98 TEST CASES [ch. x 



If we test these suppositions upon the facts, we soon find that 

 the large and "successful" families have many more "relics" in 

 them than have the small and "unsuccessful". In the Compo- 

 sitae, the largest of all, the monotypic or one-specied genera form 

 37-8 per cent of the total, while in the 151 small families containing 

 not more than ten genera each they are only 29 per cent (figures 

 twenty years old). The families with eleven to fifty genera have 

 33 per cent of monotypes, those with fifty-one to one hundred 

 have 36 per cent and those above have 39 per cent, a result which 

 agrees well with the theory of differentiation, but not with that 

 of natural selection. Even with the ditypic genera, their per- 

 centage in families up to 200 is 12-25, and 12-75 above. 



If the small genera of one or two species are to be looked upon 

 as relics of former floras, why are they so numerous? About 

 38 per cent of all genera are monotypic, and over 12 per cent 

 ditypic, so that these groups alone make up half the total number. 

 Over 80 per cent of all genera have ten or fewer species. The hollow 

 curve, as we have seen, goes so smoothly and uniformly that 

 there is no possibility of drawing a line between successes and 

 failures. The only explanation of these curves upon the theory of 

 natural selection would seem to be that selection, as indeed one 

 might expect from its name, is continually picking out fewer and 

 fewer, so that its effect will be ultimately shown (when the relics 

 have died completely out) in a vast di7ninutio7i of the numbers of 

 species and genera. In other words, it is on its way to pick out a 

 few "super-plants" from among a mass of inferiors. But if so, 

 why did nature begin with so many? Their evolution cannot be 

 explained by natural selection. The whole attempt to explain 

 things upon this theory leads to so many absurdities that it 

 becomes untenable. The simplest explanation is evidently that 

 by using the theory of gradual adaptation in structural characters 

 one is trying to work backwards. 



Every formation of a genus of two species (perhaps one may 

 be enough) increases the number of genera that may be looked 

 upon as capable of giving new genera of one, and as the larger 

 genera also may be looked upon as similarly capable, the rate of 

 production of monospecific genera will increase with the 

 size of the family. As already explained, the ones, as newcomers, 

 will be particularly slow at first in establishing themselves, so 

 that there will always be a time lag between them and the twos. 



This test also fully favours the theory of differentiation. 



