16 GENERAL TRIXCIPLES OF ZOOLOGY 



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

 these generalizations led Cuvier to his cataclysm theor}-; that a great 

 revolution brought each period of the earth's history to an end, destroy- 

 ing all life, and that upon the newly formed virgin earth a new organic 

 world of immutable species sprang up. As a believer in the immuta- 

 biHty of species, Cuvier was forced to combat tlie idea of any genetic 

 connection between the li^^ng and the fossil forms. 



Cuvier's theon,- of cataclysms gave no scientilic explanation of the 

 origin of the successive populations of the earth. Such an explanation 

 is only possible by the hypothesis that the later animal worlds have 

 descended from the earlier. So it happened that the idea of the fixity of 

 species was given up and replaced by that of mutability and descent — the 

 theory of 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 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 by 

 Buffon, Geoffroy St. Hilaire, and Lamarck. Its clearest expression was 

 found in Lamarck's "Philosophie zoologique" (1S09); its arguments 

 will be considered in the following paragraphs. 



Lamarck (born, 1744, died, 1S29) taught that at first organisms of 

 the simplest structure arose through spontaneous generation from non- 

 living matter. From these simplest living creatures have developed, by 

 gradual changes in the course of an immeasurably vast space of time, the 

 present species of plants and animals, without any break in the continuity 

 of life upon our globe; the terminal point of this series is man; tlie other 

 animals are the descendants of those forms from which man has developed. 

 Lamarck regarded the animal kingdom as a single series grading from 

 the lowest animal up to man. Among the causes which may influence 

 the change of organisms, Lamarck emphasized particularly use and 

 disuse; the giraffe has obtained a long neck because he was compelled to 

 stretch, in order to browse the leaves on high trees; conversely, the eyes of 

 animals which live in the dark have degenerated from lack of use. The 

 direct influence of the external world must be unimportant; the changes 

 in the surroundings must for the most part act indirectly upon animals by 

 altering the conditions for the use of organs. 



Evolution vs. Creation. — Lamarck's work remained almost unno- 

 ticed by his contemporaries. Later there arose a violent controversy 

 between the defenders and the opponents of the evolution theory when 

 [1830] Geoffroy St. Llilaire in a debate defended against Cuvier the thesis 



