DARWINISM 513 



3. Fitness for Environment. — It is common knowledge 

 that living things must be adjusted to their environment. 

 Poor adjustment means sickness or weakness; complete 

 or nearly complete lack of adjustment means death. 

 Water-lilies, for example, cannot live in the desert, 

 cacti cannot live in salt marshes; cocoanuts cannot be 

 grown except in subtropical or tropical climates, edelweiss 

 will not grow in the tropics. This is because these various 

 kinds of plants are so organized that they cannot adjust 

 themselves to external conditions, beyond certain more or 

 less definite limits or extremes. A cactus is fit to live in 

 the desert because it is protected by its structure against 

 excessive loss of water, and has special provision for 

 storing up water that may be used in time of drought. 

 Deciduous trees are fitted to live in temperate regions, 

 partly because their deciduous habit, and their formation 

 of scaly buds enables them to withstand the drought of 

 winter. Negroes live without discomfort under the trop- 

 ical sun because they are protected by the black pigment 

 in their skin. And so, in countless ways, we might illus- 

 trate the fact that all living things, in order to flourish, 

 must be adjusted to their surroundings. 



4. Struggle for Existence. — The clue to the method of 

 evolution first dawned upon Darwin in 1838, while reading 

 Malthus on "Population." Malthus emphasized the fact 

 that the number of human beings in the world increased 

 in geometrical ratio (by multiplication) , while the food sup- 

 ply increased much less rapidly by arithmetical ratio (by 

 addition). Therefore, argued Malthus, the time will soon 

 be reached when there will not be food enough for all; 

 men will then struggle for actual existence, and only the 

 fittest (i.e., the strongest, the fleetest, the most clever or 



