ORIGIN OF THE SPECIFIC TYPE 315 



everything that i.s characteristic, that is, typical eitlier of the order or 

 of the family to which animals belong, depends upon adaptation, what 

 room is left for the activity of an internal power of evolution ? How 

 much is left of the whale when the adaptations are subtracted? 

 Nothiiig more than the general scheme of a mammal; but this was 

 miplicit in their ancestors before the whales originated at all. But 

 if what makes whales what they are, that is, the whole ' scheme ' of 

 a Avhale, has originated through adaptation, then the hypothetical 

 evolutionary power— wherever its seat may be— has had no share 

 in the origin of this group of animals. 



I said all this more than ten years ago, but the idea of an 

 internal directive evolutionary force is firmly rooted in many minds, 

 and new modifications of the idea are always cropping up, and of 

 these the most dangerous seem to me to be those which are not clear 

 in themselves, but suppose that the use of a shibboleth like ' organic 

 growth ' means anything. That organic growth is at the base of the 

 phyletic evolution of organisms may be maintained from any scientific 

 standpoint whatsoever, from ours as well as from Nageli's, for no one 

 is so extreme and one-sided as to regard the process of evolution as 

 due solely to internal or tolely to external factors. The process may 

 thus always be compared to the growth of a plant, which likewise 

 depends on both internal a-nd external influences. But that is saying 

 very little ; we have still to show how much and how little is efiected 

 by these internal and external factors, what their nature precisely 

 is, and Avhat relation they bear to one another. There is thus a great 

 difference between believing, with Nageli, that ' the animal and plant 

 knigdoms must have become very much what they actually are, even 

 had there been on the earth no adaptation to new conditions and no 

 competition in the struggle for existence,' and sharply emphasizing, 

 in accordance with the facts just discussed, that, in any case, a Avhole 

 order of mammals — the Cetaceans— could never have arisen at all if 

 there had been no adaptation. 



The same thing could be proved in regard to the class of Birds, for 

 n\ them too we are able to recognize so many adaptive features, that 

 we may say everything about them that makes them birds depends 

 upon adaptation to aerial life, from the articulations of the backbone 

 to the structure of the skull and the existence of a bill; from the 

 transformation of the fore-limbs into wings, and of the hind-limbs to 

 very original organs of locomotion on land or swimming organs in 

 water, to the structure of the bones, the position, size, and number 

 of the internal organs, down even to the microscopic structure of 

 numerous tissues and parts. What could be more characteristic of 



