Longevity

Longevity. The duration of life in different animals varies between very wide limits. Some insects live in their perfect form for a few hours only; while the elephant, eagle, carp, and other creatures attain, in some instances, an age considerably exceeding 100 years. For each species it appears that a limit of age, which is rarely exceeded, can be fixed; and when the individual member of the species lives for a longer period than that indicated it is said to present an instance of longevity. In man, the limit of the duration of life can be determined with some degree of exactness, at any rate so far as those countries are concerned in which an attempt to accurately register all deaths is made. English statistics show that considerably less than one-tenth of those born attain to the age of 80, while of 100,000 born less than 20 reach the age of 100. Careful inquiry has been made in recent years into the subject of centenarians, and it has been shown that those instances in which human life has been stated to considerably exceed the 100 year limit, are not well authenticated. A German man of science, Weismann, has recently discussed the question of the duration of life in its relation to the theory of Darwin. He maintains that the average length of life in each species is determined by the process of natural selection, and that the average duration of existence in the individual is largely determined by the length of time required by it to produce and rear its offspring to maturity.