IMPERFECTION OF GEOLOGICAL RECORD 83 



other; and these links, let them be ever so close, if 

 found in different stages of the same formation, would, 

 by many paleontologists, 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 commence- 

 ment 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 paleontologists — 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 

 Dy this means of a group of forms, all of which are 

 descended from some one progenitor, must have been an 

 3xtremely slow process; and the progenitors must have 

 ived long before their modified descendants. But we 

 ontinually overrate the perfection of the geological 

 'ecord, and falsely infer, because certain genera or 

 'amilies have not been found beneath a certain stage, 

 hat they did not exist before that stage. In all cases 

 «ii)ositive paleontological evidence may be implicitly 

 itirusted; negative evidence is worthless, as experience 

 tijttas so often shown. We continually forget how large 

 i-lhe world is, compared with the area over which our 

 ad geological formations have been carefully examined; we 



