Herbert Spencer / by J. Arthur Thomson.

  • John Arthur Thomson
Date:
1906
Catalogue details

Licence: In copyright

Credit: Herbert Spencer / by J. Arthur Thomson. Source: Wellcome Collection.

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    be satisfactorily interpreted without regarding it as in great part an adaptive character. But while the rate of reproduction depends upon the constitution of the individual organism, modifiable within variable limits by the direct influence of food, warmth, and the like, the rate of increase or decrease in an animal or* plant population depends upon the wide and complex conditions of the entire animate and inanimate environment. In short, it is a function of the Struggle for Existence. When there are no checks to prolific multiplication a single Infusorian may become, in the course of a week, the ancestor of several millions, and the same is true of a Bacterium within a day. Huxley has com- puted that the progeny of single mother Aphis or green-fly, if they all lived a charmed life, would in a few months literally outweigh the population of China, which probably amounts to between two and three hundred millions. If there were no checks to increase, a few pairs of cod-fish and conger-eels would soon put an end to fishing and much else, by making the North Sea solid. And apart from problematical cases, every now and then, with locusts or voles, with rabbits in Australia, or sparrows in America, we get a vivid glimpse of what a “ spate” of life may mean. In the main, however, the river of life overflows its banks only locally and temporarily. An adjustment of the abundance of life to the limitations of subsist- ence is speedily effected in nature, and the flood subsides. The “ positive checks ” of disease, starva- tion, lack of room, internecine competition, increase of enemies, and so on, re-establish a balance, though per- haps with a slightly changed centre of gravity. The
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