GENES AND IVIANKESTD — BLIVEN 299 



together. Often such genes appear to have no logical relation to one 

 another, at least in the present state of our understanding. In some 

 families of human beings, for example, a given color of hair is asso- 

 ciated with the lack of one or more of the incisor teeth. By studying 

 family strains it is possible to predict that a child born to certain 

 parents, and having hair of a given color, will possess only six or 

 seven incisors instead of eight. 



This innocent-sounding fact is likely to prove of the very highest 

 practical value to the future of the human race. Many diseases are 

 not predominantly hereditary, but others are, and often you can inherit 

 a predisposition. Among the hereditary ones are some that are par- 

 ticularly terrible in their effects, which nevertheless do not manifest 

 themselves until middle life, after the victim has unwittingly married 

 and had children to whom he can pass on his taint. An example of 

 such a disease is Huntington's chorea, which does not appear until 

 the individual is 35 or 40 years of age. Previously he may have been a 

 fine physical and mental specimen. When Huntington's chorea strikes, 

 he goes to pieces mentally and physically ; his muscles fail ; he sinks 

 into hopeless insanity which usually terminates, after a few years, 

 in death. 



Medical science knows no way to cure this terrible malady; but 

 the knowledge that is coming out of the laboratory gives us the 

 hope of a means by which we could stamp it out in only a few gen- 

 erations. If linked genes could be discovered that are inherited to- 

 gether and transmitted with the disease, latent Huntington's chorea 

 could be identified far in advance through other seemingly harm- 

 less and unrelated characteristics. No civilized person would marry 

 and have children if he knew that such a fate overhung him and 

 them. The time may not be far distant when, thanks to the ad- 

 vance of science, society can say to such an individual long before 

 he reaches the age for fatherhood that it is forbidden to him. Other 

 dread diseases, believed to be hereditary, for which there is now 

 similar hope are muscular atrophy, which brings death at about the 

 age of 20, and hereditary blindness, which may also begin in the 

 late teens. 



Opinion is divided among the experts as to whether it is possible 

 to inherit a predisposition toward diabetes or whether its seeming 

 to "run in families" is due to quite different causes. Whatever 

 the scientific explanation, it is desirable that one who may develop 

 diabetes should be forewarned and should take the necessary steps 

 to safeguard himself by following a hygienic routine of living. 

 Science is now prepared, by the study of family histories, to give 

 warnings of this sort. 



