Getting Old

Getting old is apparently a matter of biological accounting. Let me explain...

1. In the wild animals do not (generally) get old. This is because 'the wild' is wild and therefore dangerous and so the animals die before ever reaching old age.

2. The body has to spend a certain percentage of the energy it consumes on maintainence and repair, because in the general course of chemical reaction within the body damage is done to the cells which must be repaired. The question then becomes- How much energy should be spent on these repairs?

3. Think of it this way, you have a new building, each year you have a budget to spend on repairs. If you spend £100 per year on maintenance then the building would be uninhabitable after just one year. If you spend £3000 per year you would keep it in much better condition but eventually after 30 years the building would accumulate enough faults to be uninhabitable. Spend £10,000 and it would last 100 years. Spend a cool £1,000,000 per annum however would ensure the building would last forever.

4. Only it turns out that on average a building will be pulled down by eager developers after only 30 years, so it would be a waste of money to spend any more than £3000 per year on maintenance.

5. The same applies to us, throughout our evolution we were expected to live on average just 33 years from birth, 39 if we reach 15, and 54 if we reached 39. (1).

6. So how much energy should the human body put into repair given that we most likely be dead in our 30s. Well just enough to keep us going strong till then. After which point the accumulation of faults left unrepaired would begin to take their toll.

7. Combine this with the fact that the short life span meant that natural selection has been largely blind to genetic disorders that are triggered by old age, because people had breed and died of other causes before their genetic predisposition to Alzheimer's or Parkinsons prevented them from having children. Meaning that these traits would be less likely to be weeded out and are therefore still very much present in our genetic make up and...

Voila- Old Age.

(1) Hillard Kaplan, ect. al, in "A Theory of Human Life History Evolution: Diet, Intelligence, and Longevity" (Evolutionary Anthropology, 2000, p. 156-185, - http://www.soc.upenn.edu/cours...