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, WQuld 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 
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." jThns natilie 
gives the hint, man acts upon it, and by the law of inherit- 
ance exaggerates the deviation. 
1 Living 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 
