The Puzzle of Left-Handedness (27 page)

The shift to the right is simply a representation on a graph of the well-known lopsided distribution of left- and right-handers, and Annett believes it’s caused by what she calls a right shift factor, the product of a gene that does not occur in everyone. Those who have it are guaranteed to be right-handed. If you don’t have it, then it’s a matter of chance and of circumstances whether you’ll be left-handed, right-handed or neither, and to what degree.

To make the picture clearer we might want to regard the right shift factor as a gene with two variants. One of them, let’s call it r, causes right-handedness, while the other, which we’ll call
NIL
, does nothing at all.
NIL
behaves recessively, Annett says, so everyone with an
R-R
combination is right-handed, as is everyone with an
R-NIL
combination. Only individuals with
NIL-NIL
may perhaps by left-handed, depending on other conditions. If those conditions are entirely neutral, then again we would expect a chance distribution: one quarter of
NIL-NIL
people are left-handed, half have no hand preference and the rest are right-handed.

The distribution of left-handedness, right-handedness and mixed-handedness in animals (broken line) and humans, according to Marian Annett.

This provided Annett with a neat explanation not only for the uneven distribution of hand preference but for the fact that left-handers have a greater likelihood than right-handers of producing left-handed children. So far so good.

There is a further piece of evidence that supports her idea, arising from
situs inversus
, that rare reversal of the inner organs. It’s a disorder that seems to be caused in exactly the way Annett describes. Research, some of it carried out on split salamander eggs, shows that
situs inversus
does not result from a genetic defect, as had been assumed, but from the absence of any instruction as to which way round the organs should be constructed. Roughly half of those salamander individuals that lack the instruction go on to develop normally, the rest have their inner organs reversed. So mechanisms of the type Annett describes do in fact exist.

Yet Annett gets nowhere when it comes to twins. Her theory doesn’t help to explain the elevated number of left-handers among both monozygotic and dizygotic twins. For the former you might want to attempt to solve the problem by assuming that they include far more
NIL-NIL
individuals than the rest of the population, but this is a blind alley. After all, the brothers and sisters of twins have the same parents, so they too should have an elevated chance of a
NIL-NIL
combination, giving them as great a likelihood of being left-handed as the twins themselves. Almost all studies show this is not the case. And elevated rates in dizygotic twins remain a total mystery.

It seemed at this point as if every attempt to explain left-handedness as a product of genes was doomed to run into the sand. Moreover, a separate story was needed to explain cases in which left-handedness is accompanied by all kinds of ailments that point to brain damage. Many people were beginning to suspect that left-handedness might in all cases be the result of accident or injury.

30

Hormonal Left-handedness

Although we now know for certain that the Roswell incident of 1947 was a fairytale, in 1974, on a top secret military training ground in the American state of Nevada, a
UFO
really was shot down by the
US
Air Force and held at a secret location. One of its occupants lived for some weeks and was interrogated at length by America’s most secret agents. Wherever secrets are held they will leak out and so it comes about that we know the
UFO
came from Mars, and that it was not on its first mission. We also know how profoundly Martians differ from us. They reproduce without sex, a process from which they emerge as adults. They do not have gender, they do not understand the concept ‘child’, and they are unwavering rationalists – which is how they came to master interplanetary travel so soon, while human beings were still making their first paltry efforts at it.

The surviving Martian, consistently referred to in the secret interrogation reports as Alien 47 – an irresistibly evocative fact to conspiracy theorists – said that this was their first mission to earth and that their surface transporter had been shot out of the sky right at the end of their mission. They had just put back on earth the last abducted human to have been studied onboard the mother ship, which had been lurking all that time unnoticed on the dark side of the moon. Over the course of a three-month stay close to the earth, they kidnapped fifty to sixty people and laid them on their examination table, hoping to solve a puzzle that had held the Red Planet in its grip ever since the autumn of 1971 (earth years)
.

On 27 November that year Mars was struck for the first time by an object originating from earth. It was the Russian Mars 2 orbiter and lander, which was sadly dashed to pieces. The Martians managed to save only a small Russian flag from the wreckage, on a stand of chrome-plated steel wire – the interrogators had to rack their brains for a long time before they worked out this was what Alien 47 was trying to describe, since the Martian had no earthly idea what flags were. Five earth days later the Mars 3 flew into the planet’s thin atmosphere and made a successful landing. The shocked Martians lost no time in getting hold of the contraption and rendering it harmless, which is why the Russians lost radio contact almost immediately. This time they recovered from the craft a plaque with what the Martians saw as rather primitive mathematical symbols. But there was also something that intrigued them immensely. It was a pile of passport photos that a Russian technician had slipped into the spaceship to give aliens an idea of what human beings looked like.

