DAR WINISM AND OTHER BRANCHES OF SCIENCE. 361 



believing natural selection to be the cause of species may 

 be lessened. Great as is the difference between a newborn 

 infant and a man of twenty, the one passes into the other 

 by such imperceptible gradations that the boy of this 

 Monday is hardly distinguishable from the boy of last 

 Monday or of next Monday. We thus see that if we 

 divide the growth of an individual man into one thousand 

 stages the passage from one stage to the next is almost 

 imperceptible. In the same way, if we subdivide the 

 growth of a species into a thousand parts or a million 

 parts, we shall have gradations quite comparable with 

 those we meet with in the ordinary variation from one 

 generation to the next. 



Nor is it hard to see how the process of natural selec- 

 tion has gradually produced diverging branches from the 

 parent stem. The variations which occur may be of use 

 to the organism in various ways. Among the progeny of 

 A single pair there may be two individuals, A and B, 

 which are specially favoured ; but they may be favoured 

 in different ways. A may have some increased facility in 

 catching his prey ; B, by his peculiar colour, or greater 

 activity, may have superior success in eluding his enemies. 

 The descendants of A will gradually from one generation 

 to the next strengthen and reinforce the special feature 

 which characterized A. The descendants of B will grow 

 more and more adapted for eluding their enemies. The 

 influence of natural selection is in both cases promoting 

 the survival of the fittest, but each generation will see the 

 consins more and more widely separated. In no case, in- 

 deed, would the process be so simple as that here described 

 multitude of circumstances will occur to complicate it ; 



