Reduced Organs 103 



in danger of being blown away by strong winds; wings are 

 therefore of disadvantage to them. We find accordingly 

 that most such insects cannot fly. Yet they are not only 

 similar to the insects of neighboring continents in their gen- 

 eral form and structure, but they all retain rudiments or 

 vestiges of wings. The loggerhead duck of South America 

 is unable to fly. Its wings are small and can only be flapped. 

 Whatever value these wings may be to their possessor, they 

 are obviously reduced wings and suggest that the ancestors 

 of this bird in some remote past had functional wings. We 

 cannot of course " prove " that the wings of the loggerhead 

 duck have been reduced in this sense. We know, however, 

 that they are reduced wings because the young of this spe- 

 cies strangely enough have fully developed wings with which 

 they can fly. Here the reduction takes place in the course 

 of each individual's lifetime, as with the tail of the individ- 

 ual human being (see Fig. 52). 



The skeleton of the horse's foot contains bones that have 

 been described as corresponding to undeveloped toes. Again, 

 as with any historical problem, we cannot " prove " that 

 the ancestor of the horse had real toes corresponding to these 

 bones (except as we infer, from the series of fossils, the past 

 history of the tribe; see page 43). Nevertheless, we do find 

 occasionally a colt that has two smaller toes behind the hoof 

 — that is, these useless bones sometimes overdevelop and re- 

 veal their nature as toes. A similar condition is sometimes 

 found in pigs and in other hoofed animals. Such outcrop - 

 pings of latent characters are quite analogous to so-called 

 " throw-backs " among domesticated animals and among 

 human beings. We recognize a trait that was present in a 

 remote ancestor of a person, but not in the immediate an- 

 cestors, and accept it as an indication of heredity or kinship 

 because we happen to know the family history. We should 

 be prepared to accept such appearances as indications of 

 kinship where the family history is not accessible to us. 



The blindness of cave animals has been long known. 

 This is so much in keeping with our common assumption of 

 fitness in the structure of living things that it has been ac- 



