The bad news for big dogs does not end there. Many people buy health insurance for their pets so that their faithful companions do not bankrupt them as, in their dotage, the dogs require heart bypass surgery. Insurance companies, seeking as ever to minimise their risk, have collected vast databases on the health and mortality rates of their clients (the dogs, not the premium-paying humans) which show quite clearly that, independent of the risk of osteosarcoma, big dogs age faster than smaller dogs. Great Danes, Newfoundlands, and St Bernards have average lifespans of four to five years; Chihuahuas and toy poodles live about ten years longer. There are about four hundred distinct breeds of dogs: for every kilogram that one of these breeds is heavier than another, it loses eighteen days of life.
These results seem to tell us that large size is generally unhealthy, but it is just a correlation. Dog breeds differ from each other in so many ways that it is difficult to attribute differences in longevity among them to differences in size alone. Ten thousand years of dog breeding is a magnificent natural experiment, but like all natural experiments, it isn’t really an experiment at all – at least not in the sense of being a controlled manipulation. Fortunately, a real experiment is at hand: dwarf and giant mice. The mutant mice that are so small for want of growth hormone also live up to 40 per cent longer than their normal-sized brothers and sisters. Conversely, mice that are genetically engineered to be giant age fast and die soon. Whatever the causes of the inverse association between body size and ageing, it seems to be found in all mammals.
I am fascinated by these findings. If dogs and mice, why not people? Could it be that small people are genetically predisposed to live longer than taller people? Some scientists think so. They point to a family with defective pituitaries who live on the Adriatic island of Kruk and who seem to be (despite being both dwarfed and cretinous) rather longer-lived than the average Croatian. Or else to studies that show that the shortest American baseball players outlive taller ones by eight years. Maybe so, but the sample sizes in these studies are small, and large national surveys in Norway, Finland and Great Britain have consistently shown the opposite trend. This is hardly surprising. Socioeconomic factors account for most of a population’s variation in both height and health.
To be poor is to be both short and at higher risk of nearly any disease you care to name. This effect simply overwhelms any genetic tendency for the opposite trend, if such a tendency indeed exists. Will the poor always be short? Perhaps not. Young Dutchmen are, on average, 184 centimetres (six feet) tall. This makes the Dutch the tallest people in the world, taller even than Dinka goatherds or Masai morani. And they are getting taller: by 2012 their men will be 186 centimetres (nearly six feet one inch) tall, their women 172 centimetres (five feet seven inches). Recently, tall activists have even managed to persuade the Dutch government to raise – by twenty centimetres – the ceiling levels specified in that nation’s building codes.
This supremacy in centimetres is partly because Holland is a northern country rich in cows. Being northern, it has a population that tends to be genetically rather taller than, say, their southern neighbours the Belgians, who are in turn taller than their southern neighbours, the French. Dutch children also have a high consumption of animal protein – the product of all those placid black-and-white milk cows that give the Dutch landscape its characteristic look, and the Dutch atmosphere its characteristic tang. But Holland’s geographic peculiarities are probably not enough to explain the genial blond giants that can be seen in such numbers on its university campuses; for many years it has had a medical system that is excellent, efficient and egalitarian, if hard on its taxpayers’ wallets, and this must surely also contribute to the general stature of its young citizens. Most remarkably, it is no longer possible to judge the socio-economic background of Dutch children from their height. Decades of social engineering have eliminated the differences that have existed there (and everywhere else) for millennia. Égalité has begun to reach our very bones.
But not in most countries. Elsewhere, the rich remain tall and the poor short. Young Englishmen are, on average, 176 centimetres tall, a full eight centimetres shorter than young Dutchmen. England is also an exception to the rule that northern peoples are taller than southern ones. The inhabitants of Holland may be taller than the French, and the farmers of Schezwan taller than the Cantonese, but Yorkshire man is shorter than Essex man, and the average Scot is shorter yet. Celtic vs. Saxon genes may make a difference, but most public health experts point to the relative poverty of northern Britain. Notoriously, the inhabitants of some especially forsaken Glasgow council estates can travel for five kilometres in any direction without finding so much as a cabbage for sale.
The poverty and short stature of the north of England’s people is long-standing. More than 150 years ago, the northern cities of Leeds and Manchester became the site of the first serious investigation into the growth of British children when the social reformer Edwin Chadwick investigated the conditions of children working in the cotton mills. By modern standards, the factory children were remarkably small. Age-for-age, they were shorter than the shortest 3 per cent of modern British children, and the difference persisted, the average eighteen-year-old factory worker being only 160 centimetres (five feet three inches) tall. In 1833, the year that Chadwick published his report, the British Parliament passed a Bill against the employment of children under the age of nine.
It is precisely the antiquity of the positive association between health and height that probably accounts for the pervasive attractions of height. From George Washington to George Walker Bush there have been forty-three US presidents, and forty of them have been taller than the average American male. James Madison was famously only 164 centimetres (five feet four inches), but then he was also the architect of his nation’s constitution. Presidential candidates are not taller than the people they aspire to govern simply because they are wealthier. Voters actively choose height as welclass="underline" forty of the forty-three election-winners have been taller than their closest rivals. Women of all cultures seem to prefer men who are on average five centimetres (about two inches) taller than themselves. Professors, who may be expected to value the intellect above all things, behave in the same way. Full professors in American universities are on average three quarters of an inch taller than lowly assistant professors, and department chairmen are taller yet. When asked what height they should like to be, American men of even average height invariably wish themselves taller. And who can blame them?
The pervasive attractions of height present us with a dilemma. As we learn more about the molecular mechanisms that control height, we will be able to manipulate with ever greater subtlety the size that we, or rather our children, grow to be. But what size should we be? The boundary between normal and pathological height is never distinct: it is a grey zone, dictated by clinical possibility, or even convenience. There are, it is true, many diseases, genetic or otherwise, of which shortness is symptomatic. But shortness, even when genetic in origin, is not always, or even most of the time, a disease. In the United States, some thirty thousand short children are currently being given recombinant growth-hormone supplements to make them grow. Most of these children are growth-hormone deficient, and for these the treatment is quite appropriate. But about a third of them have what is called ‘idiopathic short stature’. That is, they are not short because they are malnourished, or because they are abused, or because they have anything identifiably, clinically, wrong with them – they are merely short. They are given growth hormone because their parents would like them to be taller.