474 FRAGMENTS OF SCIENCE. 



with what could, without any manner of doubt, be done 

 in the way of producing variation. 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 directed to 

 the particular appearance which he wishes to exaggerate, 

 he selects it as it reappears in successive broods, and thus 

 adds increment to increment until an astonishing amount 

 of divergence from the parent type is effected. The 

 breeder in this case does not produce the elements^ of the 

 variation. He simply observes 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 

 fautail 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 inherit- 

 ance exaggerates the deviation. 



Having thus satisfied himself by indubitable facts that 

 the organization 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 selection 

 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 sup- 

 ported; hence at some period or other of their lives there 

 must be a struggle for existence. And what is the infal- 

 lible 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 sur- 

 rounding conditions will infallibly give way to those that 