It seemed from the photographs that there were two kinds of earthling, a very common sort with a smooth chin and a rare kind with what could be described as shrubbery around the mouth. The Martians, who were all as alike as peas in a pod, had never seen anything of the sort before. They decided to mount a mission to the earth to find out what bizarre life form they were dealing with. This was the mission at the end of which Alien 47 fell into earthmen’s hands.

During the Martians’ study of the abducted and anaesthetized humans, it turned out that on some smooth chins there were fresh little cuts, as well as red spots on the adam’s apple. No matter how carefully they searched, those cuts were never found hidden in amongst chin-shrubbery. Alien 47 said proudly that the specialists on board, after puzzling long and hard, worked out that all the smooth chins must have been created by an endlessly repeated ritual lopping process. Clearly that daily trauma did not usually affect people so much that visible marks were left, but in some cases it did. Therefore, they concluded with relief, there was only one kind of human after all, just as there was only one kind of Martian.

The interrogation transcripts, typed out verbatim, show in vivid detail how the astonished interrogators, sometimes unable to suppress a chuckle or two, tried to disabuse Alien 47 by telling him the human population was made up of men and women. And that there was something called childhood. And that children never had beards and therefore, like women, didn’t need to shave. Which was why there were so many perfectly smooth chins. But Alien 47 went on stubbornly shaking his head. That couldn’t be true, he insisted. Femaleness, childhood, a theory involving such bizarre notions made no sense to him, especially when there was a far simpler and perfectly adequate explanation. They must think he was stupid, he reproached the agents. Imagine, he said mockingly, if he were to come home with such an unconvincing story. As soon as the governors of Mars had stopped laughing they would deport the whole crew to the feared mines of Baf! Then, exhausted, Alien 47 fell into some kind of coma from which he never awoke. What eventually became of him, nobody knows.

Of course Alien 47 was wrong, but he did exactly what every sensible scientist is supposed to do: he looked for the simplest possible explanation for the phenomena he observed. After all, the fewer assumptions you rely upon, the fewer flawed assumptions you can make. So the stubborn fact that some cases of left-handedness are attributable to brain damage caused quite a few people to believe that all left-handedness might have its origins in trauma. In other words, people concluded that left-handedness is generally a result of damage to the brain, which affects control of the true preferred hand to such a degree that the other hand functions slightly better, yet is not so severe that any other effects can be readily observed.

Even though many of the studies linking left-handedness to some kind of disorder are of dubious quality, there are so many of them that we have to acknowledge that left-handedness can sometimes be a result of disturbed development in the womb or of brain damage caused before, during or shortly after birth. Aside from associations with all kinds of ailments and disabilities, connections have also been found between the occurrence of left-handedness and long or difficult labour, caesarean section, a relatively high age of the mother, incompatibility of the rhesus factor and other comparable risk elevators. Less than satisfying though it may be, we are forced to conclude that almost everything that can possibly go wrong while a fertilized egg develops into a newborn child may have left-handedness as its main result, or as a side effect.

This does indeed make it extremely tempting to see pathological left-handedness, the result of physical trauma, as the only kind there is. It’s tempting in both its simplicity – it leaves us with a single cause, whereas all other theories inevitably start off with at least two forms of left-handedness – and in its concreteness and plausibility. There’s nothing strange or difficult about the idea of damage to a specific bit of brain tissue, and of course damage does sometimes occur in the womb or during labour and its aftermath.

Another advantage of a general theory of trauma is that it makes the raised percentages of left-handedness in twins easy to explain. The two foetuses are crammed tightly together, which in itself involves certain risks, and one of the two always has to wait longer during childbirth. This entails an increased risk of oxygen deprivation and, who knows, damage that causes left-handedness.

It sounds convincing, yet the foundations on which this kind of reasoning is based are far from sound. First of all, trauma theories depend on the unspoken and unproven assumption that we are all right-handed by nature. This of course cannot be taken for granted, so proponents of this theory, like their rivals, have to explain two phenomena. Which will not be easy, since research on animals shows they have no general preference for either the right or the left.

Second, the simple fact that 10 per cent of the population is left-handed would mean that at least 10 per cent of people start life with an injured brain. In fact the implications are far worse still. In all groups in which left-handers are over represented, the overwhelming majority are nevertheless right-handed. The number of people going through life with brain defects must therefore be huge if this theory is correct, since if the left-handedness of someone who suffers from a particular disorder points to a problem with their brain, why would that not also be the case with at least some of the right-handers in the same group?

