CH. XT.I. NA TURAL SELECTION. 471 



different sciences standing each alone, which the great men 

 of earlier centuries worked out, we are beginning to be able 

 to discern one constant power working through them all ; 

 while still new fields of discovery, such as that which spec- 

 trum analysis has only lately opened out to us, help us to 

 bear in mind how little we know, and how much more vast 

 than anything that we can imagine must be the great 

 scheme of Creation which is being worked out around and 

 within us. 



But even if future study should lead biologists to modify 

 in some ways Darwin's theory of the origin of species, the 

 impulse which it has given to the study of plants and 

 animals cannot be over-estimated. Fifty years ago the 

 naturalist might, and did, find great interest in discovering 

 new species of animals and plants, and studying their habits 

 and nature ; while the anatomist and physiologist classified 

 forms according to their structure, and thus we were 

 beginning to arrive at a fair general view of the plant and 

 animal kingdoms. Here, however, the interest ended ; for 

 there was then no idea that the structure, nature, and habits 

 of living beings could help us to unravel the history of past 

 life upon the globe ; nor that every hair, and bone, and tint 

 of colour is a clue to the working of general laws by which 

 the various forms have 'arisen and filled the earth. This 

 conception was only possible after Darwin had shown in 

 his 'Origin of Species' (see p. 464) that 'the structure of each 

 part of each species, for whatever purpose used, will be the 

 sum of the many inherited changes through which that 

 species has passed during its successive adaptations to 

 changed habits. and conditions of life.' 



Now, see what a field this opens to the most humble 

 student of nature, if he only work conscientiously. For 

 nierly, a plant or animal stood alone, and the question, how 



