9 8 EVOLUTION OF THE EARTH 



waves from the sun of the nearest solar system, it would re- 

 quire many thousand years to reach the earth. Only on the 

 view that cells are potentially immortal and can remain in a 

 dormant condition nearly indefinitely can we believe that life 

 has reached the earth from other planets. Arrhenius maintains 

 that this is possible owing to the exceedingly low temperature 

 and absence of water-vapor which must prevail in cosmic space ; 

 and Loeb states that there is no reason why spores should lose 

 appreciably more of their germinating power in ten thousand 

 years than in six months. 14 



Without further discussion it is apparent that the theory is 

 one which cannot be proved or disproved. At first thought, 

 and as first outlined by Richter, it commanded little serious 

 attention; but with its strictly scientific formulation by later 

 physicists and biologists, and especially in view of our increas- 

 ing appreciation of the potentialities of life in the latent state, 

 we are justified perhaps in seriously questioning, with Helm- 

 holtz, "whether after all life has ever arisen, whether it may 

 not be even as old as matter, and whether its germs, passing 

 from one world to another, may not have developed where 

 they found favorable soil." But the majority of biologists un- 

 doubtedly would agree with Schafer that, "knowing what we 

 know, and believing what we believe, as to the part played by 

 evolution in the development of terrestrial matter, we are, 

 without denying the possibility of the existence of life in other 

 parts of the universe, justified in regarding these cosmic theories 

 as inherently improbable at least in comparison with the solu- 

 tion of the problem which the evolutionary hypothesis offers." 15 



14 Arrhenius, S., "Worlds in the Making." English translation by H. Borns, 



1908. 

 Loeb, J., "The Organism as a Whole from a Physicochemical Viewpoint," 



1916. 

 Woodruff, L. L., "A Pedigreed Race of Paramecium." Proc. Soc. Exp. Biol. 



and Med., vol. 9, 1912. 



15 Schafer, E. A., "Life: Its Nature, Origin and Maintenance." Presidential 

 address, Brit. Assoc. Adv. Sci. Science, new ser., vol. 36, 1912, pp. 289-312. 



