THE APPEARANCE OF LIFE 73 



unaided through the mere action of diverse radiations 

 emanating from the sun or from radio-active bodies, then we 

 can understand how it was that certain of these combinations 

 might have represented the first living substances. 



The question of the first appearance of life returns, then, 

 like the whole subject of physiology, to the domain of physical 

 chemistry. Life arose during conditions which we can now 

 mentally reconstruct, and which still unquestionably persist 

 in some stellar systems, but which have disappeared from the 

 solar system, never to return. The faculty of giving birth to 

 living matter gradually became the province of living beings 

 alone, as the solar radiations and the radio-activity of the earth 

 became feebler, but it has not always been their exclusive 

 privilege. Physical astronomy, disclosing to us the stages 

 of this impoverishment in stars of different ages and of different 

 size, has brought Pasteur's conclusions into harmony with 

 reason, and discredited all those hypotheses — so daring but 

 so contrary to the scientific spirit — of a semination of life on 

 the earth by germs of unknown origin coming from the great 

 Beyond. 



Under what form, then, did the first living organisms 

 manifest themselves ? The earliest fossils we know date from 

 a period so much later than the first appearance of life on earth, 

 and so many forms have disappeared during the metamorphosis 

 of archaic formations that palaeontology cannot aid us in this 

 respect. However, the ties that unite the actual living forms 

 are such that one form can be deduced from the other, on the 

 hypothesis that they are the outcome of a natural evolution, with 

 laws which can be precisely stated. These laws, in turn, permit 

 us to reconstruct with great verisimilitude the different stages 

 through which their various predecessors have passed. After 

 this primary period, palaeontology can provide us with land- 

 marks and the means of checking the inferences we draw from 

 the study of the structure and the embryogenetic development 

 of beings now living, and of the modifications to which they are 

 susceptible. This matter will form the subject of the next 

 chapter. 





