CHAPTER XXII 



Evolution, Heredity, Eugenics 



Biologists recognize the existence of two factors responsible for 

 the characteristics of living organisms. These are heredity and 

 environment. 



Heredity includes what is handed on from parent to offspring. 

 Sir Ray Lankester says: " Our body cells are merely a husk to pro- 

 tect the germ cells until they are set free to multiply and to start 

 a new individual or husk enclosing in its turn a certain number of 

 cells of the initial germplasm." 



Environment, beginning before birth and continuing until 

 death, includes all physical and chemical forces, acting from without 

 on the germ, embryo, larva, and adult. Profound changes are 

 induced before puberty, and for that matter all through life, as food- 

 stuffs, temperature, oxygen and other factors stimulate or retard 

 the glands of the body regulating growth and metabolism. 



The development of civilization is said to be dependent upon six 

 factors: geographic or climatic conditions, race characteristics, food, 

 social heredity, physical heredity and health. Studies made by the 

 Army and by the United States Public Health Service indicate that 

 not more than fifty per cent of our population are physically fit. 

 It has been demonstrated repeatedly that with improved conditions 

 of health, vice and crime diminish, civilization advances and the 

 whole standard of living improves to the point where past luxuries 

 become the every day equipment of a family. 



Germplasm and Somatoplasm. — For centuries observers have 

 been impressed by the resemblance which children bear to their 

 parents. There seems to be a transmission which is certain but 

 which appears to obey no law, apparently affecting insignificant 

 details and transmitting them with striking fidelity. 



Careful study of the body of an organism shows that there are 

 two kinds of cells, the body cells and the germ cells. The body or 

 somatic cells are those that differentiate to form the tissues of the 

 body. The germ cells are those which are destined to give rise later 

 to an independent organism. Both male and female germ cells 



499 



