INTRODUCTION. II 



to answer both questions; or more frequently they 

 assume evolution and attempt simply to find an ex- 

 planation of the fact. 



In the following pages these two questions will 

 be considered separately as far as possible, though 

 they are so intimately connected as to make a com- 

 plete separation impossible. In the first five chap- 

 ters we shall discuss the question whether evolution 

 be a fact. Here we shall consider the various argu- 

 ments which have been adduced to prove that species 

 have been derived from each other, and the various 

 difficulties and objections which have arisen against 

 the unhesitating acceptance of this view. In the 

 sixth and seventh chapters we will examine the sev- 

 eral theories of evolution held by different scientists, 

 which attempt to explain the fundamental fact, and 

 to give the causes which have produced the devel- 

 opment of new species. 



Darwinism proper is, then, not evolution, but its 

 explanation. Darwin's contribution to science was 

 his law of natural selection, a principle which he be- 

 lieved to be the chief cause of the development of 

 new species. Darwin did not originate the theory 

 of evolution, although it is rightly associated with 

 his name. If the writings of Descartes, Leibnitz, 

 and Goethe be carefully studied, the beginnings of 

 the modern ideas involved in the term can be traced. 

 Very indefinite they were, it is true, and so they 

 remained until about the beginning of the present 

 century. At this time a French naturalist, Lamarck, 

 formulated a logical and consistent theory of evolu- 

 tion, a theory which agreed in almost all respects 



