THE THEORY OF ORGANIC EVOLUTION 161 



and is an illustration of the fact that clues to a rationalistic 

 explanation of human origins were in existence even at this 

 early period. 6 



Naturally enough, these beginnings of evolutionary 

 thought found no supporters during the Middle Ages. Their 

 obliteration was an incident of the decline of Greco-Roman 

 science which has been described in an earlier chapter. 

 Christian theology, through its amplification of the Hebrew 

 story of Creation, furnished an explanation of the origin 

 of man and the universe that was accepted as satisfactory 

 until the Copernican system had displaced the older astron- 

 omy and the sphericity of the earth had become a matter of 

 common knowledge. From the decline of Greek speculative 

 thought until the middle of the eighteenth century, there 

 was no real grappling with the problem of the historical 

 origin of organic beings. Occasionally during the later 

 centuries of this period there were individuals, like Leonardo 

 da Vinci, who recognized the lapse of time involved in 

 geological change and who understood the nature of fossils. 7 

 The Middle Ages stand for the same stagnation here, as in 

 other lines of scientific thought. Only, the concept of 

 organic evolution was longer delayed than any other scien- 

 tific generalization of equal importance. 



Organic evolution appears in its proper setting, if we 

 realize that biological science has but recently passed 

 through a period of battle comparable to that through which 

 astronomical science passed in the period after Copernicus, 

 and geographical science following Columbus. The evolu- 



6 Lucretius, "De Rerum Natura," Book V. Translation by H. J. A. Munro, 

 entitled: "Lucretius on the Nature of Things." 



7 Some of the medieval writings show that fossils were well enough known 

 to demand explanation. For example, these semblances of animal and plant 

 life were said to be caused by "fatty matter set into fermentation by heat"; 

 by "lapidific juice"; by "the tumultuous movement of terrestrial particles." 

 Or they were regarded as: "sports of nature"; as "mineral concretions"; as 

 "creations of plastic force"; as "models," made by the Creator before he 

 decided upon the final forms of creation; or as the bones of animals which had 

 perished in the Noachian deluge. White, A. D., loc. cit. 



