I pointed out an article on life expectancy statistics last week, and said:

What benefits to life span have been incidentally derived from advances in medical technology? I think we're all aware of the underlying reasons for large gains in life expectancy - but comparatively little has been gained in the extension of healthy old age: "In 1900, the average 65-year-old could expect another 12 years of life, on average. A century later, in 2000, life expectancy post-65 had increased to 19 years for women and 16 years for men. Similarly, in 1900, 85-year-old Americans could expect an additional four years of life. By 2000, that statistic increased seven years for women and six years for men." Clearly, incidental life extension only gets us so far - we need more directed research into the untreated mechanisms of aging.

In a private e-mail, Ian Clements elaborates on the figures:

The Forbes article you quote appears to miss the point about increasing longevity. The apparent near-doubling of Western lifespans over a century or so is, to a large extent, a statistical trick, implying the average person now lived twice as long - well, yes, if the average includes the new-born. It was the high death rate of the latter that has dramatically fallen, giving rise to the apparant doubling lifespan. But for an adults, lifespans haven't doubled.

But they have STEADILY increased - and THAT is the point. There is a linear increased lifespan for all adult ages, including the very old, over the recorded couple of centuries we've had figures. This is the basis for maintaining that there is no 'natural' upper limit; if there was, then the increase in lifespans would be levelling off.

So don't let's worry that the increases are small, but note that they are continuously linear (or even increasing). This gives hope that we can uncover the mechanisms which cause steady degeneration, and slow or reverse them.

The Reliability Theory of Aging is a good introduction for newcomers who want to place the historical extension of longevity - and thoughts about limits on life span, or lack thereof - within a scientific framework:

"We are like machines made up of redundant components, many of which are defective right from the start." Machine failure rates and human death rates are very similar in form - which should not be too surprising. Reliability theory predicts no fixed upper limit to life span: "Even small improvements to the processes of early human development - ones that increase the numbers of initially functional elements - could result in ... a significant extension of human life."

Within the framework of Reliability Theory, we can suggest that gains in life expectancy in old age are incidental - they result from reductions in bodily damage due to chronic disease. As advances in medicine eliminate or minimise diseases that plagued our ancestors, we benefit as the complex machines that are our bodies run better, for longer.

It's still past time to get to work on directed research into real anti-aging medicine, however. The incidental rate of increase of healthy life span is far too slow for my liking.

Posted by Reason at November 24, 2004 7:14 PM | TrackBack (0)