178 GENERAL DISCUSSION [ch. xiv 



selection of favourable variations, whereas the recent progress of 

 the physical sciences goes to show that in their case the whole 

 evolution is proceeding upon a well-marked "mathematical" 

 programme. The theory that is beginning to be indicated in the 

 work that has been described above, goes to show that evolution 

 also, one of the greatest recent facts of the physical universe, has 

 proceeded upon a course underlying which there is some physical 

 law, probably electrical, which also can be expressed in mathe- 

 matical terms. This has already been shown to be the case with 

 the law of age and area, which is evidently only a corollary of 

 the larger law thus indicated. 



To go on to some of the minor objections to natural selection, 

 of which there are a great number, it is impossible to explain by 

 its aid the characters that divide species, and the difficulty be- 

 comes greater and greater as we go up the scale through genus to 

 family and beyond, while at the same time the distinctions 

 become also greater and greater, and any functional value to be 

 attached to them becomes less and less, whilst possible transi- 

 tions become rarer and rarer. 



It is almost impossible to explain the perfection in which the 

 characters show themselves, a clean-cut perfection which again 

 becomes more and more marked the higher we go (p. 76). If 

 natural selection cannot perfect either of such divergent charac- 

 ters as opposite leaves and alternate (showing a definite phyllo- 

 taxy), their perfection must be due to heredity, or to direct 

 mutation, for there cannot be a gradual passage from one to the 

 other. In the latter case natural selection is excluded, while in 

 the former one has to remember that the way in which the 

 ancestor obtained the perfect character must be explained by 

 natural selection. There is the further difficulty that so often the 

 two characters occur side by side in species of the same genus. 

 As a special case we may take the family Rubiaceae (p. 118). 

 Members of the family can be found showing alternate leaves (as 

 against opposite, the "family" character), pinnate (entire), 

 intrapetiolar stipules (interpetiolar), male and female flowers (^), 

 zygomorphic flowers (regular), solitary axillary flowers (cymes 

 or heads), 8-merous flowers (5-4), convolute calyx (open), 

 descending aestivation of corolla (convolute or valvate), anthers 

 by pores (slits), ovary 10-locular (2), endosperm none (present), 

 ruminate (not), whilst the whole family shows an amazing variety 

 in the fruit. All the characters that distinguish the family are 

 found at times to be replaced by something quite different, 



