ORIGIN OF SPECIES 241 



Reproduction then became a reduplication that 

 faithfully copied the parent form, the succeeding 

 generations showing only such variations as attend 

 the transmission of hereditary traits from two 

 parents. Cross breeding, when possible, generally 

 resulted in sterile offspring. The form was fixed. 

 (See p. 138.) As a fixed form of this kind I describe a 

 species. And thus the theory accounts for the fixity, 

 the specificity, of the species of geologic times which, 

 Osborn and Loeb have said, persisted for "from two 

 to possibly two hundred millions of years." {See 

 p. 207.) 



One can conceive the possibility or probability 

 of one incipient form, if sufficiently complex, giving 

 rise to a variety of forms that ultimately resulted in 

 separate species. Also some forms would remain less 

 rigid than others, and these might produce a series 

 in which the successive generations developed specific 

 characteristics; or these less rigid forms through 

 interbreeding would result in slight or pronounced 

 variations. There is the famous example of the 

 evolution of the horse, described by Henry Fairfield 

 Osborn, ^^ the other of the Formenreihe of Waagen; 



" The Origin and Evolution of Life, 266-269; "Recent Advances in our 

 Knowledge of the Horse," Proceedings of the American Philosophical Society, 

 XLIII (April, 1904), 156; "The Evolution of the Horse," Report British Associ- 

 ation for the Advancement of Science, 1905, pages 607 and 608; "The Continuous 

 Origin of Certain Unit Characters as Observed by a Paleontologist," Harvey 

 Society Volume, seventh series, November, 1912, pages 153-204. 



