CH. XI] B. MORPHOLOGICAL 113 



ancestry. It would also seem as if there were a tendency in each 

 family for mutation to become less pronounced as time goes on, 

 so that the appearance of what we usually call family characters 

 (list in Appendix I) becomes less frequent in proportion to the 

 total of characters that appear. On the whole, there is more room 

 for wider divergences the nearer one is to the starting-point of 

 the family, i.e. to the original genus which gave rise to it, upon 

 the theory of differentiation. Upon that of natural selection, it 

 has always been a great difficulty to explain why the divergences 

 became greater the higher one went in the key from species up- 

 wards. Why should natural selection cause the disappearance of 

 just those forms necessary to make the divergence increase? This 

 is inexplicable by natural selection, working upwards from small 

 differences, but simple to differentiation, working the other way. 



This being the expectation, we have only to look at Appen- 

 dix III which gives the distinguishing characters of the two genera 

 in those families that contain two only, to see that the facts 

 agree with what was expected. The divergences are obviously of 

 the same rank as those given in Appendix I as being "family" 

 characters. If, on the other hand, one compare the generic 

 characters in larger and larger families, one finds that as one goes 

 up the scale, the genera, as one will expect under the theory of 

 divergent mutation, get closer and closer together as new ones are 

 "squeezed in" among the old. In a really big family, like the 

 Umbelliferae, Compositae, or Gramineae, it is a familiar ex- 

 perience that it is as difficult to make out the genus, as in a small 

 family to make out the species. 



It is clear that we have not properly taken into consideration 

 the relative rank of genera and other groups. In a very large 

 family, where the genera have become closer and closer together 

 by the continual appearance of new ones, the generic rank is 

 evidently lower than it is in a normal small family. The ranks of 

 all divisions in the classification, whether tribes, families, or 

 genera, depend to a very great extent upon their relative sizes in 

 their circles of relationship. This conception of relative rank has 

 gone neglected during the reign of natural selection, to which a 

 genus is simply a generic stage upon the upward road. 



If, on the other hand, the small family is to be regarded as a 

 relic, as is done by the supporters of selection, it becomes neces- 

 sary for them to explain why the divergences of the two or three 

 genera that are left is so great, and equal to the divergence of the 

 sub-families in a large family. Often one hears people say that 



WED 8 



