NATUEAL SELECTION. 99 



the opposite side, by considering the vast reduction of 

 brachiopods, and the fact that our existing cephalopods, 

 though few in number, are more highly organized than 

 their ancient representatives. We ought also to compare 

 the relative proportional numbers at any two periods of 

 the high and low classes throughout the world ; if, for 

 instance, at the present day fifty thousand kinds of ver- 

 tebrate animals exist, and if we knew that at some for- 

 mer period only ten thousand kinds existed, we ought 

 to look at this increase in number in the highest class, 

 which implies a great displacement of lower forms, as a 

 decided advance in the organization of the world. We 

 thus see how hopelessly diificult it is to compare with per- 

 fect fairness, under such extremely complex relations, the 

 standard of organization of the imperfectly-known faunas 

 of successive periods. 



Ori^n of There may truly be said to be a constant 



Species, struggle going on between, on the one hand, 



the tendency to reversion to a less perfect 

 state, as well as an innate tendency to new variations, 

 and, on the other hand, the power of steady selection to 

 keep the breed true. In the long run selection gains the 

 day, and we do not expect to fail so completely as to 

 breed bird as coarse as a common tumbler-pigeon from a 

 good short-faced strain. But, as long as selection is rapidly 

 going on, much variability in the parts undergoing modi- 

 fication may always be expected. 



A HIGHEE WOKKMAKSHIP THAN MAK'S. 



Ori • of ^® ^^'^ '^^^ produce, and certainly has 



SpedeB, produced, a great result by his methodical and 



page 66. unconscious means of selection, what may not 

 natural selection affect ? Man can act only on external 



