CHAPTER XL 

 HEREDITY AND HUMAN IMPROVEMENT 



Everyone is familiar with the fact that among plants 

 and animals like begets like, or in other words offspring 

 inherit the qualities of their parents. Everyone has 

 noted cases of family resemblance in which certain peculi- 

 arities of form, or facial expression occur in all the children 

 of a family. The peculiar feature known as the Hapsburg 

 lip has characterized for many generations the members 

 of the reigning house of Austria. A white tuft of hair 

 has frequently been transmitted for several generations 

 and there are numerous cases in which supernumerary 

 fingers and toes have likewise been inherited for a long 

 period. These are among the countless illustrations of 

 the operation of heredity. Organisms inherit from both 

 parents apparently to the same degree. And they also 

 inherit qualities from their grandparents and more remote 

 ancestors. Now and then a peculiarity which has long 

 been latent or recessive suddenly crops out and it is then 

 called a case of atavism or reversion. 



The germ cells of organisms are the bearers of hereditary 

 qualities. During development these cells divide and 

 differentiate to form the various parts of the new indi- 

 vidual, but a part of the cells of the embryo give rise to 

 new germ cells, while others produce body or somatic 

 cells. There is an unbroken series of cell generations 

 from the germ cells of the parent to those of the offspring. 

 It has been supposed by many biologists that hereditary 

 resemblance is due to what Weismann has called the con- 



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