No animal has evolved with more than five digits since the terrestrial vertebrates (reptiles, birds and mammals) branched off on their own evolutionary path at the beginning of the carboniferous period 360 million years ago. But why do we have as many as five? As we have seen before, nature tends to furnish us with as many of the parts as we need, and where these are replicated, as with eyes and ears, it is for a good reason. So what do the five fingers do – either individually or together in various combinations – that gives them all a role?
In counting, each finger is exactly equivalent. But for most other tasks, they are as varied as the tools on a Swiss Army knife. The index finger is the best pointer because of its length and the dedicated muscle that straightens it. It is also more manoeuvrable than the other fingers. The index finger belonging to Inspector Bucket in Dickens’s Bleak House is so versatile that it is almost a character in its own right, a confidant for Bucket as he puts it to his lips, to his ears, and rubs it over his nose before wagging it before a guilty man. ‘The Augurs of the Detective Temple invariably predict that when Mr Bucket and that finger are in much conference, a terrible avenger will be heard of before long.’
The middle finger, though a little longer than the index, is a poor pointer: try it and you’ll find that it is hard to straighten this finger while holding the others out of the way. But it has other uses. The Romans called it the digitus impudicus, the finger of impudence – perhaps they took over the custom of giving people ‘the finger’ from the Greeks. It is also called the digitus medicus because Roman physicians were apparently in the habit of using it to stir medicines. Next comes the digitus annularis, which we still call the ring finger, ‘annulus’ being the Latin for a little ring. It has this function for symbolic reasons rather than because it is especially adapted to the task. The ancients believed (incorrectly) that this finger was directly linked to the heart by a special vein. The little finger is called auricularis, because even it is not useless: it is just the right size for cleaning out the auricle of the ear.
Finally, there is the thumb, ‘the father of technology’, according to Raymond Tallis. It is our having an opposable thumb – meaning to say we can employ it in opposition to the other fingers – that greatly increases the capability of the hand, so that it is able to exert a wide variety of grips. Montaigne, in his note ‘On thumbs’ in the Essays, gives a correct derivation for the French for thumb, pouce, from the Latin pollere, meaning to excel in strength. He also offers a spurious but nonetheless apt alternative name, anticheir (derived from the Greek, it would mean ‘opposed to the hand’); both terms are revealing about the unique importance of this digit.
But it is the opposed thumb together with the mutually independent operation of the fingers that really gives us our dexterity. The names of individual fingers hint at dedicated uses for each of them, but there is so much more they can do in their many permutations, from the way the forefinger and thumb delicately pinch in order to pick a flower or remove a contact lens, to the carefully balanced use of all five to wield a pair of chopsticks. Add to this the dizzying speed of other manipulations – of cards by a trickster, of strings by a guitarist – which earns its own special name of prestidigitation.
Palms have been ‘read’ for millennia, but the practice has only recently been put to the scientific test. The tradition was perhaps made respectable by Aristotle when he observed carelessly in his Historia Animalium that the life line across the hand seemed to be longer in long-lived persons. Why should it be the hand that reveals our fate? It seems simply that the palm of the hand contains a suitable number of legible features and is easily offered for inspection. In 1990, scientists at the Bristol Royal Infirmary looked at the life-line length of 100 consecutive autopsies. Surprisingly, perhaps, they did find a correlation between the length of the life line and the age of death. But it was not quite the evidence for the veracity of palm-reading that it might seem. As the scientists point out: ‘With increasing age we all become more wrinkly.’ In their paper, they admit that a better idea would be to monitor the life-line length of a number of subjects over a lifetime, preferably, they add tongue-in-cheek, ‘with investigators meeting every 10 years in exotic locations to report preliminary results’. Such a study has yet to be undertaken.
