NATURAL SELECTION 117 



be more likely to survive than those which have not 



the variation in question. They will in this way 



be " naturally selected from among the sum total of 



individuals of that generation," much in the same 



way as certain plants and animals are, artificially, 



i.e., consciously, selected by man, on account of their Natural 



possessing some feature of service to him or agreeing selection - 



with his taste. 



An illustration will make this subject clearer. Let 

 A be an organism say a plant adapted to ordinary 

 terrestrial conditions ; it will give rise, in any particu- 

 lar year, to, say, 100 seeds. These seeds will be 

 scattered far and wide, but some may get eaten, 

 some may fall on rock, some on water, and none of 

 these will germinate. Let us suppose that ten get 

 planted in situations which are, on the whole, suitable 

 for their germination. Of these, a, let us say, ger- 

 minates at the bottom of a moist ditch, while 6 

 germinates on fairly dry arable soil. Both develop 

 into seedlings and thus start two new centres of 

 colonisation for A. a gives rise in like manner to 

 progeny, and let us assume that the variations shown 

 by a', one of a's progeny, are such as to enable it to 

 make a home satisfactorily under moister conditions 

 than A or a, and that b also gives rise to progeny, one of 

 which, &', is better adapted to live under drier con- 

 ditions than A or 6. If these conditions are main- 

 tained for a series of generations, the aquatic cha- 

 racters of the a! series will become emphasised, just 

 as the characters of the b' series will gradually become 

 more and more suited to dry conditions. Manifestly, 

 in the competition for space, the original a and 6 

 types are likely to die out and be replaced by the 

 types a' and b' ; b' and a' have thus been naturally 

 selected out of a series represented at the extremes 



