24 Causes of its Success 



which revealed one of the great unifying principles 

 of the cosmic order. 



Darwin had found one of the great secrets at 

 the heart of the evolutionary process for which a 

 long line of investigators from the days of Aristotle 

 had sought in vain, — the thin red line which was 

 to guide him, and after him all workers in the 

 natural sciences, through the labyrinth of the 

 infinite variety of the facts of Nature. The work 

 undoubtedly marks one of the most important 

 events in the history of the human race. Not 

 only was it epoch-making because with its publica- 

 tion Nature re-entered upon a grand and magnifi- 

 cent unity. It was important, too, because it 

 marked the enfranchisement of the human spirit 

 from a mediaeval theology, from outworn tradi- 

 tions, from ancient routines, atid the ignorance and 

 superstitions of a barbarous past. Man raised his 

 head; he felt himself master of the world; he saw 

 infinite horizons opening before his eyes, with no 

 authority which henceforth could arrest him in his 

 conquest. We can understand with what enthu- 

 siasm this definite liberation of the human mind 

 would be received by the thinkers of a purely 

 scientific spirit. 



It would be difficult to exaggerate the changes 

 which have come about in all departments of 

 human thought, as the result of the theory of 

 natural selection. During the past half century, 

 all the sciences, from astronomy to sociology, have 

 been profoundly influenced by Darwin's discovery 



