x ELEMENTS OF GENERAL SCIENCE 



PAOR 



CHARTER XXX. THE STRUGGLE FOR EXISTENCE .... 281 



The !iic;iiiiii^ r of tlic term. Overproduction among plants. Over- 

 production among animals. Not food enough for all. Climatic 

 dangers. Destruction by disease. The balance of life. Types of 

 disturbance of nature's balance of life. 



CHAPTER XXXI. PARENT AND OFFSPRING 290 



Which plants and animals are to live. The nature of variation. 

 Hybrids. Natural and artificial selection. Changes in environ- 

 ment. Results of natural selection. Artificial selection. Progres- 

 sive results of artificial selection. The weakness of the artificially 

 selected types. Inheritance. Heredity and the future of the race. 

 Controlling human environment. 



