IN THE THEORY OF NATURAL SELECTION. 295 



natural selection is by no means incompatible with the theory of 

 ' the continuity of the germ-plasm ; ' and, further, that if we 

 accept this latter theory, sexual reproduction appears in an entirely 

 new light : it has received a meaning, and has to a certain extent 

 become intelligible. 



The time in which men believed that science could be advanced 

 by the mere collection of facts has long passed away: we know 

 that it is not necessary to accumulate a vast number of miscel- 

 laneous facts, or to make as it were a catalogue of them ; but we 

 know that it is necessary to establish facts which, when grouped 

 together in the light of a theory, will enable us to acquire a certain 

 degree of insight into some natural phenomenon. In order to 

 direct our attention to those new facts which are of immediate 

 importance, it is absolutely necessary to seek the aid of some 

 general theory for the arrangement and grouping of those which 

 we already possess. This has been my object in the present paper. 



But it may be perhaps objected that these phenomena are far too 

 complicated to be attacked at the present time, and that we ought 

 to wait quietly until the simpler phenomena have been resolved into 

 their components. It may be asked whether the trouble and 

 labour involved in the attempt to solve such questions as heredity 

 or the transformation of species are not likely to be wasted and 

 useless. 



It is true that we sometimes meet with such opinions, but I 

 believe that they are based upon a misunderstanding of the method 

 which mankind has always followed in the investigation of nature, 

 and which must therefore be founded upon the necessary relations 

 existing between mankind and nature. 



Science has often been compared to an edifice which has been 

 solidly built by laying stone upon stone, until it has gradually 

 risen to greater height and perfection. This comparison holds 

 good up to a certain point, but it leads us to easily overlook the 

 fact that this metaphorical building does not at any point rest 

 upon the ground, and that, at least up to the present time, it has 

 remained floating in the air. Not a single branch of science, not 

 even Physics itself, has commenced building from below; all 

 branches have begun to build at greater or less heights in the air, 

 and have then built downwards: and even Physics has not yet 

 reached the ground, for it is still very uncertain as to the nature of 



