loS MODERN IDEAS OF EVOLUTION 



in temperate regions could enjoy six months of con 

 tinuous sunshine were eminently favourable to the 

 development of such plants, and were utilised for 

 the introduction of new floras, which subsequently 

 spread to the southward. Thus we see physical 

 changes occurring in an orderly succession and made 

 subservient to the progress of life, and we also sec 

 that, not the adverse conditions of struggle for exist 

 ence, but the favouring conditions of scope for ex 

 pansion, were, as might rationally be expected, the 

 accompaniments and secondary causes of new inbursts 

 of life. 



6. There is no direct evidence that in the course 

 of geological time one species has been gradually or 

 suddenly changed into another. Of the latter we 

 could scarcely expect to find any evidence in fossils ; 

 but of the former, if it had occurred, we might expect 

 to find indications in the history of some of the 

 numerous species which have been traced through 

 successive geological formations. Species which thus 

 continue for a great length of time usually present 

 numerous varietal forms, which have sometimes been 

 described as new species ; but when carefully scru 

 tinised they are found to be merely local and tem 

 porary, and to pass into each other. On the other 

 hand, we constantly find species replaced by others 

 entirely new, and this without any transition. The 

 two classes of facts are essentially different, though 

 often confounded by evolutionists ; and though it is 



