I06 THE EVOLUTION OF MAN. 



Archseology. However much particular items of such induc- 

 tive knowledge may in time be improved and modified, 

 their general significance, as a whole, remains quite un- 

 touched. 



The Theory of Descent, according to Lamarck and Dar- 

 win, as a great inductive law, and indeed the greatest of 

 all inductive biological laws, is in the first place based on the 

 facts of Paltfiontology, on the modification of species brought 

 to light by the science of Petrifactions. From the condi- 

 tions under which these fossils, or petrifactions, are found 

 buried in the rock-layers of our earth, we draw the first 

 sure conclusion, that the organic population of the earth, as 

 well as the crust of the earth itself, has been slowly and 

 gradually evolved, and that series of diverse populations 

 have successively appeared at different periods of the 

 earth's history. Modern geology shows us that the evolu- 

 tion of the earth has been gradual, and without total and 

 violent revolutions. Comparing the various plant and 

 animal creations that have successively appeared during the 

 course of the earth's history, we find, in the first place, that 

 an increase in the number of species has been constant and 

 gradual from the earliest to the most recent times ; and, in 

 the second place, we pei'ceive that the increase in the per- 

 fection of the forms belonging to each of the larger groups 

 of animals and plants is also constant. For example, the 

 only Vertebrates existing in the earliest times are the lower 

 Fishes ; then the higher kinds of Fishes ; later Amphibia 

 appear; still later, the three higher classes of Vertebrates, 

 Reptiles first, then Birds, and Mammals ; of these only the 

 most imperfect and lowest forms appear first ; it is only at 

 a very late period that the higher placental Mammals 



