236 



LIFE ON THE EARTH 



lie Health Service and many private agencies are at 

 work helping to make better living conditions for all 

 people. 



What is your community doing to provide better 

 living conditions for its citizens? 



The achievements of people are not transmitted to 

 their offspring by heredity. We are not born with the 

 ability to read, write, do arithmetic problems, or speak 

 English. Each person must learn to do these things by 

 application and hard work. In other words, education 

 must begin all over again with each generation. For 

 this reason, schools will probably always be the most 

 important of all our social institutions. Schools help 

 us to become intelligent citizens. 



Every trait or characteristic an individual possesses 

 is either inherited or acquired. For a long time it was 

 thought that the traits we acquire during a lifetime 

 affect the next generation. We now know that ac- 

 quired characteristics are not inherited. Acquired 

 characteristics affect only the persons who have ac- 

 quired them. 



Germ diseases are 

 not inherited. Germs 

 are tiny microscopic 

 plants or animals pres- 

 ent in our environment. 

 To become afflicted 

 with a germ disease a 

 person must first come 

 into contact with the 

 germ which causes the 

 disease. However, a 

 person may be born 

 with a poor resistance 

 to certain germ dis- 

 eases. This is believed 

 to be true for tubercu- 

 losis and cancer. Cer- 

 tain families seem to 

 possess less resistance 

 to these diseases than 

 other families. Some or- 

 ganic diseases, that is, 



diseases not caused by germs, such as diabetes, St. 

 Vitus's dance, and pernicious anemia, and the tend- 

 ency toward bronchial asthma, certain forms of 

 rheumatism, gout, and goitre may also be inherited. 



Feeble-mindedness, epilepsy, and certain forms of 

 insanity are inherited. There are a number of different 

 kinds of insanity ; how many has not yet been deter- 

 mined. Some forms are acquired ; others are inherited. 

 Possibly as many as fifty per cent of the cases of in- 

 sanity are directly or indirectly due to heredity. 



Deafness and blindness may be either acquired or 

 inherited. 



U. S. Deft, of Agriculture 



FlG. 375. OUR DOMESTIC PIGS 



HAVE BEEN DEVELOPED FROM A 



SMALL WILD FORM 



Have animals been improved by man? The im- 

 provement of plants and animals is made possible 

 because of our knowledge of heredity and variation. 

 Sometime during the development of our civilization 

 man began the domestication of horses, cattle, sheep, 

 and other animals. The strongest and best of the 



SCOTCH TERRIER 



FRENCH POODLE 



COLUE 



WOLF 



GREYHOUND 



ST. BERNARD 



.* 



ENGLISH SETTER 



FIG. 376. ALL OUR DOMESTICATED DOGS MAY HAVE 

 DESCENDED FROM THE WOLF 



young were raised for breeding purposes, and in this 

 way man aided nature in producing better stock. All 

 our domesticated dogs are descended from the wolf, 

 but the continual breeding for certain desired traits 

 has resulted in many varieties. Man has changed the 

 horse by breeding for desired characteristics so that 

 today we have race horses, trotters, draft horses, and 

 coach horses. In a similar manner all of our domesti- 

 cated animals have been tremendously changed by 

 controlled breeding since they were first captured in 

 the wild state. Today every successful farmer knows 

 that the best results are obtained only from good stock 

 and that to produce the best it is necessary to breed 

 from the best. 



It is not unusual for thousands of dollars to be 

 paid for cows with exceptional records and good an- 

 cestry. Certain championship cattle have sold for 

 more than $50,000. There is, however, much poor 

 stock in this country. "Good judges believe that in the 

 entire country one fourth of the cows kept for milk 

 do not pay for their cost of keeping, and nearly a 

 fourth more fail to yield an annual profit. As a matter 

 of ordinary business prudence and a condition essen- 

 tial to best results, every dairyman should study the 

 individuality of his cows, keep a sufficient record of 

 quantity and quality of milk produced, know approxi- 



