SPECULATIONS ON THE ORIGIN OF LIFE 309 



problem are, first, to understand how the complex protein-com- 

 pounds of which living bodies are constituted could have arisen 

 in Nature ; secondly, given the primordial living thing, whatever 

 it was, how it could have maintained its existence on an 

 uninhabited earth — that is to say, what it could have fed on. 

 Both these questions are essentially chemical problems. If 

 living things first originated on the earth, the complex proteins 

 composing the living substance must have been synthesised by 

 some natural process as yet totally unknown ; and the same is 

 true a fortiori if living matter originated off the earth. A 

 terrestrial synthesis of proteins makes the food-problem some- 

 what less difficult, since it may be supposed, as Lankester has 

 suggested, that the primum vivens supported life on the compounds 

 produced as antecedent stages in its own evolution. On the 

 other hand, it is almost painful to think of a minute living 

 creature wafted from infinite space on to an absolutely barren 

 and sterile earth ; the imagination fails to conceive, with such 

 guidance as the present state of knowledge supplies, how it 

 could have got on at all. To obtain light on such questions 

 requires far greater knowledge than we possess at present, not 

 only of the chemistry of the proteins but also of the processes 

 of metabolism and the modes of life of the minuter organisms. 

 It is my conviction that there is a vast field as yet unexplored 

 in this direction and that in the future forms of life will be 

 discovered the very existence of which is as yet unsuspected. 

 Invisible forms of life are now known to exist the discovery of 

 which is due solely to the disturbances caused by them as 

 parasites of ourselves or of other organisms. Is it not then 

 equally possible that other invisible living things exist which, as 

 free-living organisms, produce in their environment effects not 

 as yet perceived by us ? 



Many theories have been put forward at different times with 

 regard to the origin of terrestrial life. 1 Without attempting to 

 give an account of them in any detail, I may summarise briefly 

 the possibilities that have been suggested. In the first place 

 there is the extreme view, represented by Arrhenius, that life 

 has had no origin in finite time but has existed from all eternity 

 and is coeval with matter and energy — that is to say, that in any 

 period of time to which we can throw our thoughts back, 

 matter, energy and life in some form existed in the universe. 

 1 See further my Presidential Address to the Quekett Microscopical Club, 1912 



