Since Aristode, numerous studies have confirmed that reproduction exacts survival costs in a variety of creatures. The severity of these costs at the limit is shown by Antechinus stuarti, an Australian marsupial mouse. For the males of these mice, existence is little more than sex. Their brief adult lives consist of fighting other males, wandering about in search of females and, when they find them, engaging in exhausting twelve-hour-long copulations repeated daily for nearly two weeks. Perhaps unsurprisingly, after a single mating season they are dead, their tissues showing all the signs of catastrophic senescence. By the time they are done, they are devoid of sperm, their prostate glands have shrivelled up, their testes have become invaded by connective tissue, their adrenal glands are hypertrophied, their livers necrotic, their gastric tracts are haemorrhaging, and their penises are quite flaccid.
Marsupial mice are an especially blatant illustration of the idea that ageing is the consequence of youth’s excesses. But there is evidence that the same economic principle affects humans, albeit to a more modest degree. The British have, of course, no Pilgrim Fathers to genealogise. Instead they have an aristocracy, mostly dating from Norman times, whose singular, indeed defining, virtue is an obsession with their own line of descent. Traditionally, the genealogies of Britain’s noble houses have been recorded in the volumes of Burke’s peerage, but these days a handier account of the pedigrees of most British peers, from the Dukes and Earls of Abercorn to the Barons of Willoughby de Broke, is available on CD-ROM. This database, which stretches back to 740 AD, contains, in so far as they are known, the birth dates, marriages, and progeny of the British nobility, and has been used to test the idea, evident to the parents of any newly born infant, that having children takes years off your life.
Before the Industrial Revolution, the wife of a British peer could expect to live to the age of forty-five. She could also expect to bear two or three children. These averages, however, conceal much variety in the chances of life. Some women died young, and so had very few children. Some died in the decade or two after menopause (fifty to sixty): on average they had 2.4 children. But some – albeit rather few – survived past age ninety. These elderly women had had, on average, only 1.8 children, and nearly half of them were childless.
This is a fascinating result. Not only is it consistent with the results of the fruit fly experiments, it suggests that had Alexander Graham Bell’s dreams ever come to fruition, his gerontocrats would have had an ever dwindling fertility. A more sobering thought is that many, though surely not all, aspects of the senescent decline of our later years may be difficult to meliorate without damping down the physiological and sexual excesses of youth. In the future, humans may well be able to engineer themselves, be it by better drugs or better genes, to live as long as they please, but the cost may be twenty-year-olds with all the vigour, appetites and charm of the middle aged.
LA VITA SOBRIA
Is there a recipe for long life? Luigi Cornaro thought there was. In 1550, the Venetian nobleman published a tract called Discorsi della vita sobria (Discourses on the sober life) in which he outlined the regime that had ensured his own longevity. He was probably eighty-three at the time, and lived until ninety-eight or 103 – there is some dispute about his birth date, though all agree that he reached a great age. By his own account he had, until the age of forty, lived a life of sensual dissipation. The consequences were pains in the stomach and side, gout, fever, and an unquenchable thirst. His physicians warned him that he must reform or die. He took their advice to heart and thenceforth devoted himself to a temperate and orderly way of life.
The chief ingredient of his new regime was simple: eating less, and then only what he found agreeable. ‘Not to satiate oneself with food is the science of health,’ he wrote. He is vague on specifics, but at the one point at which he reveals what his actual diet was, it does not sound too arduous. A typical meal would begin with bread, then a light broth, perhaps with an egg. But, he said, ‘I also eat veal, kid and mutton; I eat fowls of all kinds, as well as partridges and birds like the thrush. I also partake of salt-water fish as the goldney and the like; and, among the ovarious fresh-water kinds, the pike and others.’ A modest diet by sixteenth-century Italian standards then. Yet at one point he grew so thin that his friends urged him to eat more. Cornaro’s oracular reply was that whosoever wished to eat long must eat little.
This is a little smug, but the Vita sobria charms – Cornaro is so clearly delighted by his longevity. A portrait by Tintoretto shows him in his splendid dotage, a grave and fine-featured patrician with skin made translucent by age. Cornaro spent his last years at his Paduan palazzo with its decorations by Raphael and at his villa in the Euganean Hills by the River Brenta with its exquisite gardens and fountains. ‘I did not know,’ he writes, ‘that the world could be so beautiful until I was old.’
The Vita sobria was a huge success. As he grew older, Cornaro added material to its successive editions: two, three, and finally four discorsi. A product of the Italian Renaissance, the book’s style was classical (Jacob Burckhardt cited it for its perfection), its physiology Aristotelian (much about moisture loss), and its sentiments Ciceronian (old age is a thing to be welcomed, a time of wisdom when passions have been burnt away). Its influence was long-lasting and can be found, for example, in the writings of the German physician Christian Hufeland, whose Makrobiotik (1796) outlines the theory from which every modern health-food fad ultimately derives.
The worst of it is that there is an element of truth in Cornaro’s claim that the route to great longevity is eating less. By this I do not simply mean the sort of diet that will stave off gross obesity or even middle-age spread, but serious dieting of a sort that few people could sustain voluntarily. The only reliable way to extend the general physiological life of a mammal is to give it no more than two thirds of the daily calories that it wants. Dozens of studies have shown that ‘caloric-restricted’ mice live anywhere between 10 and 50 per cent longer than those which are allowed to eat as much as they want. Age for age, they are friskier, glossier and healthier than their controls. And they are slimmer: about half the weight of controls. Caloric-restricted mice do, of course, eventually die, but the ages at which they get diabetes, infections, renal malfunctions, autoimmune attacks, musculoskeletal degeneration, cardiomyopathy, neural degeneration and, most amazing of all, cancer are all delayed. Studies on rhesus monkeys are now under way to see if caloric restriction extends life in primates, but it will be another decade before we know the answer.
Uncertainty has not stopped many neo-Cornarists from committing themselves to lives of rigorous dieting. Caloric restriction has become a health fad like any other, with its own books and gurus. The diet usually consists of about a thousand calories per day, which is necessarily supplemented with a battery of vitamins and minerals. A thousand calories is about the minimum number needed to sustain the life of an average-sized man, though not enough to sustain his sex drive (or, to judge by pictures, his sex appeal). Whether these ultra-puritans will reap their reward is an open question. The severe caloric restriction experienced by the Dutch population during the Hongerwinter of 1944–45 certainly had no detectable beneficial effect on the long-term mortality rates of the survivors, but it could be argued that it takes decades of near-starvation for its virtues to become apparent.