NATURE 



[May 6, 1880 



that \\hich they worshipped. It is only in this way that we 

 shall acquire the means of judging whether the movement 

 we have witnessed is a mere eddy of fashion, or truly one 

 with the irreversible current of intellectual progress, and, 

 like it, safe from retrogressive reaction. 



Every belief is the product of two factors : the first is 

 the state of the mind to which the evidence in favour of 

 that belief is presented ; and the second is the logical 

 cogency of the evidence itself. In both these respects 

 the history of biological science during the last twenty 

 years appears to me to afford an ample explanation of the 

 change which has taken place ; and a brief consideration 

 of the salient events of that history will enable us to 

 understand why, if the "Origin of Species" appeared now, 

 it would meet with a very different reception from that 

 which greeted it in 1S59. 



One-and-twenty years ago, in spite of the work com- 

 menced by Hutton and continued with rare skill and 

 jjatience by Lyell, the dominant view of the past history 

 of the earth was catastrophic. Great and sudden physical 

 revolutions, wholesale creations and extinctions of living 

 beings, were the ordinary machinery of the geological epic 

 brought into fashion by the misapplied genius of Cuvier. 

 It was gravely maintained and taught that the end of 

 every geological epoch was signalised by a cataclysm, by 

 which every living being on the globe was swept away, to 

 be replaced by a brand-new creation when the world re- 

 turned to quiescence. A scheme of nature which appeared 

 to be modelled on the likeness of a succession of rubbers of 

 whist, at the end of each of which the players upset the table 

 and called for a new pack, did not seem to shock anybody. 

 I may be wrong, but I doubt if at the present time there 

 is a single responsible representative of these opinions left. 

 The progress of scientific geology has elevated the funda- 

 mental principle of uniformitarianism, that the explanation 

 of the past is to be. sought in the study of the present, into 

 the position of an axiom ; and the wild speculations of 

 the catastrophists, to which we all listened with respect a 

 quarter of a century ago, would hardly find a single 

 patient hearer at the present day. No physical geologist 

 now dreams of seeking outside the ranges of known natural 

 causes for the explanation of anything that happened 

 millions of years ago, any more than he wojld be guilty 

 of the like absurdity in regard to current events. 



The efiect of this change of opinion upon biological 

 speculation is obvious. For, if there have been no 

 periodical general physical catastrophes, what brought 

 about the assumed general extinctions and re-creations of 

 life which are the corresponding biological catastrophes .' 

 And if no such interruptions of the ordinary course of 

 nature have taken place in the organic, any more than in 

 the inorganic, world, what alternative is there to the 

 admission of Evolution ? 



The doctrine of Evolution in Biology is the necessary 

 result of the logical application of the principles of uniformi- 

 tarianism to the phenomena of life. Darwin is the natural 

 successor of Hutton and LycU, and the " Origin of Species" 

 the natural sequence of the " Principles of Geology." 



The fundamental doctrine of the " Origin of Species," 

 as of all forms of the theory of Evolution applied to 

 biology, is "that the innumerable species, genera, and 

 families of organic beings with which the world is 

 peopled have all descended, each within its own class or 



group, from common parents, and have all been modified 

 in the course of descent." ' 



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

 living animals 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 Modification, as]it is sometimes called, that all plants 

 and animals, however different they may now be, must, 

 at one time or other, have been connected 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. Darvvin's work ran more directly 

 counterto theprepossessionsof naturalists twentyyears ago 

 than this. And such prepossessions were very excusable, 

 for there was undoubtedly a great deal to be said, at 

 that time, in favour 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 con- 

 troversies, but I must state the simple fact that the dis- 

 tinctions in cerebral and other characters, which were 

 so hotly affirmed to separate man from all other animals 

 in 1S60, 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 struc- 

 tural gaps asserted to exist between one group of animals 

 and another were by no means fictitious ; and, when such 

 structural breaks were real, Mr. Darwin could account 

 for them only by supposing that the intermediate forms 

 which once existed had become extinct. In a remarkable 

 passage he says : — 



" We may thus account even for the distinctness of 

 whole classes from each other — for instance of birds from 

 all other vertebrate animals — by the belief that many 

 animal forms of life have been utterly lost, through which 

 the early progenitors of birds were formerly connected 

 with the early progenitors of the other vertebrate 

 classes."' 



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 for- 

 saking of the paths of " Baconian induction." 



But the progress of knowledge has justified Mr. Darwin 

 to an extent which could hardly have been anticipated. 

 In 1862, the specimen of Afv/iaopUr}'x, which until the 

 last two or three years has remained unique, was dis- 

 covered ; and it is an animal which, in its feathers and 

 the greater part of its organisation, is a veritable bird, 

 while, in other parts, it is as distinctly reptilian. 



In 186S, I had the honour of bringing under your notice, 

 in this theatre, the results of investigations made, up to 

 that time, into the anatomical characters of certain ancient 



^ " Origin of Species," ed. i, p. 457. 

 = "Origin of Species," ed, i, p. 458. 

 3 " Origin of Species," ed. i, p. 431. 



