CH. XIV] GENERAL DISCUSSION 185 



selection is quite helpless to explain it. Good evidence is thus 

 given for differentiation. In case xxi (p. 136) the three largest 

 families are shown to occur one in each of the three great divi- 

 sions of the flowering plants ; this seems to indicate the proba- 

 bility of very large mutations in very early divergences. In 

 case XXII (p. 137) the mere fact that one can usually construct 

 dichotomous keys goes to prove differentiation. In case xxiii 

 the fact that divergence from the usual family characters is more 

 pronounced the larger the family, goes the same way. In case xxiv 

 (p. 138) the puzzling but frequent case of parallel variation in 

 one, or in two or three related, families, very difficult to explain 

 by selection, is simple to differentiation, whilst in case xxv 

 (p. 140) widespread organisms are shown to be the simpler, 

 though it does not say much for the advance in organisation 

 supposed to be the result of selection. Darwin himself puts it 

 down to their greater age, as does the writer. 



In chap. XIII a few tests based on Geographical distribution 

 are given, but the full development of this attack upon the 

 current theory of evolution must be left for the publication of a 

 book which the writer has in preparation. In case xxvi (p. 146) 

 the difficulties brought up by age and area are considered, 

 especially the fact that on the average the distribution within a 

 country goes with the distribution outside. As the conditions 

 must vary, this goes to show that gradual adaptation other than 

 physiological can have had little or nothing to do with the distri- 

 bution. Natural selection has had to call in two supplementary 

 hypotheses to explain the facts brought up about endemics and 

 their distribution in Ceylon, and these hypotheses are mutually 

 contradictory. The fact that the distribution of family surnames 

 in Canton Vaud (p. 149) also matches that of plants, including 

 endemics, goes to show that natural selection had very little to 

 do with the latter other than purely locally. In case xxvii 

 (p. 149) it is shown how contour maps may be constructed for 

 most genera, especially when they are small, and have in the vast 

 majority of cases only one centre. As no one genus takes any 

 notice of the contours of any other (p. 154), the contours can 

 hardly be determined by any local conditions. Great Britain, 

 with its great variety of conditions, has nothing but margins of 

 contours. In case xxviii (p. 154), already published, it is shown 

 how the relationships of the smaller genera and of the species in 

 a genus, in any given family, often show such great geographical 

 divergence, with its near relatives separated by distances which 