Another obvious feature of the hand is the length of the fingers in relation to one another. They were once thought to denote five (not Shakespeare’s seven) ages of man, from the little finger of youth to the ring finger at the time of marriage to the longer fingers of maturity and finally to the decline of the thumb. In 1875, a German anatomist and anthropologist named Alexander Ecker observed that women’s index fingers tend to be longer than their ring fingers, while men’s are the other way round. This was such a curious finding that others rushed to confirm it – which they did, but when nobody could work out what it actually meant, the information was quietly ignored. This was the case until 1983, when Glenn Wilson at the Institute of Psychiatry in London responded to an invitation from the Daily Express to contribute to a survey of ‘changing attitudes of women in the 1980s’. His questionnaire to female readers asked about their assertiveness and competitive instincts, and requested, by the by, that they measure the lengths of their fingers. The results showed some tendency for women with a low index to ring finger ratio to be more assertive, in other words the women with more male-like fingers behaved more like men (it having been taken as read, it seems, that assertiveness is essentially a male attribute). This discovery confirmed finger ratio as a convenient indicator of the level of testosterone to which a person has been exposed in the womb. Research based on finger ratios has mushroomed, and they have now been used in studies of sexual selection, sexual orientation, fertility, spatial reasoning, sporting ability, musical talent, autism (which occurs primarily in males), and success in financial trading. In 2010, investigators at the University of Warwick obtained results to suggest that men with long index fingers are less likely to get prostate cancer. It seems the hands have much to tell us yet.
The most pervasive and most divisive conclusion we have drawn from our hands is that one is better than the other. Preferment of the right hand develops very early in life. There is evidence that at fifteen weeks’ gestation most of us exhibit a preference for sucking our right thumb. Tracking a number of subjects before and following birth, Peter Hepper at Queen’s University Belfast found that the prenatal right-handers all kept their right-handedness as children. Most of the left-handers retained their preference for the left, but some switched to the right.
It clearly disturbs us on some deep level that we possess these two sets of limbs that appear to be entirely symmetric and yet are generally asymmetric in use. This imbalance is one of the oldest bases for discrimination: between left and right. The Bible repeatedly declares a bias in favour of God’s (and everybody else’s) right hand and against the left. Arbitrarily, it seems, in the gospel according to Matthew, God demands that those ‘on the left hand, Depart from me, ye cursed, into everlasting fire’, while those on his right ‘inherit the kingdom’. A wide vocabulary exists to label or insult left-handers, and in many languages the very terms ‘left’ and ‘right’ are loaded with bias. From other European languages, and sometimes quite ancient roots, English alone has acquired the terms gauche, sinister and cack-handed, the last being a reference to the custom in predominantly right-handed societies of reserving the left for wiping away faeces or ‘caca’. I even have a book on symmetry that contains this entry in the index: ‘laevo-, see under: dextro-’. The political left, incidentally, which may or may not have this pejorative connotation according to your own political views, originates in the layout of the French Assembly, where, after 1789, the revolutionaries sat on the left wing.
Left-handers are in a minority, but the true size of the minority is uncertain. In 1942, the psychologist Charlotte Wolff could write without pausing for reflection that ‘in these days not more than 2 to 3 per cent of the population are left-handers’. Recen
t studies suggest, by contrast, that up to a third of children would develop as natural left-handers in the absence of external influences. This matches the apportionment of left- and right-handedness in Palaeolithic man inferred from the way they shaped their axes. But in many environments, there is strong social pressure to be right-handed – even left-handers must shake hands with their right, for example – so the observed proportion of left-handers is often much less than this. United States army recruits, for example, report only 8 per cent of left-handers in their ranks.
The systematic elimination of left-handedness is not what it used to be, though. Listening one day to the statistical curiosities that are the staple fare during boring moments of test match commentary, I was surprised to learn that the first time in cricketing history that the first four men put in to bat were all left-handers was in 2000 – since when it has happened twenty-eight times. On the face of it, this is most odd, given that the statistical record goes back to 1877. It could be down to a chance occurrence of gifted left-handed batsmen, but it’s far more likely to be a reflection of the fact that we are now less apt to penalize left-handers in all walks of life. In many sports, of course, being left-handed can give an advantage because all players, even other left-handers, are more accustomed to playing against right-handers.
