Briefly, Darwin's ideas can be stated as the theory of natural 

 selection of the variations which always occur in all species. Be- 

 cause experimental research in physiology and genetics was still 

 undreamed of, he tentatively accepted the Lamarckian theory 

 of the inheritance of acquired characters which come about due 

 to environment and the use and disuse of structures. He ac- 

 counted for this by saying that each cell of the body sends 

 fragments of itself, or "genes", to form the germ cells. When 

 such variations appear, as it is known that they do, whatever 

 their cause, certain ones will be saved; because, (1) far more 

 individuals are born than can survive and reproduce; (2) there 

 is a constant struggle for existence due to shortage of food and 

 space; and (3) there will be a selection by nature, natural 

 selection, of those animals which are most fit for existence. 



Bases of Evidence 



Although evidence for organic evolution has been accumulat- 

 ing since the first observations on natural history were preserved, 

 it was not until Darwin began correlating the facts of different 

 sciences that the evidence was placed upon a sound and co- 

 ordinated basis. Early research in biology was limited to a 

 study of nature, to the naming and cataloguing of specimens. 

 This led to living organisms being grouped into phyla and classes, 

 and the outcome was speculation as to the relationships of 

 genera. From these random speculations and hypotheses grew 

 the theory of evolution, which is now supported by all the 

 biological and geological sciences. 



Arranged in approximate chronological order, the sciences 

 which have contributed to the theory are: (1) Comparative 

 Anatomy; (2) Geographical Distribution, the study of organisms 

 in relation to their distribution on the earth's surface; (3) 

 Palaeontology, the studv of fossils; (4) Embryology; (5) Genet- 

 ics, the study of heredity; and (6) Physiology, the function of 

 cells and tissues. 



The student has studied the theoretical background of evolu- 

 tion in General Biology. The following chapters briefly discuss 

 geographical distribution in relation to the vertebrates; the 

 geological record, and the adaptive radiations of the vertebrates. 



I 



