By Rudi Westendorp, University of Copenhagen.
It might seem too simplistic to equate old people with old cars, but the comparison is a valid one.
Everything ages. It is the accumulation of damage that we incur simply by being here. As with cars, our bodies break down with time, not because of any manufacturing defect, but due to wear and tear. The damage suffered by our biological machines over the years, makes them liable to break down even at normal, moderate levels of use. Such appliances are simply old and in need of repair.
Charles Darwin understood this. From a biological perspective, there is no reason for us to get old. Humans need to reproduce and care for their children, so that they – in turn – can reach maturity and produce offspring of their own. It is not us but the DNA, the blueprint for our bodies, that creates an “eternal” life cycle, something that Darwin called fitness. Therefore we are all subject to strict biological programming to conceive, bear, and raise children. And of course to have sex.
Around age 40 to 50, our body begins to deteriorate. Permanent strains and greying hair are just the beginning, soon followed by glasses and hearing aids. Women become infertile, and other losses in function leave us needing pacemakers and hip replacements.
All this biological degradation happens as our useful life is over, at least in the evolutionary sense. Darwinian logic is no different than economy; it is much more profitable to invest available resources in youth and sex than keeping up repairing bodies that will ultimately fail.