More insidious pressures remain, however. Almost every one-handed activity, from zipping trousers to using a cash machine, has a cultural bias in favour of right-handers. A visit to Anything Left-Handed, the shop of the Left-Handers Club, which once occupied premises in London’s Soho but now trades online, hints at the extent of the iniquity. There are scissors, tin openers, fountain pens and much else in the tiny shop and in its reverse-paginated catalogue. There are also products where many people would never suspect a bias – rulers and tape measures (numbered from right to left), corkscrews (turning anti-clockwise for a better purchase), kitchen knives (serrated on the other side of the blade). The shop also stocks CDs of music played by left-handers, although I’m not sure how you are supposed to hear the difference. But I’m disappointed to find it does not have Ravel’s dazzling Piano Concerto for the Left Hand. The work was written for Paul Wittgenstein, the brother of the philosopher Ludwig, who lost his right arm in the First World War. When Ravel had finished the work, Wittgenstein proclaimed it too difficult and demanded changes. ‘I am an old hand at the piano,’ he joked. ‘And I am an old hand at orchestration,’ Ravel snapped back. Other left-handed pianists hanker for a reversed keyboard with the deep notes on the right allowing the left to carry the melody for once. While we are at the keyboard, we might note that the size of the hands can also affect the kind of music that gets written. Rachmaninov had hands that could span an octave and a half, which puts some of his compositions literally beyond the reach of many daintier players.
The discrimination designed into so many everyday objects may be rather more than an inconvenience. In 1989, the psychologist Stanley Coren surveyed a large number of students at the University of British Columbia and found that a left-hander was almost twice as likely as a right-hander to have a car accident, and half again as likely to have an accident while using a tool of some kind. Coren attributed the cause not to innate clumsiness of southpaws, but to design that is consciously or unconsciously biased to suit right-handers. He estimated that left-handers’ life expectancy was reduced by eight months in this way.
The hands are not our only handed body parts. Inside the human trunk, asymmetry is the norm. The heart is on the left and the liver is on the right. The stomach lies to the left. The left lung has two lobes, the right has three. There are little-noticed external differences, too. Our hair falls to one side or another. The left breast is usually a little larger than the right. The left testicle usually hangs lower than the right, even though the right one is generally heavier. The reasons for this aren’t firmly established, but it has been known for a long time: the majority of Classical statues confirm it.
In a way, it is the presence of symmetry in the body at all that is more remarkable than when it breaks down. The process of embryonic development is one of progressive loss of symmetry. The fertilized egg is spherically symmetric, but with each cell division it loses some symmetry. As organisms that must live under the influence of gravity, we quickly lose any top–bottom symmetry. With locomotion necessarily comes the need to move forward, and so a sense of front and back, which causes us to lose symmetry in this direction. That leaves only the symmetry in the third dimension, from side to side. Here there is no distorting environmental influence, and so the symmetry seen in the embryo can persist. Yet occasionally, this tidy bilateralism is subverted, and something grows on one side but not on the other. To see why this is, we must look more closely at what happens in the developing embryo.
The process of symmetry loss gains pace with the emergence in the embryo of an arrangement of cells known as the primitive streak. As growth continues, cells begin to apportion themselves equally either side of this putative midline of the organism. Although the same set of genetic instructions is used to make the corresponding parts on either side of this line, it is something of a mystery as to how the cells, which seem otherwise identical, direct themselves into mirror-image positions. The cells may pick up positional information by detecting variations in waves of cellular activity, rather like a driver using a satellite navigation system. But this still leaves the problem of directed left–right asymmetry.
