in THE MEANING OF EVOLUTION 269 



adopted, or rather invented. Contingent, relative to 

 the obstacles encountered in a given place and at a 

 given moment, is the dissociation of the primordial 

 tendency into such and such complementary tendencies 

 which create divergent lines of evolution. Con 

 tingent the arrests and set-backs ; contingent, in large 

 measure, the adaptations. Two things only are 

 necessary : (i) a gradual accumulation of energy ; (2) 

 an elastic canalization of this energy in variable and in 

 determinable directions, at the end of which are free acts. 

 This twofold result has been obtained in a particular 

 way on our planet. But it might have been obtained 

 by entirely different means. It was not necessary that 

 life should fix its choice mainly upon the carbon of 

 carbonic acid. What was essential for it was to store 

 solar energy ; but, instead of asking the sun to separate, 

 for instance, atoms of oxygen and carbon, it might 

 (theoretically at least, and, apart from practical diffi 

 culties possibly insurmountable) have put forth other 

 chemical elements, which would then have had to be 

 associated or dissociated by entirely different physical 

 means. And if the element characteristic of the sub 

 stances that supply energy to the organism had been 

 other than carbon, the element characteristic of the 

 plastic substances w r ould probably have been other than 

 nitrogen, and the chemistry of living bodies would then 

 have been radically different from what it is. The 

 result would have been living forms without any analogy 

 to those we know, whose anatomy would have been 

 different, whose physiology also would have been differ 

 ent. Alone, the sensori-motor function would have been 

 preserved, if not in its mechanism, at least in its effects. 

 It is therefore probable that life goes on in other planets, 

 in other solar systems also, under forms of which we have 



