3 io SCIENCE PROGRESS 



The acceptance of this view puts an end to any speculation on 

 the origin of life ; it then simply cannot be discussed at all. 

 On the other hand, the belief is far more prevalent, I think, 

 at least among biologists, that living matter in some form or 

 other arose at some time from that which was not living. In 

 that case there are two further possibilities : first, that life 

 originated on the globe only at some particular period of the 

 earth's history, under special conditions of some kind which 

 do not now exist ; secondly, that the conditions under 

 which life is generated exist always and that new life can be 

 produced in the present or future as well as in the past. 



If life arose from not-living materials at any time on our 

 planet, its origin is a matter not only for discussion but for 

 investigation and experiment. For even if it arose under con- 

 ditions not existing now in Nature, there seems to be no reason 

 why such conditions should not be reproduced artificially. 

 On the other hand, it seems much more reasonable to suppose, 

 as pointed out by the President in his address, that the con- 

 ditions under which life first appeared on the earth were not 

 different from those now existing ; consequently, that if life has 

 arisen once de novo on the earth, it can do so again at any time, 

 past, present or future. 



Why then do we not see new forms of life appearing on the 

 earth ? In the first place, I doubt very much if we are ac- 

 quainted as yet with the simplest forms of life or should be 

 able to recognise them or be aware of their existence at their 

 first appearance. But apart from that, there is another thing 

 to be taken into consideration, as pointed out by Dr. F. J. 

 Allen at the meeting of the British Association in 1896, namely, 

 that if those substances, whatever they may be, which consti- 

 tute the simplest form of living matter or the transitional 

 stage between the living and the not-living were generated 

 now in Nature, they would almost certainly become the prey or 

 the food of some more highly specialised type of existing living 

 being. From this consideration it follows that the evolution of 

 life on the earth could have had only one starting-point. Just as 

 the dominance on the earth at the present time of an intelligent 

 animal, Man, would prevent the evolution of another animal 

 equally intelligent ; so, when once specialised types of living 

 beings had been evolved, a later generation and evolution of 

 life on the earth would have been impossible. In other words, 



