CHAPTER XXX 

 PRACTICAL LAWS OF LIFE 



GEOMETRICAL INCREASE AND STRUGGLE FOR LIFE. VARI- 

 ATION. SELECTION AND SURVIVAL OF THE FITTEST. 

 HEREDITY. GENETICS. EUGENICS 



It is good thus to try in imagination to give to any one species an advan- 

 tage over another. Probably in no single instance should we know what 

 to do. This ought to convince us of our ignorance on the mutual relations 

 of all organic beings ; a conviction as necessary as it is difficult to acquire. 

 All that we can do is to keep steadily in mind that each organic being 

 is striving to increase in a geometrical ratio ; that each at some period 

 of life, during some season of the year, during each generation or at inter- 

 vals, has to struggle for life and to suffer great destruction. When we 

 reflect on this struggle, we may console ourselves with the full belief, that 

 the war of nature is not incessant, that no fear is felt, that death is gener- 

 ally prompt, and that the vigorous, the healthy, and the happy survive and 

 multiply. CHARLES DARWIN, " Origin of Species, 1 ' p. 96 



An exact determination of the laws of heredity will probably work more 

 change in man's outlook on the world and in his power over nature than 

 any other advance in natural knowledge that can be clearly foreseen. 

 BATESON, "Mendel's Principles of Heredity," 1902, p. 1 



To unravel the golden threads of inheritance which have bound us all 

 together in the past, as well as to learn how to weave upon the loom of the 

 future not only those old patterns in plants and animals and men which 

 have already proven worth while, but also to create new organic designs of 

 an excellence hitherto impossible or undreamed of, is the inspiring task 

 before the geneticist to-day. WALTER, "Genetics," p. 5 



It is as impossible now to take the ideas of descent and of natural selec- 

 tion out of the world as to take a star out of the sky. CRAMER, " Method 

 of Darwin," p. 61 



Mankind is slowly discovering the laws of life. Ignorance 

 cannot, in the nature of the case, bring exemption from the 

 consequences' of breaking laws ; hence failure even to try to 



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