Chap.X.] in any single POEMATION. 77 



geological sections, had not the absence of innumerable 

 transitional links between the species which lived at 

 the commencement and close of each formation, pressed 

 60 hardly on my theory. 



On the sudden Appearance of whole Groups of allied 

 Species. 



The abrupt manner in which whole groups of spe- 

 cies suddenly appear in certain formations, has been 

 urged by several palaeontologists — ^for instance, by Agas- 

 siz, Pictet, and Sedgwick — as a fatal objection to the be- 

 lief in the transmutation of species. If numerous spe- 

 cies, 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 progenitor, must 

 have been an extremely slow process; and the progeni- 

 tors must have lived long before their modified descen- 

 dants. But we continually overrate the perfection of 

 the geological record, and falsely infer, because certain 

 genera or families have not been found beneath a cer- 

 tain stage, that they did not exist before that stage. 

 In all cases positive palaeontological 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 



