Biological Mechanisms Underlying the Aging Process: The Ideas and Techniques of Genetics Are Being Used to Obtain New Insight into the Problems of Aging

Howard J. Curtis

Abstract: In this article the several theories put forward to explain the biological mechanisms underlying the aging process are examined. The only ones which attack the problem from the point of view of basic biological mechanisms are the wear-and-tear theory and the somatic mutation theory. The finding that radiation accelerates the aging process is a potent tool for attacking the problem experimentally. Experiments with mice specifically designed to verify the wear-and-tear theory showed conclusively that stress per se does not contribute to aging, and no experimental evidence could be found to support the theory.

On the other hand, a great deal of evidence now available indicates that mutations in somatic cells play a dominant role in aging. It is further shown that the organs having cells which frequently undergo cell division take part in the aging process very little, if at all. Organs having cells which seldom, if ever, divide have no opportunity to throw off either spontaneous or induced mutations, and it is these organs which are responsible for the aging of the animal. Spontaneous mutations build up at a rapid rate in these organs. A cell may continue to function normally long after it has suffered a deleterious mutation, and this accounts for much of the delay in the expression of radiation damage. It is suggested that the mutation rates for somatic cells are very much higher than the rates for gametic cells, and that this circumstance insures the death of the individual and the survival of the species.

Reproduced with permission from Science. Copyright 1963 American Association for the Advancement of Science.