288 THE ORIGIN OF SPECIES 



transitional links between the species which lived at the com- 

 mencement and close of each fonnation, 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 palaeon- 

 tologists — 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 develop- 

 ment by this means of a group of forms, all of which are de- 

 scended 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 per- 

 fection 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 

 palaeontological evidence may be implicitly trusted; negative evi- 

 dence is worthless, as experience has so often shown. We con- 

 tinually forget how large the world is, compared with the area 

 over which our geological formations have been carefully exam- 

 ined; 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 allowance 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 

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

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

 ing 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 forms would often 

 long remain confined to some one region; but that, when this 

 adaptation had once been effected, and a few species had thus 

 acquired a great advantage over other organisms, a comparatively 

 short time would be necessary to produce many divergent forms, 

 which would spread rapidly and widely throughout the world. 



