The Story of Evolution 



61 



the earth. No one knows how, but it is interesting to consider 

 possibilities. 



From ancient times it has been a favourite answer that the 

 dust of the earth may have become living in a way which is out- 

 side scientific description. This answer forecloses the ques- 

 tion, and it is far too soon to do that. Science must often 

 say "Ignoramus": Science should be slow to say "Ignora- 

 bimus." 



A second position held by Helmholtz, Lord Kelvin, and 

 others, suggests that minute living creatures may have come to 

 the earth from elsewhere, in the cracks of a meteorite or among 

 cosmic dust. It must be remembered that seeds can survive 

 prolonged exposure to very low temperatures; that spores of 

 bacteria can survive high temperature; that seeds of plants and 

 germs of animals in a state of "latent life" can survive prolonged 

 drought and absence of oxygen. It is possible, according to 

 Berthelot, that as long as there is not molecular disintegration 

 vital activities may be suspended for a time, and may afterwards 

 recommence when appropriate conditions are restored. There- 

 fore, one should be slow to say that a long journey through space 

 is impossible. The obvious limitation of Lord Kelvin's theory 

 is that it only shifts the problem of the origin of organisms (i.e. 

 living creatures) from the earth to elsewhere. 



The third answer is that living creatures of a very simple 

 sort may have emerged on the earth's surface from not-living 

 material, e.g. from some semi-fluid carbon compounds activated 

 by ferments. The tenability of this view is suggested by the 

 achievements of the synthetic chemists, who are able artificially 

 to build up substances such as oxalic acid, indigo, salicylic acid, 

 caffeine, and grape-sugar. We do not know, indeed, what in 

 Nature's laboratory would take the place of the clever synthetic 

 chemist, but there seems to be a tendency to complexity. Corpus- 

 cles form atoms, atoms form molecules, small molecules large 

 ones. 



