The Faber Book of Science (56 page)

The human brain consists of ten to fifteen thousand million nerve cells. (The anatomy books are always more precise, each opting for fourteen or eleven or fifteen billion as if its choice is the true and unassailable figure.) If that kind of number is bewildering, being three times as many as there are human brains alive on this planet, the number of synapses (nerve cell connections) is a thousand times more so, there being about one hundred million million of them, or more than the total number of humans who have ever lived since we acquired this fantastic brain in full measure those thousand centuries ago. Coupled with the nerve cells, supporting and nourishing them, are the glial cells whose number is on a par with the nerve cells that they sustain. By way of comparison, appreciating that such figures can put normal minds in turmoil, the clever little honey bee has about seven thousand nerve cells.

The whole human brain weighs some three pounds in the male and about 10 per cent less in females (or 1,400 grams as against 1,250 grams). This disproportion can seem unfair to women but their brains are relatively bigger, being
2½ per cent of total body weight as against 2 per cent for men. The three pound weight makes our brain among the lightest of our organs, being very much less than muscle (42 per cent of the total weight for males, 36 per cent for females), much less than the combined total for the 206 bones of the human skeleton, less than the twenty-plus square feet of skin, less than the twenty-eight feet of intestine, less than the eleven pounds or so of blood, and just less than the four pounds of liver. However, it weighs more than the heart
(which is one pound), the kidneys (a mere five ounces each), the spleen (six ounces), the pancreas (three ounces), and the lungs (two and a half pounds). A foetus, with its relatively huge head plus brain and its small everything else, is arguably a more accurate representation of
Homo
sapiens,
but that big head wanes proportionately as the child grows wiser. There is undoubted paradox about our most remarkable property, all three pounds of it.

There is also conflict over its abilities. On the one hand, and for many a normal day, a particular brain may exhibit precious little intelligence. Its owner may eat what has been set before him, walk to a bus stop, reach work, perform the same repetitive task, return home, eat again and sleep. An animal could do the same. On the other hand there is the musician Hans von Bülow travelling by train from Hamburg to Berlin, reading Stanford’s
Irish
Symphony,
previously unknown to him, and then conducting it that evening without a score. Some musicians prefer reading a piece of music to hearing the work, claiming that the experience is without the blemishes of an actual performance. Wolfgang Mozart confided that a whole new
composition
would suddenly arise in his mind. At convenient moments he would translate this entire fabric of rhythm, melody, harmony, counterpoint and tone into the written symbols of a score. For those who have trouble with a telephone number or with a name to fit a face, it is even problematical contemplating the gap between us and them, the normal and the genius. Someone once asked A. C. Aitken, professor at Edinburgh University, to make 4 divided by 47 into a decimal. After four seconds he started and gave another digit every three-quarters of a second: ‘point 08510638297872340425531914’. He stopped (after twenty-four seconds), discussed the problem for one minute, and then restarted: ‘191489’ – five-second pause – ‘361702127659574468. Now that’s the repeating point. It starts again with 085. So if that’s forty-six places, I’m right.’ To many of us such a man is from another planet, particularly in his final comment.

The bizarre fact is that the brains of von Bülow, Mozart and Aitken were inherited from a long line of hunter-gatherers. Why on earth, or even how on earth, did a brain system evolve that could remember symphonies or perform advanced mental arithmetic when its
palaeolithic
requirements were assuredly less demanding? And why, as the second major conundrum, did the process stop at least 100,000 years ago? Only since then, via population increase, larger and more settled
communities, division of labour and a subjugation of nature, has the brain of man begun to realize its potential. Yet it is a prehistoric brain, there being no detectable difference (so far as can be judged from fossils) between then and now, theirs and ours, extremely primitive and very modern man.

The solar system is vast, incomprehensible to most of us, and staggering in its distances, and to mention it in the same breath as our three pounds of brain is apparently to relate like with unlike, a thing colossal with a thing minute. But the bracketing together is fairer than might be imagined. The dimensions that astronomers talk about, and seem to understand, have their parallel in the numbers that neuroanatomists relate, almost in passing, as if these too are understood. Already mentioned are the fifteen billion nerve cells, which is also the numeric total (more or less) of stars in our galaxy. Also mentioned are the synapses, a thousandfold greater, and therefore as plentiful as the stars of a thousand galaxies. Astronomers do use such figures, being more aware than most of the thousands of millions of light years existing between us and the furthest parts of the known universe; but there must be a limit even to their
comprehension
.

