4 THE HYPOTHESIS AND THEORY OF 



to connect the heliocentric conception of the uni- 

 verse with the natural evolution of our solar system 

 and the uniform development of the Cosmos as a 

 whole, including all the heavenly bodies. 



In this vast universal evolution, which we assume 

 to have taken place, and which is based on natural 

 laws, the evolution of our little world occupies a 

 scarcely perceptible period of time, barely a minute, 

 and of this minute a small fraction, (that neverthe- 

 less, according to geologists, lasted millions of years), 

 was occupied by the evolution of organic life before 

 the appearance of man. 



The progress made in zoology, botany, and 

 especially in palaeontology has led scientists to 

 investigate more closely the relation existing 

 between our present animals and plants and the 

 extinct fossil varieties. Are we to regard the 

 animal and vegetable kingdoms, as we know them, 

 as something fixed and unchangeable, or are our 

 present animals and plants modified descendants 

 of older, and for the most part extinct, ancestors, 

 which have been to some extent preserved to us 

 as fossils ? 



Two kinds of answers have been given to these 

 questions. The advocates of the theory of per- 

 manence maintain that the systematic species 

 recognised at the present day in our zoological and 

 botanical systems remain unchanged. 1 



1 That the theory of permanence in its historical form assumes the un- 

 changing nature of the systematic genera is well known to every student 



