A world of Methuselahs
June 25th 2009
Angus Maddison, an economic historian, has estimated that life expectancy during the first millennium AD averaged about 25 years (which in practice meant that lots of children died very young and many of the rest survived to middle age). The big turnaround came with the industrial revolution, mainly because many more children survived into adulthood, thanks to better sanitation, more control over epidemics, improved nutrition and higher living standards.
By the beginning of the 20th century average life expectancy in America and the better-off parts of Europe was close to 50, and kept on rising. By mid-century the gains from lower child mortality had mainly run their course. The extra years were coming from higher survival rates among older people. The UN thinks that life expectancy at birth worldwide will go up from 68 years at present to 76 by 2050 and in rich countries from 77 to 83. (These are averages for both sexes; women generally live five or six years longer than men, for reasons yet to be fathomed). Most experts now agree that there will be further rises, but disagree about their extent.
Some of them argue that the human lifespan is finite because bodies, in effect, wear out; that most of the easy gains have been made; and that the rate of increase is bound to slow down because people now die mostly of chronic diseases – cancer, heart problems, diabetes – which are harder to fix. They also point to newer health threats, such as HIV/AIDS, SARS, bird flu and swine flu, as well as rising obesity in rich countries – to say nothing of the possibility of fresh pandemics, social and political unrest and natural disasters.
Nearly 30 years ago James Fries at Stanford University School of Medicine put a ceiling of 85 years on the average potential human life span. More recently a team led by Jay Olshansky at the University of Illinois at Chicago said it would remain stuck there unless the ageing process itself can be brought under control. Because infant mortality in rich countries is already low, they argued, further increases in overall life expectancy will require much larger reductions in mortality at older ages. In Mr. Olshansky’s view, none of the life-prolonging techniques available today – be they lifestyle changes, medication, surgery or genetic engineering – will cut older people’s mortality by enough to replicate the gains in life expectancy achieved in the 20th century.
That may sound reasonable, but the evidence points the other way. Jim Oeppen at Cambridge University and James Vaupel at the Max Planck Institute for Demographic Research in Rostock have charted life expectancy since 1840, joining up the figures for whatever country was holding the longevity record at the time, and found that the resulting trend line has been moving relentlessly upward by about three months a year. They think that by 2050 average life expectancy in the best-performing country could easily reach the mid-90s.
One of the reasons that backs the belief that human lifespan is finite, according to some experts, is that
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