An unignorable potential clue to the phenomenon was revealed in 1848, when the young Louis Pasteur discovered that certain chemical molecules exist in left- and right-handed versions. He knew that tartaric acid rotated polarized light (light filtered in a special way) to the right, while tartaric acid made synthetically had no such effect. When he crystallized some of the synthetically made acid, he found he had an equal mixture of crystals that were mirror images of one another. Half were the ‘dextrorotatory’ form, the one that occurs in nature, and half a new ‘laevorotatory’ form. It was eventually discovered that many biological molecules, including sugars, amino acids and DNA, have this property. It can matter greatly which form of these substances is present in our bodies, as the author Lewis Carroll seems to have guessed. Lactose and lactic acid are two examples of so-called ‘handed’ molecules that occur naturally in only one of their handed versions. In Through the Looking-glass, Alice holds her kitten up to the mirror and wonders if it would like it there, but then she considers: ‘Perhaps Looking-glass milk isn’t good to drink.’
It is hard to believe that this molecular handedness is not connected in some way with the overall handedness of biological organisms. So are our left–right asymmetries ‘due to some molecular asymmetry that is transferred to a global asymmetry’, as the embryologist Lewis Wolpert suggests? If so, how might this scaling-up take place? Wolpert speculates that asymmetric molecules produced along the embryo midline may function chemically to push certain other molecules – and cells – preferentially to one side rather than the other.
A chemical mechanism like this may explain the left- and right-hand biases we (almost) all share, such as having the heart on the left. But what makes nature produce handed molecules in unequal quantities? The answer to this is not known for sure. However, the mirror-image forms of amino acids and other biologically important substances contain one last asymmetry – more of their electrons spin leftwards than rightwards. Might this explain the bias? If so, how did this disparity arise? Perhaps there was some cosmic event to cause it, such as a great burst of polarized light. In that case, there may be another half of the universe where the opposite bias applies.
As for left- and right-handedness in behaviour, the psychologist Chris McManus proposes a genetic mechanism. Handedness may be controlled by two genes, not a left gene and right gene as you might expect, but one that favours right-handedness, called dextral, and one that does not discriminate, called chance. Such a mechanism would account for the observed (natural, rather than culturally suppressed) minority of left
-handers in the overall population. As is always the case when the talk turns to ‘a gene for . . .’, it raises the prospect of genetic therapy. We might one day be able to ‘cure’ left-handedness by suppressing the chance gene. But would it not be a sign of our liberation from age-old superstition if instead we chose to suppress the dextral gene and leave everything to fifty-fifty chance?
The Sex
The best sight gag in the entire history of art must be the fig leaf. How large it is! And how very suggestive in its shape! How it engrosses what it purports to hide. How many other plant leaves might have done the job with less blatancy. And yet the fig leaf it assuredly is that artists have elected to use when asked to preserve the public decency. The Bible gives them their cover story: in Genesis, when Adam and Eve realized their nakedness, ‘they sewed fig leaves together, and made themselves aprons’. But aprons are garments that surely provide rather more coverage than the single, strategically positioned leaf of artistic convention, with its three major lobes simultaneously screening and outlining the penis and testicles behind, and two further vestigial lobes appearing so neatly to represent curls of pubic hair.
The artistic fig leaf became all but mandatory when in 1563 the Roman Catholic Council of Trent ruled that ‘all lasciviousness be avoided’ in religious images ‘in such wise that figures shall not be painted or adorned with a beauty exciting to lust’. Up until that date, in Classical statues and in the Renaissance art inspired by them, false modesty had taken a different form. The human figure was often modelled on the bodies of athletes, who performed their exertions naked. In a monument to a civic dignitary, a philosopher or a general, a well-toned body was the sculptor’s means of indicating their good citizenship. The artist would carve the genitals on such statues to be somewhat less than life size. Unless the point was to celebrate fertility, as with the conspicuously erect penis of Priapus, the Greek god so eagerly adopted by the Romans, a sculpted penis of normal size, even a flaccid one, was thought vulgar and a distraction from the achievements that it was the business of the statue to celebrate.
Anatomies: A Cultural History of the Human Body Page 23
