The Evolution of Organisms 137 



been taken for granted, and there has been a con- 

 centration of inquiry on the originative and di- 

 rective factors in the mysterious process of organic 

 becoming. 1 



Stated concretely, the general doctrine of de- 

 scent or organic evolution suggests, as we all know, 

 that the plants and animals now around us are the 

 results of natural processes working throughout 

 the ages, that the forms we see are the lineal de- 

 scendants of ancestors on the whole somewhat 

 simpler, that these are descended from yet simpler 

 forms, and so on backward, till we lose our clue 

 in the unknown but doubtless momentous vital 

 events of pre-Cambrian ages, or, in other words, 

 in the thick mist of life's beginnings. 



Why do we accept this modal interpretation? 

 The view that things have always been as they are 

 is demonstrably false; the theory of successive 

 cataclysms and subsequent recommencements is 

 hardly thinkable; the only available scientific 

 formulation is the theory of descent. We accept 

 it because it fits the facts we know, because no 

 facts contradict it, because it is congruent with our 

 interpretation of other orders of facts. We can- 

 not verify it as we can verify the indestructibility 

 of matter, the conservation of energy, or the for- 

 mula of gravitation, but we do know that there is a 



1 See the author's " Study of Animal Life " and " The 

 Science of Life." 



