68 DIFFERENTIATION [ch. viii 



family, there lay so much evidence that species, genera, tribes, 

 sub-families and families were so continually separated by such 

 well-marked divergent characters as leaves opposite or alternate, 

 anthers opening by slits or by pores, ovules l-2-oo in each 

 loculus, raphe dorsal or ventral, and many more such differences, 

 which allowed of no intermediate or transition forms upon 

 which natural selection might operate, which were such that one 

 could not conceive of natural selection choosing between them, 

 and which were so constant in their inorphological character — a 

 feature that one could not expect natural selection to bring forth. 

 They could only, it would appear, be the result of definite single 

 mutations, and therefore mutations must at times be large. And 

 if large in regard to these characters, which are very often of 

 "family" rank, why not in all cases? 



In May 1907, without having seen Dr Guppy's book, the 

 author published what was essentially the same theory (70), 

 largely based upon the study of the Podostemaceae, and upon 

 ten years' experience of tropical vegetation. Both authors were 

 convinced that the great importance at that time attributed to 

 adaptation was exaggerated. Natural selection was trying to 

 construct a tree from the twigs downwards. But though a tree 

 grows from the ground upwards, it always has young twigs and 

 leaves (which may be looked upon as representing genera and 

 species), though each one, when the tree is small, has a much 

 greater value in proportion to the whole organism than when the 

 tree is large. It seemed to us clear that in trying to show that 

 evolution proceeded in the order 



Small variety — Large — Species — Genus — etc. , 



people were trying to make it work backwards, and that the 

 proper order was 



Family — Tribe — Genus — Species — Variety. 



The relative rank of these groups varied as time went on. When 

 very young, the family, the genus, and the species were the same, 

 but as the family grew in size (just as with the tree mentioned 

 above) the species became of less and less relative rank when 

 compared to it. 



To turn to geographical distribution; upon the theory of 

 natural selection, the large and widely distributed genera are the 

 successes, the small and local the failures or relics. The success 

 was always put down to better adaptation to conditions, though 

 no one tried to explain how a species that derived its adaptation. 



