516 ZOOLOGY 



John Ray about 1725 crystallized the idea held by Linnaeus 

 and many of his predecessors that organisms arose de novo, by 

 special creation, and since that time have remained practically 

 constant. Cuvier gave this view the support of his influence. 

 Lamarck (17741829) contended that species were changeable, 

 that the fossils in the strata were remains of extinct species 

 which were the ancestors of the present ones. He held that the 

 needs of the organism resulting in the use and disuse of organs, 

 and the action of the environment upon the organism changed 

 individuals and that these modifications were transmitted in 

 some measure to the next generation. Thus he thought evolu- 

 tion occurred. He was the founder of the evolution theory in 

 its modern sense. 



Charles Darwin (1809-1882), accepting essentially La- 

 marck's views, added to them the principle of natural selection 

 (137) through the struggle for existence and the elimination 

 of the unfit. This was his great contribution. It was so rea- 

 sonable and he supported it with such an array of facts that it 

 put the evolution idea on a firm footing and stimulated bio- 

 logical thought and investigation more perhaps than any other 

 suggestion ever proposed. A. R. Wallace shares with Darwin 

 the honor of discovering the idea of natural selection, although 

 the latter 's statement was theoretical rather than experimental. 



With the work of Darwin the idea of the variability of species 

 may be said to become established. The questions now hinged 

 upon the method of origin of the variations and their trans- 

 missibility to new generations. 



August Weismann (1834-1915) held that body characters 

 gained as Lamarck suggested by use and disuse of the body, 

 could not be transmitted to the next generation. Only those 

 changes which take place in the germ plasm could be inherited. 

 He advanced the idea of a continuous germ plasm from which 

 body after body arises in successive generations. Weismann 

 held therefore that Lamarck's supposed factors could have 

 nothing to do with evolution. Their influence stops with the 

 body of the individual. He gave more value to natural selection 

 than even Darwin. 



Gregor Mendel (1822-1884) through his breeding experi- 



