CH. XIV] GENERAL DISCUSSION 179 



whilst at the same time no transitions are possible, a fact which 

 would indicate that all the characters were due to direct muta- 

 tion. How, then, was the family Rubiaceae, whose actual general 

 characters are those shown in the brackets, evolved by aid of 

 natural selection? If all these vagaries are to be explained on the 

 supposition that morphological necessities override selection, 

 there is nothing at all of structural nature left for selection to act 

 upon. The selectionist is content, and seems to think that his 

 case, that evolution is due to natural selection, is proved, if he 

 can explain a single, and probably very minor character, upon 

 that supposition. He forgets that it also has to explain the corre- 

 lated characters of a whole family or other systematic group, to 

 say nothing of the great differences that characterise the great 

 divisions of the vegetable kingdom like ferns, mosses, and liver- 

 worts, as well as the flowering plants. One cannot employ one 

 machinery to explain one feature or one portion of the vegetable 

 kingdom, another for another. 



There is no evidence to show that natural selection is collective 

 in its action rather than individual. It is obviously the latter in 

 daily life, and the work quoted on p. 166 shows that it is probably 

 the same among plants. It seems, therefore, that once the idea 

 that adaptation — ultimately reducible to the chance appearance 

 of favourable variations — is mainly responsible for the distribu- 

 tion of plants and animals has given way to a more scientific 

 conception, the study of plant distribution and of its dynamics 

 will become associated to that of human populations, each giving 

 valuable aid and assistance to the other. 



Plants seem to behave like a mixed and more or less casual 

 population expanding in a country where there are barriers of 

 many kinds to interfere with the regularity, and where the dis- 

 tribution is determined in detail by natural selection, working 

 upon the individuals. The same kind of thing has marked the 

 distribution of races in Europe, etc. We have seen that it seems 

 to pick out a mixture, not a type, and we may add to this the 

 curious fact that has lately been exciting some interest, that one 

 kind of cotton may do best when mixed with another (79). 

 This fact may have important bearings upon racial intermingling. 

 One thing at least seems fairly certain, that a whole group A will 

 not conquer and destroy a whole group B, but that the result 

 will be an intermingling of the individuals of both that are best 

 suited to the conditions at the time and place. 



Nothing but sudden mutation, usually large, will explain why 



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