the survivors will tend to produce offspring similarly char- 

 acterized." Thus after many generations forms will arise 

 which differ so much from the original forms as to be de- 

 signated new species. The principle of preservation or 

 survival of the fittest Darwin called Natural Selection . 

 Natural Selection "leads to t he improvement of each crea- 

 ture in relation to its organic and inorganic conditions" o f 

 l ileTancl consequently, in most cases, to what must beTe - 

 garded as an advance in organizatio n." (Fig. 2). ' 



^ JJarwm devoted a considerable portion of the ''Origin 

 of Species'' to what he called " Evidences of Organic Evolu- 

 tion." These were considered from the historical stand- 

 point in Chapters X to XIV under the following titles: "On 

 the Imperfection of the Geological Record," "On the Geo- 

 logical Succession of Organic Beings," "Geographical Dis- 

 tribution," "Mutual Affinities of Organic Beings ;"" Mor- 

 phology: Embryology: Rudimentary Organs." Regarding 

 the Imperfection of the Geological Record Darwin claimed 

 that on account of the many gaps in the record of life pre- 

 served in the rocks, it would be hardly possible ever to ex- 

 pect a full knowledge of the organic life that had existed on 

 the earth. Geological evidence, however, as it has accumu- 

 lated since Darwin 's day, is in strong accord with the theory 

 of Evolution. Take for example the history of the ances- 

 tors of the horse in North America, as worked out by 

 Marsh and Osborn, and the Archaeopteryx, the earliest 

 known bird with reptilian characters, etc., etc. Moreover, 

 the geological record shows the gradual appearance of high- 

 er and higher forms. The Invertebrates appeared first, 

 then fis hes, amphibians, reptiles, rnammals and birds i n 

 succession. 



The present distribution of animals and plants over 

 the surface of the earth can be most satisfactorily explained 

 by the theory of evolution. The facts suggest the gradual 

 dispersal of races from a starting point. Many factors, 

 hcjwever, enter into the problem, such as climate and clima- 

 tic changes; oceanic, desert, and mountain barriers; isola- 

 tion, etc. 



/ Darwin found that each island of the Galapagos group 

 had its characteristic animal life, but the species on one 

 island are closely similar to those on another, and to those 

 on the adjoining continent. Moreover, the life on the 

 larger central islands is more closely related than is the life ■ 

 on the more isolated islands. All these facts suggested to 

 Darwin that the corresponding species on the island and 

 the continent are related by a common descent. 



15 



