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 
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