364 Professor Huxley [April 9, 



innumerable species, genera, and families of organic beings witb 

 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." f 



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 grouj)S 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 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 

 controversies; but I must state the simple fact that the distinctions in 

 cerebral and other characters, which were so hotly affirmed to sepa- 

 rate man from all other animals in 1860, have all been demonstrated 

 to be non-existent, and that the contrary doctrine is now universally 

 accepted anil taught. 



But there were other cases in which the wide structural 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 inter- 

 mediate forms which once existed had become extinct. In a remark- 

 able 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 



* 'Origin of Species,' cd. 1, p. 457. 

 t Ibid. p. 458. 

 X Ibid. p. 431. 



