472 THEORY OF PROGRESSION. chap. xxiv. 



botanists, as before explained; that whatever may be the 

 nature of the species-making power or law, its effects are of 

 such a character as to imitate the results which variation, 

 guided by natural selection, would produce, if only wc could 

 assume with certainty that there are no limits to the varia- 

 bility of species. But as the anti-transmutationists are per- 

 suaded that such limits do exist, they regard the hj-pothesis 

 as simply a provisional one, and expect that it will one day 

 be superseded by another cognate theory, which will not 

 require us to assume the former continuousness of the 

 links which have connected the past and present states 

 of the organic world, or the outgoing with the incoming 

 species. 



In like manner, many of those who hesitate to give in 

 their full adhesion to the doctrine of progression, the other 

 twin branch of the development theory, and who even object 

 to it, as frequently tending to retard the reception of new 

 facts supj)Osed to militate against opinions solel}^ founded on 

 negative evidence, ai'e, nevertheless, agreed that on the whole 

 it is of great service in guiding our sjieculations. Indeed, it 

 cannot be denied that a theory which establishes a con- 

 nection between the absence of all relies of vertebrata in the 

 oldest fossiliferous rocks, and the presence of man's remains in 

 the newest, which affords a more than plausible explanation of 

 the successive appearance in strata of intermediate age of the 

 fish, reptile, bird, and mammifer, has no ordinary claims to 

 our favor as comprehending the largest number of positive 

 and negative facts gathered from all parts of the globe, and 

 extending over countless ages, that science has perhaps ever 

 attempted to embrace in one grand generalization. 



But will not transmutation, if adopted, require us to 

 include the human race in the same continuous series of 

 developments, so that we must hold that man himself has 

 been derived by an unbi'oken line of descent from some one 