The human brain, I suspect, can confound them, not in its neurons but in the range of its possibilities. Nerve cells are the basic units, but their synapses create a framework for interconnections, for a variety of ways in which one nerve cell may be linked with another, and for that other to be connected with others yet again. The figure of possible connections within our modern brain is as good as infinite. It is certainly larger than the number of atoms presumed to exist in the entire universe and no one, I warrant, can begin to grapple with that thought. Somehow or other a bipedal, fairly hairless, hunting, scavenging ape did acquire this incredible possession and then handed it on to us. Why it did no one knows, or can even surmise. ‘I haven’t the foggiest notion,’ replied Richard Leakey, anthropologist and skilful finder of early hominids, when asked why or how such a swelling of brain power could have occurred among early, primitive, and scattered tribes of men.

The speed of that swelling was considerable. From about five hundred cubic centimetres – and therefore comparable in size with gorilla
brains – it leaped to the human size of fourteen hundred cubic centimetres in about three million years. Assuming the brain cells of earliest man to be as compressed as in a modern brain this means that some nine billion cells were added during those years, or
approximately
one hundred and fifty thousand per generation. That seems like a big increase for every single leap from parent to offspring, particularly when it is remembered that many invertebrates, all quite astute, have far less than that number, but in size it is not very large. In the brain there are about ten million cells in every cubic centimetre, and therefore that generation gap of one hundred and fifty thousand occupies a sixtieth of one cubic centimetre or just fifteen cubic millimetres. Such an increment is modest if viewed simply as bulk, and many another animal has increased its body size by much more than that per generation, the weight increase being only 0.015 grams or one two-thousandth of an ounce.

If elephants had only achieved their seven-ton weight from their, say, one-ton ancestors at this increment of 0.015 grams a generation it would have taken about four hundred million generations, or roughly eight thousand million years. However, it is tempting to regard
brain-tissue
weight-gain as more problematical in evolution than elephant weight-gain. The brain-gain seems more so because brains are of more significance – at least from our
sapiens
point of view – than mere bulk, a thicker skin or larger trunk. It is easier to be impressed with a tripling of nerve cells in three million years.

The brain growth seems less remarkable if thought of solely in terms of cell division. To achieve 15,000 million nerve cells it is necessary to have just 33 doublings of the parent cell. To achieve half that number only 32 doublings are necessary. In this light the difference between primitive and modern man seems less marked – scarcely more than one extra doubling in three million years. As the adult complement of brain cells is made during the first three months of pregnancy the 33 divisions therefore take place at an average rate of about one every three days. Bacteria double their number every twenty minutes or so, and the foetal brain increase is therefore not particularly rapid. In fact it is equivalent to all sorts of other increases going on in the embryonic human at the same time: liver growth, skin growth and so on. Brain growth just seems more remarkable, particularly when it is brought down to the level of brain cells. To possess 15,000 million neurons at the end of three months’ gestational activity means growing them at
the rate of 2,000 a second. Knowing that many small animals lead quite complex lives with that number of nerve cells, it is arguable that we should be far more intelligent than is actually the case; but it is obviously wrong to compare insect ability, however complex and admirable, with human capability. We are not equivalent to seven million insects. We just happen to have as many brain cells as they possess.

These paragraphs of figures, with so many noughts in them, may confuse rather than enlighten. Their purpose was to show that the acquisition of our three-pound brain is full of contradiction. It was a tremendous increase; yet would have been of little note had it occurred with some other kind of tissue. The three pounds are only beginning to achieve their potential for a very few people in modern times; yet they were developed for all our ancestors in relatively simple times. The brain’s cells and synapses are merely numerous; the quantity of interconnections is about as infinite as anything we know. The brain’s size is plainly crucial; and yet those individuals with twice the brain of others are none the wiser for it. Its growth was undoubtedly critical for the emergence of
Homo
sapiens,
and for the development of this species; yet its size was probably curtailed by the practical demands of a relatively minor portion of anatomy, namely the elasticity at birth of the pelvic canal. It was easy for evolution to permit a steady growing of the foetal head; but birth must have been an increasing problem. Teleologically speaking, it was a good time for the mammals to introduce live birth in place of the egg birth that had ruled, more or less, since life began; but viviparity meant, in time, a limitation to head size. (Even so, we now have a brain more than suited to our needs. Perhaps it will teach us one day how to tap its real potential.)

History is full of examples of apparently simple discoveries that were not made even when they would be surpassingly useful in that culture. Necessity is not necessarily the mother of invention. Men in most of Europe and Asia had adopted the wheel during the Bronze Age. It was used for chariots, as a pulley wheel for raising weights, and as a potter’s wheel for making clay vessels. But in the two Americas it was not known except as a toy in any pre-Columbian civilization. Even in Peru, where immense temples were built with blocks of stone that weighed up to ten tons, these huge weights were excavated, transported, and placed in buildings without any use of wheels.

