288 GENERAL ZOOLOGY 



he not inherited the ability and the urge to make the most of 

 his opportunities. 



In sharp contrast to cases of inherited mental ability, there are 

 numerous records of marked mental defectiveness, which in the 

 extreme conditions becomes feeble-mindedness or idiocy. The 

 feeble-minded breed feeble-minded. At best they are helpless in 

 competing with normal individuals, and at worst they are 

 depraved and irresponsible. Criminal tendencies of a common 

 sort, often associated with feeble-mindedness, form a prominent 

 feature of the so-called Juke family of New York, whose ancestry 

 has been traced as far back as 1772. In five generations of 1,200 

 individuals, including those who married into it, and who were of 

 the same social stratum, only 20 learned a trade, and of these, 

 10 received their instruction in a state prison. 



Disease. — In order that a disease caused by a microorganism 

 may develop, infection by a specific organism must take place. 

 Such diseases are not inherited. That children of tuberculous 

 parents often develop tuberculosis is due in part to an inherited 

 physiological resistance of a low order, which makes infection 

 more likely than in children of sound healthy parents. A 

 healthy individual may carry the germs of tuberculosis in his 

 mouth, respiratory passages, including the lungs, and yet not 

 develop symptoms of the disease. Disease in parents resulting 

 from infection by pathogenic organisms does not affect their 

 germ cells in such a way as to produce the same disease in their 

 children, in the absence of infection through the usual channels. 

 Theoretically, therefore, and for the most part practically too, 

 it is possible by proper precautions against infection and by 

 providing proper food and living conditions, to rear such chil- 

 dren to healthy adults. 



Syphilis, another disease whose control is important for 

 human society, is also caused by an organism, though the state- 

 ment is frequently heard that it is hereditary. Practically the 

 latter is true, to the extent that the children of syphilitic mothers 

 almost invariably are or become syphilitic. But here again it is 

 not the germ cells that are responsible but the environment, 

 because the opportunities for infection either before, during, or 

 after birth are so great that the offspring rarely escapes. 



Environment. — Attempts to improve the human race by 

 means that fail to take the environment into consideration will 



