672 THE POPULAR SCIENCE MONTHLY. 



the great mass of them held that never by any amount of internal or 

 external change, nor by the mixture of both, could the offspring of the 

 same progenitor so far deviate from each other as to constitute differ- 

 ent species. The function of the experimental philosopher is to com- 

 bine the conditions of Nature and to produce her results ; and this was 

 the method of Darwin.^ He made himself acquainted with what could, 

 without any manner of doubt, be done in the way of producing vari- 

 ation. He associated himself with pigeon-fanciers — bought, begged, 

 kept, and observed every breed that he could obtain. Though derived 

 from a common stock, the diversities of these pigeons were such that 

 " a score of them might be chosen which, if shown to an ornithologist, 

 and he were told that they were wild birds, would certainly be ranked 

 by him as well-defined species." The simple principle which guides 

 the pigeon-fancier, as it does the cattle-breeder, is the selection of 

 some variety that strikes his fancy, and the propagation of this variety 

 by inheritance. With his eye still upon the particular appearance 

 which he wishes to exaggerate, he selects it as it reappears in succes- 

 sive broods, and thus adds increment to increment until an astonishing 

 amount of divergence from the parent type is effected. Man in this 

 case does not produce the elements of the variation. He simply ob- 

 serves them, and, by selection, adds them together until the required 

 result has been obtained. " No man," says Mr. Darwin, " would ever 

 try to make a fantail till he saw a pigeon with a tail developed in some 

 slight degree in an unusual manner, or a pouter until he saw a pigeon 

 with a crop of unusual size." Thus Nature gives the hint, man acts 

 upon it, and, by the law of inheritance, exaggerates the deviation. 



Having thus satisfied himself by indubitable facts that the organ- 

 ization of an animal or of a plant (for precisely the same treatment 

 applies to plants) is to some extent plastic, he passes from variation 

 under domestication to variation under Nature. Hitherto we have 

 dealt with the adding together of small changes by the conscious se- 

 lection of man. Can Nature thus select ? Mr. Darwin's answer is, 

 "Assuredly she can." The number of living things produced is far 

 in excess of the number that can be supported ; hence at some period 

 or other of their lives there must be a struggle for existence ; and 

 what is the infallible result ? If one organism were a perfect copy of 

 the other in regard to strength, skill, and agility, external conditions 

 would decide. But this is not the case. Here we have the fact of 

 variety offering itself to Nature, as in the former instance it offered 

 itself to man ; and those varieties which are least competent to cope 

 with surrounding conditions will infallibly give way to those that are 

 competent. To use a familiar proverb, the weakest comes to the wall. 

 But the triumphant fraction again breeds to over-production, trans- 



^ The first step only toward experimental demonstration has been taken. Experi- 

 ments now begun might, a couple of centuries hence, furnish data of incalculable value, 

 which ought to be supplied to the science of the future. 



