394 NATURAL SCIENCE [June 



of modifications ' being the sole quest of the Neo-Lamarckians. If 

 this is so, they are working on a part of evolution which Darwin 

 confessedly found difficult to elucidate, but which can yield 

 nothing opposed to his views. Indeed, as Mr Henslow himself has 

 insisted by means of an admirable quotation from Darwin, "... 

 Natural Selection . . . has no relation whatever to the primary 

 cause ^ of any modification of structure." It follows that there can 

 be no antagonism between two positions so distinct. In fact, the 

 Neo-Lamarckian is included in the other larger, Darwinian position. 



But the second definition involves something more than a study 

 of the primary causes of modification, since causes which bring 

 about, as well as those which originate, variations are here included. 

 In the third position Mr Henslow accepts for himself the views 

 which I formerly ascribed to him, and eliminates natural selection 

 as a species-forming, though admitting it as a possible species- 

 separating, force. Which of the three positions he would have us 

 accept, it is hard to infer, either from his reply or from his works. 



He further says : " There is no necessity for all the individuals 

 to be equally, though they be all similarly, modified. Natural 

 Selection need not enter so timidly as he imagines, but may boldly 

 kill off as many as it pleases, and thus ' become a factor of some 

 importance'; but this has nothing whatever to do with the primary 

 cause of the origination of the definite variations. These being now 

 known, it is at once seen that Natural Selection plays no part at all 

 in causing them." Mr Henslow here seems to hold that variations, 

 when occurring in any given variety, may vary in degree, but that 

 this degree will remain constant in each ; that, given a certain 

 number of variations from a certain point, each one of these will 

 continue to vary at the same rate whether other variations are 

 present or not ; and, consequently, that " Natural Selection thus 

 applied only separates varieties and makes them more distinct for 

 the benefit of the classifier," but plays no part directly or indirectly 

 in forming these divergences ; it only eliminates the unsuccessful 

 intermediate varieties when formed. 



Now the objection that I raised to this position was, that as there 

 are at least as many eminent authorities who hold opposite views 

 and are not convinced by the facts adduced in support of this con- 

 tention, it is not enough to assert that it is so ; it must further be 

 shown that where Natural Selection is not able to act, varieties have 

 diverged and adapted themselves as rapidly as similar varieties have 

 in a control experiment, in which Natural Selection has been given 

 full opportunity of acting. Again, when I questioned the validity 

 of assuming that definite variations are necessarily opposed to 

 Natural Selection, he, in reply, mentions what I already knew, that 



^ Spaced type mine. 



