i 4 GENESIS OF MAN. 



to perceive the manner in which the inheritance of slight variations, 

 however produced, and their transmission to successive generations, 

 brings about, in the course of time, the transformation of some, and 

 the extinction of other species. It is the clear conception and forci- 

 ble presentation of this principle and its happy combination with 

 that of the perpetual competition going on in nature, that gives 

 to Darwin's exposition that air of extreme probability and that 

 power of universal conviction so characteristic of his works. 

 The importance of this distinction between the methods of the 

 two naturalists in expressing this conception may justify me in 

 borrowing a few very appropriate terms from the Biology of Her- 

 bert Spencer for its better illustration. We may then say that 

 while Lamarck seemed clearly to comprehend the influence of the 

 environment [milieu) upon the organism, and to attribute the results 

 to this as the one great and sufficient cause, he failed on the one 

 hand to take in the full scope of the environment, and on the other 

 to conceive of all the susceptibilities of the organism. In his 

 conception of the former he inadequately, if at all, appreciated the 

 organic element, the influence of one organism upon another ob- 

 jectively considered as a modifying force. In his notion of the 

 organism and its susceptibilities he laid too great stress upon the 

 principle of " direct equilibration" and comparatively little upon the 

 far more important one of " indirect equilibration ." To the readers of 

 the Philosophic Zoologique it seemed a crude, to many a ridiculous, 

 explanation of the length of the fore-limbs and neck of the giraffe, 

 that they had become elongated by perpetual attempts to reach 

 the branches of trees that lay beyond the reach of other animals ; 

 and while he admits that this could not have been accomplished 

 by the efforts of any single individual, and ascribes it to a series of 

 cumulative efforts through many generations, thus clearly recog- 

 nizing and expressly affirming the influence of heredity, he yet 

 fails to show the way in which this influence must have been ex- 

 erted, its modus operandi. He does not say, for example, that the 

 great elongation referred to was initiated in some remote ancestor 

 by some slight variation in this direction, either accidental or per- 

 haps due to the animal's efforts ; that this variation, proving ad- 

 vantageous and being transmitted to a numerous progeny, rendered 

 their chances of survival in critical periods greater than those of 

 such as possessed no such peculiarity ; that this power of survival, 



