THE SPECIES 261 



idea in the forefront of their expositions. Why then this 

 inconsistent avoidance of an evolution of the species ? 



It is because the whole sequence of the various species 

 which palaeontology reveals to us from the Cambrian up to 

 the present day, is regarded by them, not as a life-process, 

 but as explicable by chemical, physical or mechanical causes. 



Variation, according to them, is a chemical process which, 

 without any plan, creates organisms, from among which the 

 struggle for existence exterminates the unfit, i.e. those in- 

 capable of life, so that a selection of the fit is effected. 



The genealogical tree is not meant to give a picture of 

 an inner growth, but merely the result of the influence of 

 external factors. The shape given to the animal kingdom 

 at the present day is the outcome of the action of physical 

 factors on a chemistry that displays no conformity with 

 plan. 



I simply cannot understand how, holding such views, 

 men can talk of an evolutionary idea. For the external 

 factors can at any moment become such that, by extermina- 

 tion of the complex, they make the simple animals the only 

 ones capable of living, and thus bring about a return to the 

 primitive. 



In contrast to the Darwinians, the Lamarckians see at 

 work an internal shaping force, which, in accordance with 

 plan, creates beings that express that plan. The Lamarckians, 

 therefore, may speak of an evolutionary idea. But the signifi- 

 cance they attach to the shaping force is psychological, and 

 so is not controllable by an outside observer. Biology must 

 insist, without qualification, that it shall be so controlled. 



Before examining the scanty facts at our disposal for the 

 comprehension of the evolution of species, I must state the 

 reasons that incline biology to speak of an evolution of species 

 and not of an evolution of individuals. 



I have given detailed reasons for the opinion that, in the 



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