The signs of old age are no more profuse than the theories attempting to explain its cause or causes. This is hardly surprising, for no common denominator has been found as yet. There is not even agreement as to how many years constitute man’s natural life span. Each plant or animal has a maximum life expectancy, which cannot be exceeded even if the organism remains healthy. The fact that almost no one dies of old age per se would indicate that most of us never reach our full potential. But what is our potential life span? Biologists measure it against the time maturity is achieved or bones stop growing in length, and their resulting figures are that man should live for 120 to 150 years! But no generally accepted criteria exist: man’s natural life span is still a matter of speculation.
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