A Rolls-Royce lasts far longer than a Volkswagen bug, but its cost per mile is far higher than that of the bug, too. To engineer self-repair capabilities and to use long-lived components is generally more expensive than to
use shorter-lived, disposable units. This is why deep space probes such as Viking, Pioneer, and Voyager are so astronomically expensive. In a similar fashion, biological systems do not feature perfect repair mechanisms.
They must have repair systems adequate to ensure survival to adulthood, reproduction, and, in higher animals, the rearing of young to adulthood
at a rate at least equal to the death rate, or the species will quickly die out under natural conditions. Complex repair mechanisms able to preserve human life for hundreds of years would (we presume) be a less cost-effective means of making gene copies than our present limited life span.
Scientist Thomas Kirkwood looks at it this way: The body is a disposable package carrying the genes. The package is “designed” (evolves) to facilitate the genes’ making copies of themselves. A short-lived disposable package is a more efficient use of scarce resources for gene reproduction than a longer-lived package. The interests of the package (you, the individual carrying the genes) can be quite different from the interests of the genes, which is to make copies of themselves. Birth control is an explicit recognition of this fact.
Another example:
The temperatures yielding the longest life spans in fruit flies and nematodes (roundworms) are not the same as the temperatures resulting in the optimal production of offspring (gene copies).
The temperature yielding the maximum life span gives about half the number of viable offspring as the optimum reproductive temperature. Here is another case of the “selfish gene” in action; what is best for making a lot of gene copies (offspring) is not necessarily best for the individual. See
The Selfish Gene by Richard Dawkins (Oxford University Press, 1976) for a fascinating discussion of this type of conflict.
Dr. Gerald P. Hirsch, a mathematical biologist, has shown, for a species reproducing to the end of its life span— as most do in the wild—that the life span increases to just that point where the reproductive advantage of additional life span is just offset by the reproduction disadvantage of the in-
creased reproductive mutation level.
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