C. — GEOLOGY. 



75 



tinuously moved by a certain principle inherent in themselves, arrive 

 at a certain end.' In other words, a race once started on a certain 

 course, will persist in that course; no matter how conditions may 

 change, no matter how hurtful to the individual its o\yn changes 

 may be, progressive or retrogressive, up hill and down hill, straight 

 as a Eoman road, it will go on to that appointed end. Nor is 

 it only palaeontologists who think thus. Professor Duerden has 

 recently written, ' The Nagelian idea that evolutionary changes have 

 taken place as a result of some internal vitalistic force, acting altogether 

 independently of external influences, and proceeding along definite Hnes, 

 irrespective of adaptive considerations, seems to be gaining ground at 

 the present time among biologists ' (1919, Jonrn. Genetics, viii. p. 193). 

 The idea is a taking one, but is it really warranted by the facts at our 

 disposal? We have seen, I repeat, that succession does not imply 

 evolution, and (gi'anting evolution) I have claimed that seriation can 

 occur without determinate variation and without predetermination. It 

 is easy to see this in the case of inanimate objects subjected to a con- 

 trolling force. The fossil-collector who passes his material through a 

 series of sieves, picking out first the larger shells, then the smaller, 

 and finally the microscopic loraminifera, induces a seriation in size by 

 an action which may be compared to the selective action of successive 

 environments. There is, in this case, predetermination imposed by an 

 external mind; but there is no determinate variation. You may see in 

 the museum at Leicester a series beginning with the via strata of the 

 Roman occupants of Britain, and passing through all stages of the 

 tramway up to the engineered modern railroad. The unity and 

 apparent inevitability of the series conjures up the vision of a world- 

 mind consciously working to a foreseen end. An occasional experiment 

 along some other line has not been enough to obscure the general trend ; 

 indeed, the speedy scrapping of such failures only emphasises the idea 

 of a determined plan. But closer consideration shows that the course 

 of the development was guided simply by the laws of mechanics and 

 economics, and by the history of discovery in other branches of science. 

 That alone was the nature of the determination; and predetermination, 

 there was none. From these instances we see that selection can, indeed 

 must, produce just that evolution along definite lines which is the 

 supposed feature of orthogenesis. 



The arguments for orthogenesis are reduced to two : first, the diffi- 

 culty of accounting for the incipient stages of new structures before 

 they achieve selective value ; second, the supposed cases of non-adaptive 

 or even — as one may term it — counter-adaptive growth. 



The earliest discernible stage of an entirely new character in an 

 adaptive direction is called by H. F. Osborn a ' rectigradation ' (1907), 

 and the term implies that the character will proceed to develop in a 

 definite direction. As compared with changes of proportion in exist- 

 ing characters (' allometron,' Osborn), rectigradations are rare. Osborn 

 applies the term to the first signs of folding of the enamel in the teeth 

 of the horse. Another of his favourite instances is the genesis of horns 

 in the Titanotheres, which he has summarised as follows : ' (a) from 

 excessively rudimentary beginnings, i.e. rectigradations, which can 



