CHAP. X.] GROUPS OF ALLIED SPECIES. 265 



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 certair 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, compared 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 multi- 

 plied, 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 multiplication 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 forms would often long 

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

 tion 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. Professor Pictet, 

 in his excellent Review of this work, in commenting on early 

 transitional forms, and taking birds as an illustration, cannot see 

 hoAv the successive modifications of the anterior limbs of a sup- 

 posed prototype could possibly have been of any advantage. But 

 look at the penguins of the Southern Ocean ; have not these birds 

 their front limbs in this precise intermediate state of " neither true 

 " arms nor true wings " ? Yet these birds hold their place victori- 

 ously in the battle for life ; for they exist in infinite numbers and 

 of many kinds. I do not suppose that we here see the real 

 transitional grades through which the wings of birds have passed ; 

 but what special difficulty is there in believing that it might profit 

 the modified descendants of the penguin, first to become enabled 

 to flap along the surface of the sea like the logger-headed duck, 

 and ultimately to rise from its surface and glide through the air 1 



I will now give a few examples to illustrate the foregoing, 



