LINNEAN SOCIETY OF LONDON. 21 



fitly adapted to their environment, the problems of relationship, 

 of descent and, in short, of the origin of species become part of 

 that great study of adaptation which is the proper occupation of 

 the physiologist. These problems are bound up, not with the 

 outward seeming of an organ or organs, but with their %ise to the 

 animal in the struggle for existence, and are therefore in the first 

 place problems of function. 



In a search for the ancestry of Man and of Vertebrates generally 

 we must therefore remember that we are dealing, not with museum 

 specimens, but with living organisms, and must endeavour to learn 

 what are the essential factors in the life of the animal that give 

 it an advantage over its fellows and tend to the perpetuation of its 

 stock. 



We have really two questions to deal with, namely : — 



(1) What determines survival of type ? and, 



(2) What determines dominance of type ? 



Sui'vival is merely a question of perfection of adaptation and 

 does not necessarily imply that the type which survives becomes 

 dominant. There are many holes and corners on the surface of 

 the globe where the environment is of a very special character, and 

 in each of these we shall find some group of organisms adapted 

 for this environment and for none other. In many cases such an 

 environment is furnished by the svirface or interior of some other 

 type leading a more active existence. It is in this parasitic con- 

 dition that we get the most extreme degree of specialized adapta- 

 tion associated with degeneration of all parts rendered unnecessary 

 by the restricted range of environmental events to which the 

 organism is liable. 



Dominance of a type, on the other hand, involves wide distri- 

 bution and, in most cases, the existence of numerous species of 

 the same general characteristics under widely different conditions 

 of environment. To such a dominant type belongs the Vertebrate 

 with its highest representative, Man. There can be no doubt 

 that the evolution of such a type must have been continuous and 

 progressive. It has often been imagined that the evolution of the 

 dominant forms of life was simultaneous and not successive, and 

 was to be compared rather to the spokes of a fan than to a tree 

 with its branches diverging from a common stem. Such a fan- 

 like evolution could only occur with a complete separation of 

 environments. It is as difficult to conceive that the Vertebrate 

 was evolved from a primitive worm-like organism which shot up 

 past the more highly developed Arthropoda, as it is to believe that 

 mankind is destined to be replaced by some beast that is now 

 being evolved from lower groups in the depths of the sea. But 

 what do we mean by speaking of lower and higher groups ? The 

 idea involved in this antithesis is the same as that included in the 

 term " dominance." The positioo of any type in the animal scale, 

 the question whether it is to win in life's struggle, is determined 



