CONCLUSION 281 



Conclusion 



In the foregoing pages we have attempted to sketch in 

 broad outHnes the course of the origin and evolution of hfe 

 upon the earth in the Hght of our present imperfect knowl- 

 edge, which offers few certainties to guide us and probabilities 

 and possibilities innumerable among which to choose. 



The difference between the non-living world and the living 

 world seems like a vast chasm when we think of a very high 

 organism like man, the result of perhaps a hundred million 

 years of evolution. But the difference between primordial 

 earth, water, and atmosphere and the lowliest known organisms 

 which secure their energy directly from simple chemical com- 

 pounds is not so vast a chasm that we need despair of bridging 

 it some day by solving at least one problem as to the actual 

 nature of life — namely, whether it is solely physicochemical in 

 its energies, or whether it includes a plus energy or element 

 which may have distinguished Life from the beginning. 



The energy conception of the origin and evolution of life, 

 on which are based our fresh stimulus to experiment and re- 

 newed hope of progress in solving the riddle of Heredity, is 

 as yet in its infancy. Our vision will doubtless be amplified 

 by experiment. In seeking the causes of the complex adapta- 

 tions even of the simplest organisms described in Chapters 

 III and IV we soon face the boundaries of the unknown, 

 boundaries which human imagination entirely fails to pene- 

 trate, for Nature never operates as man expects her to, and we 

 believe that imagination itself is strictly limited to recombina- 

 tions of ideas which have come through observation. 



It may be said that the bulk of experimental work hitherto 

 has been in the domain of action and reaction — here lie all the 

 simple energy processes of growth, of waste and repair, of use 



