AFFINITIES OF EXTINCT SPECIES. 303 



On the theory of descent, tlie full meanin.fr of the fosHil 

 remains from closely consecutive fonnutions being- closelv 

 related, though ranked as distinct species, is obvious. As 

 the accumulation of each formation has often bfeii inter- 

 rupted, 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 anv 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 lind after 

 intervals, very long as measured by years, but only moder- 

 ately long as measured geologically, closely allied forms, 

 or, as they have been called by some authors, representa- 

 tive 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. 



0^ 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 

 vet suggested, of their degree of perfection or highness. 

 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 tliat 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 organization, 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 liave to 

 beat in the struggle for life all the older forms, with which 

 they come into close competition. We may therefore con- 

 clude that if under a nearly similar climate tiie eocene 

 inhabitants of the world could be put into competition 

 with the existing iidiabitants, the former would be beaten 

 and exterminated by the latter, as would the secondary by 

 the eocene, and the palaeozoic by the secondary forms. iJo 



