IN ANY SINGLE FORMATION. 313 



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 sud- 

 denly appear in certain formations, has been urged by sev- 

 eral palaeontologists — for instance, by Agassiz, Pictet, and 

 Sedgwick — as a fatal objection to the belief in the trans- 

 mutation 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 

 progenitor, 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 record, and falsely infer, because certain 

 genera or families have not been found beneath a certain 

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

 positive palseontological evidence may be implicitly trusted ; 

 negative evidence is worthless, as experience has so often 

 shown. We continually forget how large the world is. com- 

 pared with the area over which our geological formations 

 have been carefully examined ; we forget that groups of 

 species may elsewhere have long existed, and have slowly 

 multiplied, before they invaded the ancient archipelagoes of 

 Europe and the United States. We do not make due allow- 

 ance for the intervals of time which have elapsed between 

 our consecutive formations, longer perhaps in many cases 

 than the time required for the accumulation of each forma- 

 tion. These intervals will have given time for the multipli- 

 cation of species from some one parent-form : and in the 

 succeeding formation, such groups or species will appear as 

 if suddenly created. 



I may here recall a remark formerly made, namely, that it 

 might require a long succession of ages to adapt an organism 

 to some new and peculiar line of life, for instance, to fly 

 through the air ; and consequently that the transitional 

 fprms wou!4 pften long remain confined! to some one region, j 



