78 A SCIENTIFIC APPROACH 



tremely peculiar conditions which prevailed on the surface of 

 the earth at the time when the first organisms developed. 



Thus Haeckel believed that the most primitive organisms 

 must have arisen spontaneously from inorganic matter as 

 a result of the formative action of some special external 

 physical forces. This does not occur now because those 

 forces which were present on the Earth at an earlier stage 

 in its development have now disappeared and cannot be 

 reproduced. 



Haeckel's contemporary W. Preyer^^ laughed rather malici- 

 ously at these life-forming forces and the conditions which 

 Haeckel supposed to be necessary for the emergence of life 

 in remote geological epochs. He declared that one could 

 not conceive what these conditions might have been. If they 

 were the same as those now prevailing, it would seem that 

 the emergence of life was impossible because, as Pasteur's 

 work showed, this emergence does not occur at present. If 

 the conditions were substantially different the organisms 

 which had emerged would quickly have been destroyed 

 because they only exist at present under very narrowly cir- 

 cumscribed external conditions. 



These ideas of Preyer's seem quite convincing if one adopts 

 a mechanistic position and assumes the sudden emergence 

 of organisms which, though far simpler, already possessed 

 all the organisational characteristics which we find in con- 

 temporary living things. 



Such objections, however, take on a different aspect if we 

 discard mechanistic principles and adopt the point of view 

 that the primaeval living things arose by stages as the result 

 of a prolonged evolution of organic substances, as a particu- 

 lar stage in the general historical development of matter. 

 In this case we shall not need to invent any special forces or 

 conditions. If it had been accomplished by a process of evolu- 

 tion of organic substances, the emergence of the primaeval 

 living things could have occurred under approximately the 

 conditions of temperature, moisture, pressure, illumination, 

 etc., which now prevail on the surface of the Earth. 



There was one condition, necessary for this evolution, 

 which was present then on the surface of the Earth and is 



