THE THEORY OF DESCENT 251 



we know nothing of an evolutionary character in the 

 problematic pedigree of the organisms, as we shall see more 

 fully hereafter. The term " theory of descent ' is there- 

 fore less open to objection than is the usual English term. 

 The word transformism, as used by the French, would also 

 be a very good title. 



The theory of descent is the hypothetic statement that 

 the organisms are really allied by blood among each other, 

 in spite of their diversities. 1 The question about their 

 so-called monophyletic or polyphyletic origin is of secondary 

 importance compared with the statement of relationship in 

 general. 



There are two different groups of facts which have 

 suggested the idea of transformism : none of these facts can 

 be said to be conclusive, but there certainly is a great 

 amount of probability in the whole if taken together. 



The first group of evidences which lead to the hypothesis 

 of the real relationship of organisms consists of facts relat- 

 ing to the geographical distribution of animals and plants and 

 to palaeontology. As to geography, it seems to me that the 

 results of the floral and faunal study of groups of islands 



1 We prefer this unpretending definition of the theory of descent to every 

 other. As soon as one introduces into the definition the concept of the 

 " transmutability of species," the term "species" would require a special 

 definition, and that would lead to difficulties which it is unnecessary 

 to deal with for our main purposes. It has been remarked by Krasan, 

 (Aiisickten und Gesprache iiber die indimduelle und specifische Gestaltung 

 in der Natur] and by several other writers, that the problem of 

 mutability or immutability of course relates to the individuals in the first 

 place. I should like to add to this remark that the possibility must be 

 admitted of the individuals being transmutable, whilst the " species " 

 are not transmutable at the same time, the line of the " species " being a fixed 

 order, through which the "individuals" have to pass in the course of their 

 generations. What is meant here will become clearer, when we study the 

 different possible aspects of "phylogeny." 



