Biological practical jokes

I have read that there are two known ways of significantly extending life expectancy: one applies to the individual, the other to an entire species.

In the individual, the one known method of life extension is to restrict caloric intake to a level just above that of starvation and malnutrition. That's it. Eat less, live longer. But a lot less. Well below the level at which you would say your diet is ridiculously restrictive. So individuals on the brink of starvation enjoy the benefit of having longer lives during which they can probably look forward to continuing to live on the brink of starvation.

The one known way of increasing the general life expectancy of a larger population, or a species, is to restrict reproduction to those individuals of advanced age who are capable of reproducing. The idea behind this is that fatal diseases that manifest themselves in the earlier parts of an individual's life will tend to remove the individuals who carry them or are susceptible to them before they have a chance to pass on their susceptibilities to their offspring. (This is not, of course, true of all diseases. Huntington's disease tends to manifest itself in adults in their 30's and beyond, according to this Wikipedia entry.) After many generations, so the theory goes, more and more early-onset diseases will be removed, and children will inherit their parents' ability to reproduce at a more advanced age. (Apparently, this has been successfully demonstrated with fruit flies, where restricting reproduction is simply a matter of destroying the first few batches of eggs that are laid. With humans, even more unpleasant solutions would probably be required.)

But there's a rub. Several studies - including a recent study by a team of British and Swedish researchers reported in New Scientist - have indicated a relationship between the age of a child's father and the likelihood that those children will develop schizophrenia later in life. The older the father, the greater the chances. So we are faced with the prospect of populations spawning legions of long-lived but dangerously insane individuals.

Fortunately it's difficult to regulate reproduction in a free and open society. Teenage pregnancies may very well be a major factor in offsetting any ill effects of the current trend toward couples postponing having children until they are sufficiently established and comfortable with their careers. Having a saner but shorter-lived population is probably preferable to having a population with a greater number of schizophrenics with an overall longer life expectancy.

And as for near-starvation...well, you can keep that, too. I'd rather see people be happy and well-fed than living prolonged lives of misery. Some things come with too high a price.