288 STATE OF DEVELOPMENT OF [CHAP. XL 



fessor Pictet in his belief in the immutability of species. He who 

 is acquainted with the distribution of existing species over the 

 globe, will not attempt to account for the close reseaiblance of 

 distinct species in closely consecutive formations, by the physical 

 conditions of the ancient areas having remained nearly the same. 

 Let it be remembered that the forms of life, at least those inhabit- 

 ing the sea, have changed almost simultaneously throughout the 

 world, and therefore under the most different climates and con- 

 ditions. Consider the prodigious vicissitudes of climate during 

 the pleistocene period, which includes the whole glacial epoch, 

 and note how little the specific forms of the inhabitants of the sea 

 have been affected. 



On the theory of descent, the full meaning of the fossil remains 

 from closely consecutive formations being closely related, though 

 ranked as distinct species, is obvious. As the accumulation of each 

 formation has often been interrupted, and as long blank intervals 

 have intervened between successive formations, we ought not to 

 expect to find, as I attempted to show in the last chapter, in any 

 one or in any two formations, all the intermediate varieties 

 between the species which appeared at the commencement and 

 close of these periods : but we ought to find after intervals, very 

 long as measured by years, but only moderately long as measured 

 geologically, closely allied forms, or, as they have been called by 

 some authors, representative species ; and these assuredly we do 

 find. We find, in short, such evidence of the slow and scarcely 

 sensible mutations of specific forms, as we have the right to 

 expect. 



On the State of Development of Ancient compared with Living 

 Forms. 



We have seen in the fourth chapter that the degree of differen- 

 tiation and specialisation of the parts in organic beings, when 

 arrived at maturity, is the best standard, as yet suggested, of 

 their degree of perfection or highness. We have also seen that, 

 as the specialisation of parts is an advantage to each being, so 

 natural selection will tend to render the organisation of each 

 \)eing more specialised and perfect, and in this sense higher ; not 

 but that it may leave many creatures with simple and unimproved 

 structures fitted for simple conditions of life, and in some cases 

 will even degrade or simplify the organisation, yet leaving such 

 degraded beings better fitted for their new walks of life. In 

 another and more general manner, new species become superior 

 to their predecessors ; for they have to beat in the struggle for 

 life all the older forms, with which they come into close compe- 

 tition. We may therefore conclude that if under a nearly similar 

 climate the eocene inhabitants of the world could be put into 



