Theories of Aging

Here is an interesting web site with a post on the statistics of dying and various theories of aging. Here's the simplest one to understand:

Imagine that within your body is an ongoing battle between cops and criminals. And, in general, the cops are winning. They patrol randomly through your body, and when they happen to come across a criminal he is promptly removed. The cops can always defeat a criminal they come across, unless the criminal has been allowed to sit in the same spot for a long time. A criminal that remains in one place for long enough (say, one day) can build a “fortress” which is too strong to be assailed by the police. If this happens, you die.

Lucky for you, the cops are plentiful, and on average they pass by every spot 14 times a day. The likelihood of them missing a particular spot for an entire day is given (as you’ve learned by now) by the Poisson distribution: it is a mere .

But what happens if your internal police force starts to dwindle? Suppose that as you age the police force suffers a slight reduction, so that they can only cover every spot 12 times a day. Then the probability of them missing a criminal for an entire day decreases to . The difference between 14 and 12 doesn’t seem like a big deal, but the result was that your chance of dying during a given day jumped by more than 10 times. And if the strength of your police force drops linearly in time, your mortality rate will rise exponentially.

This is the Gompertz law, in cartoon form: your body is deteriorating over time at a particular rate. When its “internal policemen” are good enough to patrol every spot that might contain a criminal 14 times a day, then you have the body of a 25-year-old and a 0.03% chance of dying this year. But by the time your police force can only patrol every spot 7 times per day, you have the body of a 95-year-old with only a 2-in-3 chance of making it through the year.

There is much more, including some nice graphs in the original posting. It is worth taking a peek.

I know it is a morbid subject, but it is a universal fact that underlines our "common" humanity... as in humus and where we all end up potted in the end.