xm NATURAL SELECTION 227 



the conditions to which they are subject. According to 

 Darwin's theory of natural selection, it is assumed that 

 such surviving individuals would transmit their special 

 properties to their progeny, and there would thus be a 

 gradual approximation towards a perfect adaptation of 

 the species to its surrounding conditions by virtue of 

 this " survival of the fittest/' 



Let us suppose he conditions to change. Gradual 

 alterations in climate and other conditions are known to 

 take place, owing to subsidence or elevation of the land. 

 But conditions might be changed in many other ways : 

 some animal or plant previously used as food might 

 become exterminated, or a new enemy might find its way 

 into the district inhabited by the species. Then such 

 individuals as presented variations which enabled them 

 better to cope with the new surroundings would have 

 the advantage over the others, and would have a much 

 better chance of surviving and leaving progeny. The 

 useful variations thus produced and transmitted to the 

 progeny would tend to increase, generation after 

 generation, until a form sufficiently distinct to be re- 

 garded as a new species had become developed from 

 the original one. 



That very different varieties of animals and plants 

 can, and have been produced, in a comparatively short 

 time, by man selecting those forms which tend to vary 

 in a desired direction, is a well-known fact. All the 

 breeds and varieties of our domestic animals have been 

 produced by this process of artificial selection ; and " if 

 man can by patience select variations useful to him, 

 why, under changing and complex conditions of life, 

 should not variations useful to Nature's living products 

 often arise, and be preserved or selected ? " 



It does not come within the scope of the present work 



Q 2 



