2B2 SUDDEN APPEARANCE OF [Chap. X. 



their ancient homes, as they would differ from their former state 

 in a nearly uniform, though perhaps extremely slight degree, and 

 as they would be found embedded in slightly different sub-stages of 

 the same formation, they would, according to the principles followed 

 by many palaeontologists, be ranked as new and distinct species. 



If then there be some degree of truth in these remarks, we have 

 no right to expect to find, in our geological formations, an infinite 

 number of those fine transitional forms which, on our theory, have 

 connected all the past and present species of the same group into 

 one long and branching chain of life. We ought only to look for a 

 few links, and such assuredly we do find — some more distantly, 

 some more closely, related to each other ; and these links, let them 

 be ever so close, if found in different stages of the same formation, 

 would, by many palaeontologists, be ranked as distinct species. 

 But I do not pretend that I should ever have suspected how poor 

 was the record in the best preserved geological sections, had not the 

 absence of innumerable transitional links between the species which 

 lived at the commencement and close of each formation, pressed so 

 hardly on my theory. 



On the sudden Appearance of whole Groups of allied Species. 



The abrupt manner in which whole groups of species suddenly 

 appear in certain formations, has been urged by several palaeontolo- 

 gists — for instance, by Agassiz, Pictet, and Sedgwick— as a fatal 

 objection to the belief in the transmutation of species. If numerous 

 species, belonging to the same genera or families, have really started 

 into life at once, the fact would be fatal to the theory of evolution 

 through natural selection. For the development by this means of 

 a group of forms, all of which are descended from some one progeni- 

 tor, must have been an extremely slow process; and the progenitors 

 must have lived long before their modified descendants. But we 

 continually overrate the perfection of the geological recDrd, and 

 falsely infer, because certain genera or families have not been found 

 beneath a certain stage, that they did not exist before that stago. 

 In ail cases positive pakeontological evidence may be implicitly 

 trusted ; negative evidence is worthless, as experience has so often 

 shown. "We continually forget how large the world is, compared 

 with the area over which our geological formations have been 

 carefully examined; we forget that groups of species may else- 

 where have long existed, and have slowly multiplied, before 

 they invaded the ancient archipelagoes of Europe and the United 

 States. We do not make due allowance for the intervals of 

 time which have elapsed between our consecutive formations, — 