The invention of the zero is another seemingly simple discovery which was not made even by classic Greek mathematicians or Roman engineers. Only by the use of some symbol for nothingness can the symbol 1 be used so that it can have the value either of 1 or 10 or 100 or 1000. It makes it possible to use a small number of symbols to represent such different values as 129 and 921. Without such inventions figures cannot be added or subtracted by writing them one above another, and multiplication and division are even more difficult. The Romans had to try to divide CCCLVIII by XXIV and the difficulty was immense. It was not the Egyptians or the Greeks or the Romans who first invented the zero, but the Maya Indians of Yucatán. It is known that they had a zero sign and positional values of numbers by the time of the birth of Christ. Quite independently the Hindus made these inventions in India some five to seven centuries later. Only gradually was it adopted in medieval Europe, where it was known as Arabic notation because it was introduced there by the Arabs.

No kind of prediction is more obviously mistaken or more
dramatically
falsified than that which declares that something which is possible in principle (that is, which does not flout some estabished scientific law) will never or can never happen. I shall choose now from my own subject, medical science, a bouquet of negative predictions chosen not so much for their absurdity as for the way in which they illustrate something interesting in the history of science or medicine.

My favourite prediction of this kind was made by J. S. Haldane (the distinguished physiologist father of the geneticist J. B. S. Haldane), who in a book published in 1930 titled
The
Philosophy
of
Biology
declared it to be ‘inconceivable’ that there should exist a chemical compound having exactly the properties since shown to be possessed by deoxyribonucleic acid (DNA). DNA is the giant molecule that encodes the genetic message which passes from one generation to the next – the message that prescribes how development is to proceed. The famous paper in the scientific journal
Nature
in which Francis Crick and James Watson described the structure of DNA and how that structure qualifies it to fulfil its genetic functions was published not so
many years after Haldane’s unlucky prediction. The possibility that such a compound as DNA might exist had been clearly envisaged by the German nature-philosopher Richard Semon in a book
The
Mneme,
a reading of which prompted Haldane to dismiss the whole idea as nonsense.

In the days before the introduction of antisepsis and asepsis, wound infection was so regular and so grave an accompaniment of surgical operations that we can hardly wonder at the declaration of a
well-known
surgeon working in London, Sir John Erichsen (1818–96), that ‘The abdomen is forever shut from the intrusions of the wise and humane surgeon.’ Of course, the coming of aseptic surgery to which I refer below, combined with the improvement of anaesthesia, soon made nonsense of this and opened the door to the great achievements of gastrointestinal surgery in the first decade of our century.

One of the very greatest surgeons of this period was Berkeley George Moynihan of Leeds (1865–1936), a man whose track-record for erroneous predictions puts him in a class entirely by himself.

Around 1900 the famous British periodical, the
Strand
magazine (the first to publish the case records of Sherlock Holmes), thought that at the turn of the century its readers would be interested to know what was in store for them in the century to come; ‘a Harley Street surgeon’ (unmistakably Moynihan) was accordingly invited to tell them what the future of surgery was to be. Evidently not spectacular, for Moynihan opined that surgery had reached its zenith and that no great advances were to be looked for in the future – nothing as dramatic, for example, as the opening of the abdomen, an event regarded with as much awe as the opening of Japan.

Moynihan’s forecast was not the hasty, ill-considered opinion of a busy man: it represented a firmly held conviction. In a Leeds University Medical School magazine in 1930 he wrote: ‘We can surely never hope to see the craft of surgery made much more perfect than it is today. We are at the end of a chapter.’ Moynihan repeated this almost word for word when he delivered Oxford University’s most prestigious lecture, the Romanes Lecture, in 1932. He was a vain and arrogant man, and if these quotations are anything to go by a rather silly one too, but surgery is indebted to him nevertheless, for he introduced the delicacy and fastidiousness of technique that did away for ever with the image of the surgeon as a brusque, over-confident and rough-and-ready sawbones. Moreover Moynihan, along with William Stewart Halsted
of Johns Hopkins (1852–1922), introduced into modern surgery the
aseptic
technique with all the rituals and drills that go with it: the scrupulous scrub-up, the gown, cap and rubber gloves, and the facial mask over the top of which the pretty young theatre nurse gazes with smouldering eyes at the handsome young intern who is planning to wrong her. These innovations may be said to have made possible the hospital soap opera and thus in turn TV itself– for what would TV be without the hospital drama, and what would the hospital drama be without cap and masks and those long, meaningful stares?

The full regalia of the surgical operation did not escape a certain amount of gentle ridicule – in which we may hear the voice of those older, coarser surgeons whom Moynihan supplanted. Moynihan was once described as ‘the pyloric pierrot’, and upon seeing Moynihan’s rubber shoes a French surgeon is said to have remarked ‘Surely he does not intend to stand in the abdomen?’