90 MODERN IDEAS OF EVOLUTION 



CHAPTER IV 

 THE APPARITION OF SPECIES IN GEOLOGICAL TIME 



TllE doctrine of organic evolution, whether on the 

 principle of struggle for existence and natural selec 

 tion, or on the converse principles of physiological 

 selection and of progressive adaptation to external 

 conditions, is essentially biological rather than geo 

 logical, and has been much more favoured by biolo 

 gists than by those whose studies lead them more 

 specially to consider the succession of animals and 

 plants revealed by the rocks of the earth. These 

 have for the most part been content to observe the 

 apparition, or first appearance of species, without 

 inquiry as to their origin or the ultimate causes of 

 their introduction. Evolutionists, however, require a 

 great lapse of time for their processes, and thus 

 come into the discussions of geology. Their de 

 mands in this matter have been put in so terse and 

 clear a manner by a recent advocate that I shall 

 quote his words as a text or motto for this chapter : 

 4 If art can in a few years effect so great changes in 