Conversely, left-handers are vastly more common than the ailments with which they are associated. Alien 47 saw many more unblemished smooth chins than cut and scraped ones, and he wrongly attempted to explain this based on a single cause: shaving. That’s precisely what’s happening here. The trauma theory means that practically every knock an unborn child receives leads immediately to left-handedness and only occasionally to other abnormalities. This seems extremely improbable.

Nor should we forget that far from all associations between left-handedness and a disorder of some kind necessarily point to trauma. A trauma is something that does not occur naturally in an organism but is suffered at some point during the course of its life because of external influences, or as the result of some kind of defect. Take for example the Dutch research carried out in 2005–9 that discovered a connection between breast cancer in young people – which is fortunately quite rare – and left-handedness. If there is indeed a connection, this would point towards a non-traumatic factor that by pure chance increases the odds both of left-handedness and of susceptibility to early breast cancer. It might well be a variant of a gene, but it could also have something to do with the regulation of hormones.

The existence of pathological left-handedness is a far less compelling motive to look to trauma for an explanation than it appears to be at first sight, because in the absence of a good reason for thinking that we are all right-handed by nature, pathological right-handedness must exist as well. The thing is, we just fail to notice it.

The invisibility of pathological right-handedness is a direct consequence of the uneven distribution of left- and right-handedness and the fifty-fifty chance of a trauma occurring on either side of the brain. Try the following simple calculation.

We start with 10,000 children, of whom 10 per cent are naturally left-handed. For simplicity’s sake we’ll assume that brain traumas that cause a reversal of hand preference occur in one child in every hundred. Then the following happens:

• In the course of their development 50 children will suffer damage to the left side of their brains and 50 to the right.
  
• Of those with damage to the left brain, the natural right-handers become left-handed as a result. There are 45 of them. No change in hand preference occurs in the other five, the natural left-handers.
  
• Of those with damage to the right brain, the natural left-handers become right-handed as a result. There are five of them. No change in hand preference occurs in the other 45, the natural right-handers.
  
• At the end of the process the number of left-handers is 1,000 – 5 + 45 = 1,040, including 45 pathological left-handers. This means that almost 1 in 20 left-handers is a traumatic left-hander.
  
• At the end of the process the number of right-handers is 9,000 - 45 + 5 = 8,860, including five pathological right-handers. So only 1 in roughly 2,000 right-handers is a pathological right-hander.
  

The influence of trauma on the size and composition of the group of left-handed children is significant, but the tiny handful of pathological right-handers is lost in the ocean of right-handedness of which it is part. If the group of left-handers increases by 4 per cent, the proportion of left-handers in the population as a whole increases by around half of 1 per cent. This fits nicely with the experience that in groups with some kind of disorder the number of left-handers is often slightly larger than normal. But even to explain such a small increase we have to assume that in one in a hundred children a trauma has occurred that affects the preferred hand just enough to make the other hand do its work instead, while at the same time producing effects so slight that no one notices anything wrong. After all, everyone is under the impression they’re dealing with a normal left-hander.

These are stringent demands to make of traumas, events that have a natural tendency to affect people in random places to a random degree in random ways. If that one specific type of trauma that influences hand preference occurs so often, how improbably high must be the total number of accidents large and small? Or is there a risk factor that often causes this specific type of trauma? One man who has travelled a long way down that particular road is Norman Geschwind.

From 1969 until his death in 1984 at the age of only 58, Norman Geschwind was professor of neurology at the renowned Harvard Medical School. He was one of those strapping men who achieve an almost godlike status in their field, the kind of man who always thinks a little further, a little faster and better, coming up with more original ideas than other people. And he thought: testosterone!

To Geschwind the concept of trauma did not mean that someone who was left-handed would inevitably experience negative consequences. On the contrary, he believed that left-handedness was merely an easily detectable indication that the person in question might to a greater or lesser degree have a brain that was organized differently from the norm. He claimed this anomaly coincided with a number of other noticeable characteristics, bringing with it an increased risk of being a man, of having autoimmune diseases ranging from hay fever to the strangest of allergies, of getting migraine, being born with a hare lip, suffering from epilepsy or presenting with various other aberrations. It might well be that these were offset by a decreased risk of a series of other disorders, much like the way that carriers of sickle cell anaemia are less susceptible to malaria. It sounds bizarre, but it does indeed turn out, for example, that schizophrenics with twin siblings generally have far better mental health when one or other twin is left-handed than when both individuals are right-handed.