There is no cancer which affects "the old" predominantly. The chances stay pretty much the same (with some exceptions). Also, at some age beyond 60, cancer stops being the main medical cause of death, being replaced by infections.

I also don't subscribe to the theory that individuals have to procreate to boost the survival of their genes. In reality it's a bit more complex than that, and even very old people can and do contribute to the survival of their children or their close relatives.

> In reality it's a bit more complex than that, and even very old people can and do contribute to the survival of their children or their close relatives. That's true for human beings. But for most species that is not true. Maybe that's why we are better at longevity than other species (http://www.medcan.com/articles/a_finite_number_of_heart_beat...). But we still have millions of years of evolution that say that it is better to be able to live short and intense than to be able to live long and die before achieving that of disease, predators, etc. Why nature will invest in an extreme long lifespan that is not going to happen? So for most species what happens to you as you grow old is not very important and other traits will be selected before lifespan by evolution.

I would not subscribe to the statement about what "the evolution says". Evolution does not produce the "best" individuals, it just drives population towards a local maximum in their particular environment, from their particular starting point. And that may mean a long life span or a short life span.