SINGLE CENTRES OF CREATION. 357 



with modification. A volcanic island, for instance, upheaved 

 and formed at the distance of a few hundreds of miles from 

 a continent, would probably receive from it in the course of 

 time a few colonists, and their descendants, though modi- 

 fied, would still be related by inheritance to the inhabitants 

 of that continent. Cases of this nature are common, and 

 are, as we shall hereafter see, inexplicable on the theory of 

 independent creation. This view of the relation of the 

 species of one region to those of another, does not differ 

 much from that advanced by Mr. Wallace, w r ho concludes 

 that "every species has come into existence coincident both 

 in space and time with a pre-existing closely allied species.'' 

 And it is now well known that he attributes this coincidence 

 to descent with modification. 



The question of single or multiple centres of creation 

 differs from another though allied question ; namely, 

 whether all individuals of the same species are descended 

 from a single pair, or single hermaphrodite, or whether, as 

 some authors suppose, from many individuals simultane- 

 ously created. With organic beings which never intercross, 

 if such exist, each species must be descended from a succes- 

 sion of modified varieties, that have supplanted each other, 

 but have never blended with other individuals or varieties 

 of the same species; so that, at each successive stage of 

 modification, all the individuals of the same form will be 

 descended from a single parent. But in the great majority 

 of case^, namely, with all organisms which habitually unite 

 for each birth, or which occasionally intercross, the individ- 

 uals of the same species inhabiting the same area will be 

 kept nearly uniform by intercrossing ; so. that many individ- 

 uals will go on simultaneously changing, and the whole 

 amount of modification at each stage will not be due to 

 descent from a single parent. To illustrate what I mean : 

 our English race-horses differ from the horses of every other 

 breed ; but they do not owe their difference and superiority 

 to descent from any single pair, but to continued care in 

 the selecting and training of many individuals during each 

 generation. 



Before discussing the three classes of facts, which I have 

 selected as presenting the greatest amount of difficulty on 

 the theory of " single centres of creation," I must say a few 

 words on the means of dispersal 



