384 ORIGIN OF SPECIES 



alone, from. its generality, seems to have shaken Professor 

 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 resem- 

 blance of distinct species in closely consecutive formations, 

 by the physical conditions of the ancient areas having re- 

 mained nearly the same. Let it be remembered that the 

 forms of life, at least those inhabiting the sea, have changed 

 almost simultaneously throughout the world, and therefore 

 'under the most different climates and conditions. 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 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 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 

 differentiation 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 ad- 

 vantage to each being, so natural selection will tend to render 



