GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 123 



vious. As the accumulation of each formation has often 

 been interrupted, and as long blank intervals have inter- 

 vened 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 com- 

 mencement 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 differentiation and specialization of the parts in organic 

 beings, when arrived at maturity, is the best standard, 

 as yet suggested, of their degree of perfection or high- 

 ness. We have also seen that, as the specialization of 

 parts is an advantage to each being, so natural selection 

 will tend to render the organization of each being more 

 specialized and perfect, and in this sense higher; not but 

 that it may leave many creatures with simple and unim- 

 proved structures fitted for simple conditions of life, and 

 in some cases will even degrade or simplify the organiza- 

 tion, 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 predeces- 

 sors; for they have to beat in the struggle for life all 



