Contributions to the Theory of Natural Selection: A Series by Alfred Russel Wallace

By Alfred Russel Wallace

Alfred Russel Wallace (1823-1913) is thought of as the co-discoverer with Darwin of the speculation of evolution. It used to be an essay which Wallace despatched in 1858 to Darwin (to whom he had devoted his most renowned ebook, The Malay Archipelago) which impelled Darwin to put up a piece of writing on his personal long-pondered idea at the same time with that of Wallace. As a traveling naturalist and collector within the some distance East and South the US, Wallace already susceptible in the direction of the Lamarckian concept of transmutation of species, and his personal researches confident him of the truth of evolution. at the book of at the starting place of Species, Wallace grew to become considered one of its so much popular advocates. This moment, corrected, version (1871) of a chain of essays released in ebook shape in 1870, exhibits the improvement of his brooding about evolution, and emphasises his admiration for, and aid of, Darwin's paintings.

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19 differ from the temperate zone in the uniformity of their climate. However this may be, it seems a, fair assumption that during a period of geological repose the new species which we know to have been created would have appeared, that the creations would then exceed in number the extinctions, and therefore the number of species would increase. In a period of geological activity, on the other hand, it seems probable that the extinctions might exceed the creations, and the number of species consequently diminish.

Our knowledge of the organic world during any geological epoch is necessarily very imperfect. Looking at the vast numbers of species and groups that have been discovered by geologists, this may be doubted; but we should compare their numbers not merely with those that now exist upon the earth, but with a far larger amount. We have no reason for believing that the number of species on the earth at any former period was much less than at present; at all events the aquatic portion, with which geologists have most acquaintance, was probably often as great or greater.

Wild cats are prolific and have few enemies ; why then are they never as abundant as rabbits ? The only intelligible answer is, that their supply of food is more precarious. It appears evident, therefore, that so long as a country remains physically unchanged, the numbers of its animal population cannot materially increase. If one species does so, some others requiring tho same kind of food must diminish in proportion. The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be INDEFINITELY FROM THE ORIGINAL TYPE 33 the weakest—the very young, the aged, and the diseased—while those that prolong their existence can only be the most perfect in health and vigour— those who are best able to obtain food regularly, and avoid their numerous enemies.

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