114 TEST CASES [ch. xi 



the sharpness of definition in a small family is due to the fact 

 that the family is small, with few genera. But this does not 

 explain the fact that those genera have ahiiost without exception 

 the rank of sub-families in a large family. 



The result of this test case is thus very strongly indeed in favour 

 of the theory of differentiation as against that of natural selection 

 with gradual adaptation. 



TEST CASE X. THE PERFECTION 

 OF CHARACTERS 



The fact, which seems to have been completely ignored, that 

 structural characters are practically alwaj's shown both by 

 animals and by plants in their perfect condition, is one which is 

 simply incapable of explanation upon the ground of gradual 

 acquirement, but simple if it be the result of a sudden mutation. 

 The astonishing thing in the latter case would be to see an im- 

 perfect acquisition. The perfect condition is best shown by the 

 very widely divergent characters, like opposite or alternate leaves 

 and many others that have no intermediates, in fact most of the 

 characters shown in Appendix I. How can the divergence, under 

 natural selection, have become not only larger but more perfectly 

 marked? Supposing for the moment that an intermediate were 

 possible between alternate and opposite leaves, and that there 

 was such an adaptational urge that a plant began to progress in 

 the direction of the latter. It is clear that once the leaves began 

 to be nearly opposite, the urge would rapidly fall off, till at say 

 95 per cent of perfection it would be quite small, and almost 

 infinitesimal at 99 per cent. How comes it then that opposite 

 leaves are exactly opposite? How comes it that a drupe or a berry, 

 a capsule or a schizocarp, is always the same in structure (inci- 

 dentally, why has evolution made no apparent attempt at im- 

 proving them?), and always complete? In the same way, a 

 disadvantageous character would be unlikely to be completely 

 ■got rid of. 



It is, I think, safe to say that natural selection could not dis- 

 tinguish between 96 and 100 per cent of perfection, and that 

 there must be some other principle that is responsible for the 

 perfection that is always shown. By far the simplest explanation, 

 and the only satisfying one at present, is that the perfection is 

 due to a direct mutation. One can multiply examples to an 

 almost unlimited extent. 



