IN THE THEORY OF NATURAL SELECTION. 263 



developmental force ? ' What remains of a whale when we have 

 taken away its adaptive characters ? We are compelled to reply 

 that nothing- remains except the general plan of mammalian 

 organization, which existed previously in the mammalian ancestors 

 of the Cetacea. But if everything which stamps these animals as 

 whales has arisen by adaptation, it follows that the internal de- 

 velopmental force cannot have had any share in the origin of this 

 group. 



And yet this very force is said to be the main factor in the 

 transformation of species, and Nageli unhesitatingly asserts that 

 both the animal and vegetable kingdoms would have become very 

 much as they now are, if there had been no adaptation to new 

 conditions, and no such thing as competition in the struggle for 

 existence l . 



But even if we admit that such an assumption affords some 

 explanation, instead of being the renunciation of all attempts at 

 explanation ; if we admit that an organism, the characteristic 

 peculiarities of which entirely depend upon adaptation, has been 

 formed by an internal developmental force ; we should still be 

 unable to explain how it happens that such an organism, suited to 

 certain conditions of life, and unable to exist under other conditions, 

 appeared at that very place on the earth's surface, and at that very 

 time in the earth's history, which offered the conditions appropriate 

 for its existence. As I have previously argued, the believers in 

 an internal developmental force are compelled to invent an auxiliary 

 hypothesis, a kind of ' pre-established harmony' which explains 

 how it is that changes in the organic world advance step by step, 

 parallel with changes in the crust of the earth and in other 

 conditions of life ; just as, according to Leibnitz, body and soul, 

 although independent of each other, proceed along parallel courses, 

 like two chronometers which keep perfect time. And even this 

 supposition would not be sufficient, because the place must be 

 taken into account as well as the time : thus the whales could not 

 have existed if they had first appeared upon dry land. We know 

 of countless instances in which a species is exclusively and precisely 

 adapted to a certain localized area, and could not thrive anywhere 

 else. We have only to remember the cases of mimicry in which 

 one insect gains protection by resembling another, the cases of 



1 1. c., pp. 117, 286. 



