SOME UNSOLVED SCIENTIFIC PROBLEMS 



of the same matter, subject to the same general laws, 

 and probably passing through kindred stages of evolu- 

 tion and decay, would seem to carry with it the rea- 

 sonable presumption that to all primary planets, such 

 as ours, a similar life-bearing stage must come. But 

 a moment's reflection shows that scientific probabilities 

 do not carry one safely so far as this. Living matter, 

 as we know it, notwithstanding its capacity for varia- 

 tion, is conditioned within very narrow limits as to 

 physical surroundings. Now it is easily to be con- 

 ceived that these peculiar conditions have never been 

 duplicated on any other of all the myriad worlds. If 

 not, then those more complex aggregations of atoms 

 which we must suppose to have been built up in some 

 degree on all cooling globes must be of a character so 

 different from what we term living matter that we 

 should not recognize them as such. Some of them 

 may be infinitely more complex, more diversified in 

 their capacities, more widely responsive to the influ- 

 ences about them, than any living thing on earth, and 

 yet not respond at all to the conditions which we apply 

 as tests of the existence of life. 



This is but another way of saying that the peculiar 

 limitations of specialized aggregations of matter which 

 characterize what we term living matter may be mere 

 incidental details of the evolution of our particular 

 star group, our particular planet even having some 

 such relative magnitude in the cosmic order, as, for ex- 

 ample, the exact detail of outline of some particular 

 leaf of a tree bears to the entire subject of vegetable 

 life. But, on the other hand, it is also conceivable that 

 the conditions on all planets comparable in position to 



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