DARWIN'S THEORY UNSHAKEN 31 



will be observed, is an inference, and not a direct obser- 

 vation. 



So long as the conditions remain practically or 

 effectively unchanged, the animal or plant already " fitted " 

 to them will be succeeded by those of its offspring which 

 most resemble it in the essential points of " fitness." But 

 we know that in the course of ages, more or less rapidly, 

 climates change, land emerges from the sea, islands join 

 continents, continents become scattered islands, animals 

 and plants migrate into regions previously uninhabited by 

 them. As such changes gradually come on, the natural 

 selection of favoured varieties will necessarily lead to the 

 survival of others than those previously favoured, other 

 variations better suited to the new conditions will survive. 



The natural selection of favoured variations would not 

 amount to much, were the variations not perpetuated by 

 transmission to the young which they produce. This, it 

 is common knowledge [see (3)], does take place. It is 

 known also that a variation so established is as a result 

 of the regular process of variation presented in larger 

 volume or emphasised in character in some individuals of 

 subsequent generations, and by continued " natural selec- 

 tion" it may become more and more a prominent or 

 dominant feature of the race. 



So far, the only assumption made by Mr. Darwin is 

 that any or some of the endless variations which occur in 

 all the offspring of wild plants and animals, in various 

 combinations and degree in each individual, can be 

 sufficiently important to determine the survival or non- 

 survival of the organisms possessing them. That is a 

 matter which has been largely studied and discussed. 

 The verdict of those who have studied on the spot (as 

 Darwin himself did) the teeming life of the tropics, the 

 insects, birds, and plants of those regions, is that we are 

 justified in considering that small variations are sufficiently 



