340 THE POPULAR SCIENCE MONTHLY. 



And, in view of the facts of geology, it follows that all living ani- 

 mals and plants " are the lineal descendants of those which lived long 

 before the Silurian epoch."* 



It is an obvious consequence of this theory of Descent with Modi- 

 fication, as it is sometimes called, that all plants and animals, however 

 different they may now be, must, at one time or other, have been con- 

 nected by direct or indirect intermediate gradations, and that the 

 appearance of isolation presented by various groups of organic beings 

 must be unreal. 



No part of Mr. Darwin's work ran more directly counter to the 

 prepossessions of naturalists twenty years ago than this. And such 

 prepossessions were very excusable, for there was undoubtedly a great 

 deal to be said, at that time, in favor of the fixity of species and of 

 the existence of great breaks, which there was no obvious or probable 

 means of filling up, between various groups of organic beings. 



For various reasons, scientific and unscientific, much had been made 

 of the hiatus between man and the rest of the higher mammalia, and it 

 is no wonder that issue was first joined on this part of the controversy. 

 I have no wish to revive past and happily forgotten controversies, but 

 I must state the simple fact that the distinctions in cerebral and other 

 characters, which were so hotly affirmed to separate man from all other 

 animals in 1860, have all been demonstrated to be non-existent, and 

 that the contrary doctrine is now universally accepted and taught. 



But there were other cases in which the wide structural gaps as- 

 serted to exist between one group of animals and another were by no 

 means fictitious ; and, when such structural breaks were real Mr. Dar- 

 win could account for them only by supposing that the intermediate 

 forms which once existed had become extinct. In a remarkable pas- 

 sage he says : " We may thus account even for the distinctness of 

 whole classes from each other for instance, of birds from all vertebrate 

 animals by the belief that many animal forms of life have been ut- 

 terly lost, through which the early progenitors of birds were formerly 

 connected with the early progenitors of the other vertebrate classes." f 



Adverse criticism made merry over such suggestions as these. Of 

 course it was easy to get out of the difficulty by supposing extinction ; 

 .but, where was the slightest evidence that such intermediate forms 

 between birds and reptiles as the hypothesis required ever existed ? 

 And then probably followed a tirade upon this terrible forsaking of 

 the paths of " Baconian induction." 



But the progress of knowledge has justified Mr. Darwin to an ex- 

 tent which could hardly have been anticipated. In 1862 the specimen 

 of Archcwpteryx, which until the last two or three years has remained 

 unique, was discovered ; and it is an animal which, in its feathers and 

 the greater part of its organization, is a veritable bird, while, in other 

 parts, it is as distinctly reptilian. 



* " Origin of Species," first edition, p. 458. f Ibid., p. 431. 



