6 THE HYPOTHESIS AND THEORY OF 



on the statement, that the doctrine of evolution 

 as a scientific hypothesis and theory naturally arose 

 from our increased knowledge of zoology, botany, 

 and palaeontology. 



What is then the subject - matter of the 

 doctrine of evolution as a scientific hypothesis 

 and theory ? As I have already suggested, it is 

 primarily to investigate the succession of the forms 

 of plants and animals, since the first appearance 

 of life on our globe, in order to classify species, 

 genera, and families ; and in the second place 

 to explain this order by a natural evolution of species. 

 The object therefore of the science of natural 

 evolution is the investigation, both as to facts and to 

 causes, of the lives of successive organic forms, which 

 terminate in the now existing species. 



And what is not the object of the doctrine of 

 evolution ? It is not its object to explain the origin 

 of life upon this earth. The question whether we 

 must assume spontaneous generation or creation, 

 in order to account for the coming into existence 

 of the first organisms, is a philosophical problem, 

 outside the scope of the scientific theory of evo- 

 lution, and not belonging to it. In my next 

 lecture I intend to discuss these metaphysical 

 problems for to-day I must limit myself to the 

 doctrine of evolution as a scientific hypothesis 

 and theory. 



This doctrine of evolution is obviously not an 

 experimental science ; it is a hypothetical con- 



