HISTORY OF ZOOLOGY. 21 



seiniiialis, a fertilizing breath, which, if it fell upon organic bodies, 

 led to the formation of animals and plants, but if it strayed upon 

 inorganic materials gave rise to fossils. The foundation of 

 scientific paleontology by Cuvier put an end to such empty specu- 

 lations. Cuvier proved beyond a doubt that these fossils were the 

 remains of animals of a previous time. Just as the formation of 

 the earth's crust by successive overlying layers made possible the 

 recognition of different periods in the earth's history, so paleon- 

 tology taught how to recognize also the different periods in the 

 vegetable and animal world of life on our globe. Each geological 

 age was characterized by a special world of animals quite peculiar 

 to it; and these animal worlds differed the more from the present, 

 the older the period of the earth to which they belonged. All 

 these generalizations led Cuvier to his cataclysm theory, that a 

 great revolution brought each period of the earth's history to an 

 end, destroying all life, and that upon the newly formed virgin 

 earth a new organic world of immutable species sprang up. 



Objections to the Cataclysm Theory. By the supposition of 

 numerous acts of creation the Linnean conception of species 

 seemed to be rescued, though, to be sure, by summoning to its aid 

 hypotheses which had neither foundation in science nor justifica- 

 tion in theology. The logical results of Cuvier's cataclysm theory 

 were conceptions of a Creator who built up an animal world only 

 for the purpose of destroying it after a time as a troublesome toy; 

 it has therefore at no time found warm supporters, at least among 

 geologists, for whom it was intended. Of the prominent zoologists 

 there is only to be mentioned Louis Agassiz, who till the end of 

 his life remained faithful to this theory. 



Under these conditions it is readily understood how thinking 

 naturalists, who felt the necessity of explaining the character of 

 organic nature simply and by a natural law capable of general 

 application, began to doubt the fixity of species, and were led to 

 the theory of change of form, the Theory of Descent, or Evolution. 



Darwin's Predecessors. Even in Cuvier's time there prevailed 

 a strong current in favor of this theory. It found expression in 

 England in the writings of Erasmus Darwin (grandfather of the 

 renowned Charles Darwin); in Germany in the works of Goethe, 

 Oken, and the disciples of the ' natural philosophical' school; in 

 France the genealogical theory was developed particularly by 

 Buffon, Geoffroy St. Hilaire, and Lamarck. Its completest ex- 

 pression was found in Lamarck's " Philosophic zoologique " (1809) ; 

 its arguments will be considered in the following paragraphs. 



