PARENT AND OFFSPRING 393 



It is likely that if aU these samples of ears of corn had 

 been left to grow side by side, no such differentiation of the 

 two races would have developed. They have been separated 

 from one another only by selection and perpetuation of the 

 desired types and by elimination of the others. 



403. Artificially selected types not easily maintained. The 

 plants and animals developed artificially by man could not 

 persist long in their present form if they were removed 

 from his care. A corn field, if left from year to year, would 

 probably, even in its second year, be more conspicuous for 

 its weeds than for its corn. Farm animals, if left to shift 

 for themselves, would doubtless, in most cases, soon cease to 

 exist or would rapidly change their habits and appearance. 

 A poultry yard, if deserted by man, would soon be cleared of 

 chickens by marauding animals, by disease, or by starvation. 

 A rose garden requires constant care to prevent its losing 

 the high type of flower production desired by man. An 

 apple orchard under relaxation of care very soon becomes 

 infested by disease and reverts to relative nonproductivity. 

 Man's artificially selected types are in a condition of high 

 tension, which is soon relaxed, partly or wholly, when he 

 ceases to select and to care for them. These conditions are 

 well shown in neglected orchards and on abandoned farms, 

 where cultivated plants are gradually giving way to native 

 wild plants. 



404. Inheritance. Much that has been said bears more or 

 less directly upon the topic of inheritance. ''Heredity is 

 the rule of persistence among organisms." It is an old say- 

 ing that " like begets like," and while we know that organisms 

 vary from one generation to another, we also know that they 

 resemble one another with varying degrees of resemblance. 

 We expect individual characteristics of parents to be more or 

 less represented in the individual characteristics of offsprings. 

 Francis Galton studied in a large number of families the 

 relations between the average height of the parents and 



