A Means to an End: The Biological Basis of Aging and Death
| Date: 15 April 2011, 15:21
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Professor Clark writes with elegance and employs a reasoned tone, but he is not always direct, and often expresses ideas in the understandably tentative way of a very exacting scientist. Consequently it is not easy to see that nowhere in this book does he directly say what causes aging and death. Nor does he simply say we don't know. What he does say is there are some persuasive theories, especially the evolutionary model began by Haldane and Medawar and refined by George Williams (pp. 49-50), that are consistent with the data that "may be essentially correct, at least in broad outline." (p. 52). Clark makes it clear that we have senescence effector genes in our cells but he doesn't say how they got there, only that they were "already in place in the earliest eukaryotic organisms such as paramecia and yeast." (p. 57) The reader is left to believe that there is a mechanism that retains them, but what that mechanism might be is unclear.
I am led to believe that senescence is built into our cells and is part of our genetic makeup. We are programmed to grow old and die. Just how is what Professor Clark is exploring here. He concentrates on the cellular level because it is his belief that this is where the mechanisms for senescence can be found. On page 190 he argues that senescence is genetically controlled and not the result of a random breakdown, citing the fact that "maximum lifespan is species-specific." In short, humans live a lot longer than dogs, contrary to what might be expected if senescence were caused by cells getting old and wearing out. He points out on page 48 that "mice and humans, although composed of proteins that are extremely similar at a chemical level, have both average and maximal lifespans differing by a factor of 30 or more."
Clark also covers in some detail such issues as the evolution of senescence, average and maximum lifespan; genetic diseases such as Werner's syndrome, the Hutchinson-Gilford syndrome and others; oxidative stress as a cause of cellular senescence and the use of Vitamin E and other antioxidants; the aging brain and Alzheimer's disease; cancer and the social and economic effect of humans living longer. A chapter is devoted to the phenomenon of increased lifespan through restricted caloric intake.
This is an authoritative and persuasive book, well written and well presented.
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