Biology / by Patrick Geddes and J. Arthur Thomson.

  • Geddes, Patrick, Sir, 1854-1932.
Date:
[1925]
Catalogue details

Licence: Public Domain Mark

Credit: Biology / by Patrick Geddes and J. Arthur Thomson. Source: Wellcome Collection.

    196/268 (page 188)
    fishes, by which it is possible to tell the age to a year, just as in the case of trees. But while the reading of this scale-calendar is easy in the case of the salmon, it is very difficult in that of the herring; and experts differ with ichthyological fervour. What determines such varying spans of life ? There are two kinds of answer; supplemen¬ tary, not antithetic. The first lays emphasis on physiological factors. On the one hand, there are long-lived constitutions, marked by abundant anabolic storage, a smoothly- working endocrine system, resting habits, and not too costly reproduction. On the other hand, there are short-lived constitutions, relatively more katabolic, with little or no storage, often living dangerously, and with modes of reproduction that severely tax resources. The other kind of answer— strongly represented by Weismann—regards the length of life as determined by Natural Selection; since in given conditions those types would survive that have their duration of life adjusted to their chances of death and to their rate of effective multiplication. Forms that lived too long and continued to multiply when on the downgrade would automatically come to an end. Every life-insurance office knows of different normal lengths of life in mankind, as notably for the two sexes, and for different races also; but the phases of life also vary according to constitution and temperament. There are individuals with prolonged youth (and to-