584 BIOLOGY AND HUMAN LIFE 



kind of food or another, sharpness of senses (beyond a certain 

 point), muscular ability, swiftness in running. Still other dif- 

 ferences are of great importance to the race or to civilized 

 society— more or less intelligence (especially below certain 

 limits), ability to learn how to cooperate with the rest of the 

 community, abihty to do productive work, ability to become an 

 honest citizen, and others. How do these differences show them- 

 selves practically? Hundreds of thousands of people are so 

 feeble-minded or so unsteady that they cannot be relied upon 

 to earn their living or to be at large. Some people are so incom- 

 petent and so unreliable that they are constantly getting into 

 trouble, or making trouble for others, through committing crime 

 or in some other way. Now it is very likely that many of those 

 who get into trouble or commit crime or are incompetent suffer 

 because they had not the right opportunities to learn better 

 control. And we have to make a distinction between qualities 

 (good or bad) that are developed through neglect or favor- 

 able environment — acquired characters— and those that appear 

 because the individual comes from a particular strain of germ— 

 inherited characters. But it is quite clear that there is a seri- 

 ous proportion of our population that is socially undesirable 

 because of inherited defects or shortcomings. 



419. Heredity in man. Heredity works the same in man as it 

 does among other mammals, or indeed among other organisms in 

 general. For a number of characters it has been possible to show 

 that Mendel's principles apply in man as well as in peas or in- 

 sects. Some of these characters are given in the table on page 585. 

 It is also true for man, as it is for other organisms, that the 

 effects of practice or disease, the effects of changes in the en- 

 vironment, of mutilations, of nutrition, and so on — acquired 

 characters in general — are not transmitted to offspring. Study- 

 ing music will not increase the amount of musical ability in the 

 next generation; musical ability "runs in families," very much 

 as does a peculiar shape of lip or hand. The family of the great 

 musician Johann Sebastian Bach had fine musicians in every 

 generation as far as the records could be obtained. So far as 



