566 EVOLUTION 



an epidermis that affords very little protection against excessive 

 transpiration, they will likely perish during drought. The 

 advantage certain individuals have over others may be due to a 

 variation in rate of growth. The individuals with the most 

 rapid rate of growth get ahead and crowd out the slower growing 

 individuals. Individuals may be better or not so well equipped 

 for the struggle due to variations in number of seeds produced, 

 in ways of disseminating the seeds, in ability to endure low 

 temperatures and resist the attacks of disease producing organism, 

 etc. Plants and animals vary in all directions and in all degrees 

 of magnitude, and consequently the individuals of a group of 

 plants or animals are variously adapted to compete in the struggle 

 for existence. Only a few out of the many individuals are for- 

 tunate enough to vary in such a way as to be well adjusted to 

 their surroundings and thus well equipped for the struggle. 

 Thus as a result of variations, individuals are variously adapted 

 to their surroundings and natural selection is thereby afforded an 

 opportunity to work. 



Struggle for existence. — It is in the struggle for existence that 

 the fitness or unfitness of individuals to live is determined. 

 Individuals survive or perish according to whether they win or 

 lose in the struggle for space, light, food, moisture, etc., with the 

 other individuals with which they are associated. 



Of the numerous individuals that come into the world only a 

 few live out their life cycle. There isn't space and food enough 

 for more than a few of the many individuals that come into the 

 world. But each individual asserts its right to live and hence 

 the struggle which results in the destruction of many and the 

 survival of the few. Plants struggle with each other for space, 

 moisture, food, light, etc. They have to struggle against the 

 attacks of disease producing organisms and against the attacks 

 of insects and larger animals. Hail, winds, intense heat and 

 other unfavorable weather conditions play a part in the destruc- 

 tion of both plants and animals. With the cultivator and hoe we 

 help our useful plants to win in the struggle with wee ds. In most 

 any group of plants one can see the struggle go on. Some plants 

 soon over-top the others which sooner or later perish for lack of 

 space, light, food, and moisture. In all stages of development, 

 from the seed stage to the seed-bearing stage, the unfortunate 

 individuals succumb in the struggle. Many plants are destroyed 



