256 BIOLOGY: GENERAL AND MEDICAL 



With the coming of the Christian faith speculation 

 upon the ultimate cause of things, their mode of origin 

 and the order of their succession became lost through 

 the acceptance of the Jewish cosmogony which repre- 

 sented the world and all its organized beings as having 

 been created by Yehwe (Jehovah) in the six creation 

 days. 



St. Augustine (A. D. 354-430) entertained a philo- 

 sophical conception of creation that probably grew out 

 of his early Manichean education, and speaks of the 

 "creation of things by a series of causes." Thomas 

 Aquinas (1226-74) recalled St, Augustine's teaching and 

 upheld it, but the "creation" became a dogma of the 

 Church and interrupted scientific thought and investiga- 

 tion for many centuries. 



In tracing the history of the evolutionary hypothesis 

 it is most interesting to observe that it reappeared in the 

 Middle Ages, as it primarily appeared among the Greeks, 

 in the writings of the philosophers and not in those of the 

 naturalists. Thus the German philosopher, Leibnitz, 

 (1646-1716) conceived that living beings form an 

 unbroken series from the simple to the complex, some 

 steps in the series having become extinct. He also 

 conceived that individual forms underwent change as 

 the result of the action of external forces, and believed 

 that Nature was progressive and ever advancing. The 

 advance is, however, slow, hence his dictum, " Natura 

 nonfacit saltum." 



Thoroughly imbued with the teachings of Leibnitz, 

 Buff on (1707-88) continued and enlarged the thought. 

 He believed that organisms could be modified by changes 

 in climate, food, and domestication, and also that parts 

 could be modified by disuse. He also held that all 

 animals might be derived from a single type. 



The philosopher David Hume thought that "the 

 world might have been gradually produced from very 

 small beginnings, increasing by the activity of its in- 

 herent principles rather than by a sudden evolution 



