252 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



are to be mentioned in the first place. If, indeed, on each 

 of the different islands, ABC and D, forming a group, 

 the species of a certain genus of animals or plants are 

 different in a certain respect, and show differences also 

 compared with the species living on the neighbouring 

 continent, of which there is geological evidence that the 

 islands once formed a part, whilst there is no change in 

 the species on the continent itself for very wide areas, then, 

 no doubt, the hypothesis that all these differing species 

 once had a common origin, the hypothesis that there is a 

 certain community among them all, will serve to elucidate 

 in some way what would seem to be very abstruse without 

 it. And the same is true of the facts of palaeontology. 

 In the geological strata, forming a continuous series, you 

 find a set of animals, always typical and specific for every 

 single stratigraphical horizon, but forming a series just as 

 do those horizons. Would not the whole aspect of these 

 facts lose very much of its peculiarity if you were to 

 introduce the hypothesis that the animals changed with 

 the strata ? The continuity of life, at least, would be 

 guaranteed by such an assumption. 



The geographical and geological evidences in favour of 

 the theory of descent are facts taken from sciences 

 which are not biology proper ; they are not facts of the 

 living but only facts about the living. That is not quite 

 without logical importance, for it shows that not biology 

 alone has led to the transformism hypothesis. Were it other- 

 wise, transformism might be said to be a mere hypothesis 

 ad hoc ; but now this proves to be not the case, though 

 we are far from pretending that transformism might be 

 regarded as resting upon a real causa vera. 



