The Story of Evolution 111 



survival. The relatively less fit to given conditions will tend to 

 be eliminated, while the relatively more fit will tend to survive. 

 If the variations are hereditary and reappear, perhaps increased 

 in amount, generation after generation, and if the process of 

 sifting continue consistently, the result will be the evolution of 

 the species. The sifting process may be helped by various forms 

 of "isolation" which lessen the range of free intercrossing be- 

 tween members of a species, e.g. by geographical barriers. Inter- 

 breeding of similar forms tends to make a stable stock ; outbreed- 

 ing among dissimilars tends to promote variability. But for an 

 outline like this it is enough to suggest the general method of 

 organic evolution: Throughout the ages organisms have been 

 making tentatives new departures of varying magnitude and 

 these tentatives have been tested. The method is that of testing 

 all things and holding fast that which is good. 



BIBLIOGRAPHY . 



(The following short list may be useful to readers who 

 desire to have further books recommended to them.) 



CLODD, Story of Creation: A Plain Account of Evolution. 



DARWIN, Origin of Species, Descent of Man. 



DEPERET, Transformation of the Animal World (Internal. Sci. Series). 



GEDDES AND THOMSON, Evolution (Home University Library). 



GOODRICH, Evolution (The People's Books). 



HEADLEY, Life and Evolution. 



LULL, Organic Evolution. 



McCABE, A B C of Evolution. 



METCALF, Outline of the Theory of Organic Evolution. 



THOMSON, Darwinism and Human Life. 



WALLACE, Darwinism. 



