SOME UNSOLVED SCIENTIFIC PROBLEMS 



tree bears to the entire subject of vegetable life. But, 

 on the other hand, it is also conceivable that the condi- 

 tions on all planets comparable in position to ours, 

 though never absolutely identical, yet pass at some stage 

 through so similar an epoch that on each and every one' 

 of them there is developed something measurably com- 

 parable, in human terms, to what we here know as liv- 

 ing matter; differing widely, perhaps, from any partic- 

 ular form of living being here, yet still conforming 

 broadly to a definition of living things. In that case 

 the life-bearing stage of a planet must be considered as 

 having far more general significance ; perhaps even as 

 constituting the time of fruitage of the cosmic organ- 

 ism, though nothing but human egotism gives warrant to 

 this particular presumption. 



Between these two opposing views every oYie is free 

 to choose according to his preconceptions, for as yet 

 science is unable to give a deciding vote. Equally open 

 to discussion is that other question, as to whether the 

 evolution of universal atoms into a "vital" association 

 occurred but once on our globe, forming the primitive 

 mass from which all the diversified forms evolved, or 

 whether such shifting from the so-called non-vital to the 

 vital was many times repeated perhaps still goes on in- 

 cessantly. It is quite true that the testimony of our 

 century, so far as it goes, is all against the idea of 

 " spontaneous generation " under existing conditions. It 

 has been clearly enough demonstrated that the bacteria 

 and other low forms of familiar life which formerly were 

 supposed to originate "spontaneously" had a quite dif- 

 ferent origin. But the solution of this special case leaves 

 the general problem still far from solved. Who knows 

 what are the conditions necessary to the evolution of the 



451 



