484 POPULAR SCIENCE MONTHLY 



once that adaptive characters are older than the non-adaptive char- 

 acters. This is true, even though the adaptive character itself be a 

 relatively recent one. The flying-fishes flew before the group was 

 split up into thirty species. Yet the enlargement of the fins of these 

 fishes is one of the latest products in fish evolution. 



The species of Hawaiian birds of the family of Drepanidse are 

 among the latest results of bird development. Yet these birds were 

 divided into genera characterized by the form of the bill, each type of 

 bill being adapted to a special purpose long before the present actual 

 species were themselves differentiated. 



All the orioles build hanging nests, and all are adapted alike in 

 structure and instinct to their mode of life. All the sparrows and 

 finches have bills fitted for cracking seeds. And these features of 

 adaptation preceded the subdivision of orioles or sparrows into their 

 present genera and species. In general, the traits by which we dis- 

 tinguish species are non-adaptive characters, while the features of 

 adaptation are most distinctly traceable in structures common to many 

 species, the characters of genera or of families in zoology. 



But in this we find certain paradoxes. In studying the characters 

 of members of a zoological family, we find that the most distinctly 

 adaptive characters are relatively recent. It is a truism that physi- 

 ological characters have a lower systematic value than characters not 

 related to the character of life processes. The traits that fit ani- 

 mals for a special kind of food or for a special kind of topography are 

 recognized as of low value in taxonomy. In other words, special 

 adaptations are of relatively recent origin. General adaptations are 

 older than special adaptations. Hence they have a higher value in 

 classification. A flying-fish is fitted to swim in the water before it is 

 adapted to leap in the air. But all general adaptations began some 

 time as special ones. General adaptations have become so ingrained in 

 the life of animals that they are, in a sense, invisible to the systematist. 

 He passes them by as matters of course, directing his attention to 

 special adaptations or to special peculiarities which seem to be devoid 

 of utility. The ancient adaptations are not even considered as adapta- 

 tions at all, when we say that adaptive or physiological characters 

 have a low value in classification. And it is from this fact that the 

 seeming paradox arises. 



Again the adaptive character in the race or species may appear to 

 be of very recent origin. The Southdown sheep of England had 

 tawny faces before they acquired their present traits of wool or mutton. 

 The explanation of such cases is this : an adaptation is never finished, 

 a more rigid selection may at any time enforce a more rigid adapta- 

 tion. Natural selection acts as a constant influence. It may be 

 varied or intensified under new circumstances, as when it is directed by 

 the will of man, when it becomes artificial selection. And under the 



