WHAT IS PHYSICAL LIFE 



scent links the whole succession of living 

 forms from the latest back to the earliest, 

 until we cannot but infer that no f onn of 

 earthly life ever came into existence with- 

 out its own living parentage. This de- 

 duction is rendered probable by the fact 

 that the former puzzles of tracing any 

 community of origin between widely sepa- 

 rated living forms existing at present on 

 the earth, is being gradually solved by the 

 discovery of geological records showing 

 that one form after the other formerly ex- 

 isted where their nearest of kin now no 

 longer live. In other words, geology re- 

 cords not only great mutations but also 

 great migrations of both plants and 

 animals. 



But the chief interest of this geological 

 history of earthly life lies in its demonstra- 

 tions of a prolonged and gradual course 

 of development from earlier simpler to 

 later more specialized forms. Now we 



