Page:Darwinism by Alfred Wallace 1889.djvu/435

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evolution, and especially on Darwin's presentation of that theory, to the bewilderment of the general public, who are quite unable to decide how far the new views, even if well established, tend to subvert the Darwinian theory, or whether they are really more than subsidiary parts of it, and quite powerless without it to produce any effect whatever.

The writers whose special views we now propose to consider are: (1) Mr. Herbert Spencer, on modification of structures arising from modification of functions, as set forth in his Factors of Organic Evolution. (2) Dr. E.D. Cope, who advocates similar views in detail, in his work entitled The Origin of the Fittest, and may be considered the head of a school of American naturalists who minimise the agency of natural selection. (3) Dr. Karl Semper, who has especially studied the direct influence of the environment in the whole animal kingdom, and has set forth his views in a volume on The Natural Conditions of Existence as they Affect Animal Life. (4) Mr. Patrick Geddes, who urges that fundamental laws of growth, and the antagonism of vegetative and reproductive forces, account for much that has been imputed to natural selection.

We will now endeavour to ascertain what are the more important facts and arguments adduced by each of the above writers, and how far they offer a substitute for the action of natural selection; having done which, a brief account will be given of the views of Dr. Aug. Weismann, whose theory of heredity will, if established, strike at the very root of the arguments of the first three of the writers above referred to.

Mr. Herbert Spencer's Factors of Organic Evolution.

Mr. Spencer, while fully recognising the importance and wide range of the principle of natural selection, thinks that sufficient weight has not been given to the effects of use and disuse as a factor in evolution, or to the direct action of the environment in determining or modifying organic structures. As examples of the former class of actions, he adduces the decreased size of the jaws in the civilised races of mankind, the inheritance of nervous disease produced by overwork, the great and inherited development of the udders in cows and goats, and the shortened legs, jaws, and snout in