THE PERIOD OF INCUBATION 63 



for taking trouble. For five years, as a mere pre- 

 liminary, he accumulated facts in immense variety, and 

 then for the first time and in the vaguest possible way 

 he ' allowed himself to speculate/ That brings us down 

 to the year 1842, when the first notes of the ' Origin of 

 Species' must have been tentatively committed to 

 paper. "It was in 1859 that the first edition of the 

 complete work was given to the world. Compare this 

 with the case of Newton, who similarly kept his grand 

 idea of gravitation for many years in embryo, until 

 more exact measurements of the moon's mass and dis- 

 tance should enable him to verify it to his own satis- 

 faction. 



One other item of immense importance in the genesis 

 of the full Darwinian doctrine deserves mention here 

 I mean, the exact moment of time occupied by Charles 

 Darwin in the continuous history of scientific thought. 

 A generation or two earlier, in Erasmus Darwin's days, 

 biology had not yet arrived at the true classification of 

 animals and plants upon an essentially hereditary basis. 

 The Linnasan arrangement, then universally accepted, 

 was wholly artificial in its main features ; it distributed 

 species without regard to their fundamental likenesses 

 of structure and organisation. But the natural system 

 of Jussieu and De Candolle, by arranging plants into 

 truly related groups, made possible the proofs of an 

 order of affiliation in the vegetable kingdom; while 

 Cuvier's similar reconstruction of the animal world 

 gave a like foothold to the evolutionary philosopher in 

 the other great department of organic nature. The 

 recognition of kinship between the various members 

 of the same family necessarily preceded the establish- 



