for disbelief in the principle, while furthermore the results of experiments that have been undertaken to test its truth have been entirely negative.  Rats and mice have had their tails cut off to see if this mutilation would have its effect upon their young, and though this has been done for more than one hundred successive generations the length of the tail has not been altered.  Quite unconscious of the scientific problem, many human races have performed precisely similar experiments through centuries of time.  In some classes of Chinese, the feet of young girls have been bound in such a way as to produce a small, malformed foot, but this has not resulted in any hereditary diminution in the size of the feet of Chinese females.  Many other similar mutilations have been practised, as for example, the flattening of the skull of some North American Indians, but the deformity must be produced again with each recurring generation.  One after another, the cases that were supposed to give positive evidence have been reinvestigated, with the result that has been stated above.  It would seem, therefore, that heredity and congenital modification must play by far the greater part in the evolution of species.

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The doctrine of natural selection took form in the mind of Darwin mainly on account of three potent influences; these were, first, the geological doctrine of uniformitarianism proposed by Lyell, second, his own observations of wild life in many lands and his analysis of the breeder’s results with domesticated animals, and third, the writings of Malthus dealing with overpopulation.  As Darwin had read the works of Buffon, Lamarck, and Erasmus Darwin, his grandfather, who had written a famous treatise under the title of “Zoonomia,” he was familiar with the evidences known in his student days tending to prove that organic evolution was a real natural process.  Lyell’s doctrine of uniform geological history made an early and deep impression upon his mind, and it led him to ask himself whether the efficient causes of past evolution might not be revealed by an analysis of the present workings of nature.  As naturalist of the “Beagle” during its four years’ cruise around the world, Darwin saw many new lands and observed varied circumstances under which the organisms of the tropics and other regions lived their lives.  The fierce struggle for existence waged by the denizens of the jungle recalled to him the views of Malthus regarding overpopulation and its results.  These and other influences led him to begin the remarkable series of note-books, from which it is interesting indeed to learn how the doctrine of natural selection began to assume a definite and permanent form in his mind, as year followed year, and evidence was added to evidence.  And it is a valuable lesson to the student of science that for twenty-five years Darwin devoted all his time to the acquisition of facts before he gave his doctrine to the world in the famous “Origin of Species.”