CHAPTER VI 



THE ORIGIN OF SPECIES [1850]. 



There are three classical works, published at intervals 

 of fifty years, which have exercised a far-reaching 

 influence upon the progress of science and the develop- 

 ment of thought in general. The first of these was 

 Caspar Friedrich WolfF's Theoria Generationis (1759)* i n 

 which the progressive development of the individual by 

 gradual upbuilding (epigenesis) from a simple germ is 

 maintained as against the rival theory (then called 

 "evolution") asserting that this development consists 

 merely in an expansion of parts present from the first. 



Fifty years later (1809) Lamarck published his Philo- 

 sophic Zoologique, in which the progressive development 

 of species (" evolution " in the modern sense) is deduced 

 from various classes of facts, and ascribed to the direct 

 influence of surroundings (environment), of crossing, and 

 of habits (use and disuse). 



After the lapse of still another half-century The 

 Origin of Species by Means of Natural Selection, by Charles 

 Darwin, made its appearance on November 24, 1859, 

 being preceded (July, 1858) by joint communications to 

 the Linnean Society made by the author and Alfred 

 Russel Wallace, who had independently arrived at 

 similar conclusions. The theory of Natural Selection is 

 founded upon three classes of facts, i.e., the keen 

 " struggle for existence " that undoubtedly takes place 

 in nature as the result of rapid increase, the differences 

 between members of the same species (variation), and 



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