1863 by an obscure country doctor, Marc Dax, whose work had been brought to the attention of the Académie de Médecine by his son. That same year, Broca began to struggle with the problem of hemispherical asymmetry. It is not clear if he knew of Dax’s work, and he denied that he did. The prospect of hemispheric asymmetry was all terribly worrying. Functional lopsidedness would force the conclusion that nature had created two apparently identical organs which functioned differently, or one of which failed to function at all. It would raise the spectre of the brain as an organ that was beyond rational scientific exposition, so opening the door to religious obscurantism. It was remembered, however, that some people were left-handed, so that it was perhaps not outlandish that speech, too, was left-hemisphered.
Then, suddenly, it was no more absurd that the brain should have a certain amount of functional autonomy than that the body should have a certain amount of freedom of motion on its two sides. Broca’s opinion, based on the Lamarckian tradition of the time, was that the two hemispheres had the same potential for growth, but that over the generations the left was more precocious and hence was educated into dominance. But he was troubled by the healthy look of the third frontal convolution of the right-hand hemisphere: surely spare parts of the brain would atrophy with lack of exercise? That notwithstanding, Broca was able, in the light of the new dawn, to extend a clinical observation into a view of human dominance: ‘Man is, of all the animals, the one whose brain in the normal state is the most asymmetrical.’ Only in the supreme animal, man, could asymmetry be educated-in so substantially. Moreover, not all races were equally asymmetrical. European man, and presumably the French in particular, was a paragon of asymmetry. Broca was even able to assure himself that asymmetry was greater in the brains of whites than in those of negroes. The Australian was known to resist all attempts at improvement and was therefore plainly inferior to the rabbit, which, once trapped in a snare, can be domesticated. Women were quite obviously more symmetrical than men, and animals are notably even-headed.
The brain thus became a mirror of 19th-century society. The prejudices of the century led to a flamboyant eruption of quackery and shaped the interpretation of haphazard clinical observation and tests. The idea that the two hemispheres could be discussed in sexual terms arose from current views on the biological status of women. Gustav le Bon, for instance, took the view that the brains of many Parisian women more closely resembled those of gorillas than those of adult white men. Yes, of course, a few intelligent women were cited here and there, but such women were so thin on the ground that they could safely be dismissed as freaks. Not only were women internally more symmetrical than men, they were also dominated by their occipital lobes (presumed to be the centre of emotion and instinct – the inhuman dark side of nature). This was regarded as plain common sense: the bulk of a woman’s body is so taken up by the equipment needed for reproduction that it was thought hardly surprising that the related regions of their brains should be heavily developed too. Gaëtan Delaunay traced inner asymmetry outwards into motor asymmetry. Superior races, he noted, tend to gravitate to the right when walking (and, presumably, driving). All French national dances rotate to the right. The middling inferior races – Chinese, Turks, Mexicans – turned to the left. Negroes simply jumped up and down.
Harrington’s exposition deals mainly with the abnormal – those with eggs where others have heads, those whose hemispheres were awry, those who shifted between personalities, such as Louis Vivé, a young man with a turbulent childhood who became a modest and engaging young gentleman when strapped to a magnet. Jon Elster’s wide-ranging series of essays, now issued in paperback, deals with normal man. The Multiple Self considers the question of whether the normal self is a unity, or whether it should be regarded, in some non-metaphorical sense, as divided. Just as deep oil wells were discovered by the smear of oil that found its way to the surface, so, perhaps, can the existence of multiple personality be detected in the phenomena of self-deception, preference, an individual’s conflicting beliefs or weakness of will. Once one starts to speculate in this way, why stop with twin brains: why not admit the possibility that we are not merely double but multiple? The possibility is explored that we may tune into different selves much as we tune into a radio station.
What seems to be a much less problematic aspect of our functioning is brought into focus by Mary Warnock in her book on memory. Her aim is to find an answer to the elusive question of why we value so highly our ability to recall the past. Her answer, such as it is, centres on the relationship between the concepts of memory and personal identity as seen by poets, philosophers, novelists and other writers. With such a whimsical sample she cannot be expected to come to very sharp answers.
Some of the insights of each of these practitioners reveal engaging examples of what we can recall and how it is deployed in art. Yet this is a kind of literary butterfly-collecting, not science. She arrives at the unsurprising conclusion that the importance of memory lies in its importance to the sense of one’s own continuity through time. On the journey to this climax we are told that the observation that memory seems to belong to animals makes us less certain that it is a purely ‘mental’ phenomenon. We are also informed, in a patch of wishful thinking, that the computer analogy does not explain the difference between the memory that may work efficiently but of which we are not aware, and conscious memory, where we know that what we are doing is remembering. The lack of incisiveness could have been avoided by accommodating the scientific knowledge of the past hundred years and the attitudes – some would say prejudices – which have been inspired by progress in computer science, artificial intelligence and the neuro-sciences. As it is, what we get is Wordsworth instead of Turing.