HEREDITY 545 



most skillful methods. So far as ordinary laws of evolution go 

 there is no doubt about it, and we can with confidence assert 

 our ability to maintain a desirable type indefinitely ; but are 

 there biological considerations outside of mere variability that 

 tend to extinction ? Do species " wear out," or do they come to 

 an untimely end by accident only ? 



In the opinion of the writer we do not possess sufficient reli- 

 able data on this point to warrant confident assertion. It is 

 probably true that species have disappeared off the earth at a 

 rate not equaled by the production of new species. It is true, 

 too, that among domestic animals some of the most valuable 

 lines have disappeared in spite of the most energetic efforts to 

 preserve them. 1 In the instance given below the extinction is to 

 be definitely ascribed to barrenness, a defect perfectly well 

 known to breeders, and considered by them at the time as fortu- 

 nate, in the interest of high prices, they evidently not appreciating 

 the inevitably fatal consequences of racial barrenness. 



On the other hand, many species have persisted from remote 

 times practically unchanged in type (oaks and tulip trees), and 

 as we are fully informed as to some of the causes that resulted 

 in the extinction of favorites, like the unfortunate family of Short- 

 horns just 'mentioned, we are warranted in hoping that species 

 in general may be maintained indefinitely. 



The conclusion is forced upon us that reliable information is 

 wanting as to whether all types can be indefinitely maintained. 

 No proper attempt was made to save the Duchess family. Its 

 inherent weakness was counted its chief virtue, and there could 

 be but one conclusion. But was its fertility a waning character, 

 which no amount of selection could have strengthened ? Again 

 we say that our knowledge is insufficient for the answer. 



Summary. Heredity is not the relation between the offspring 

 and his parent simply, but the relation between him and the 

 whole back ancestry. The characters of the individual are the 

 characters of the race. Some are well developed, others are 

 undeveloped or latent, but all are there in some degree. 



1 For example, the Duke and Duchess Shorthorns, the most famous family of 

 any breed, so famous that a heifer brought $40,600 at the New York Mills sale 

 in 1873. 



