Richard Dawkins, The Selfish Gene
Senile decay is simply a by product of the accumulation in the gene pool of late acting lethal and semi lethal genes, which have been allowed to slip through the net of natural selection simply because they are late acting…
If we wanted to increase the human lifespan, there are two general ways in which we could do it. Firstly, we could ban reproduction before a certain age, say 40. After some centuries of this the minimum age limit would be raised 50, and so on. It is conceivable that human longevity could be pushed up to several centuries by this means. I can't imagine that anyone would seriously want to institute such a policy.
Secondly we could try to fool genes into thinking that the body they are sitting in is younger than it really is. In practice this will mean identify changes in the internal chemical environment of a body which takes place during aging. Any of these could be the cues which turn on late acting lethal genes. By stimulating the superficial chemical properties of your body it may be possible to prevent the turning on of late acting deleterious genes.
In the actual duration of his life, the individual ranges from the bacterium's hour to the big tree's five thousand years.
- Julian Huxley