130 



HABIT AND INTELLIGENCE. 



[chap. 



through 

 descent 

 with modi 

 fication ? 



produced by slow and gradual development from perfectly- 

 simple germs ? or is the presumption in favour of the old 

 beUef, that every species has been separately created, and 

 created as we find it ? According to the " theory of develop- 

 ment," as it is usually called, all the organic species, vege- 

 table and animal, which are living or ever have lived, are 

 descended from one or a few ancestors, which had life, but 

 not organization ; and all the wondrous organization and 

 other vital properties which the various species of organisms 

 possess, over and above those powers of transforming matter 

 and energy which, as we have seen, constitute the dif- 

 ferentia of life, have been acquired by gradual modification 

 through descent for countless generations. I have pur- 

 posely stated the development theory in its most extreme 

 form. Various intermediate theories — compromises as 

 they may be called — are no doubt possible between the 

 development theory and the opposite theory of separate 

 creations. We may suppose separate ancestors, for in- 

 stance, for the animal and vegetable kingdoms, or separate 

 ancestors for each of the great primary divisions of the two 

 kingdoms, or for groups of any less magnitude. But these 

 compromises are seldom made, and are scarcely worth any 

 attention. It appears to be generally felt that the same 

 arguments which are relied on to show the strong pro- 

 bability of the common origin of chstinct though nearly 

 allied species — as, for instance, the horse and the ass — are 

 equally valid for showing the probability of a common 

 origin for all organic species whatever. 



I am a believer in the development theory to its fullest 

 extent ; and I intend in the succeeding chapters to state 

 my reasons for thinking that there is an accumulation of 

 probabilities in its favour almost amounting to proof. I 

 believe that the arguments in its favour will appear stronger 

 the more the subject is understood ; and that the objections 

 to it, on the contrary, are more apparent than real. 

 Deviations I must apologize beforehand for the deviations from 

 f °^af ^^°* strict logical method which the reader may expect. In 

 writing on any subject to which demonstration is appli- 

 cable, nothing ought to be taken as proved until it is 



I believe 

 so. 



method. 



