172 GENERAL DISCUSSION [ch. xiv 



gent mutation), that families, genera, and species may any of 

 them be the result of a single 7nutation, more divergent in genera 

 than in species, in families than in genera. These ideas receive 

 great confirmation in the actual structural differences that 

 separate plants. As one goes up the scale from species to family, 

 the divergence of the characters of separation increases upon the 

 whole, as is at once shown by any good dichotomous key. A 

 feature of special interest is that the divergences become more 

 and more such as allow of no intermediates or transitions at all, 

 as for example, a berry and a drupe, an achene and a follicle, an 

 anther with slits and one with pores. But if this be the case, the 

 character, one or the other of a divergent pair, must have 

 appeared at one step, so that, so far as one can see, natural 

 selection can have had no hand in its appearance. The higher 

 that one goes in the direction of the family, the less adaptational 

 value can one find in the characters, so that the less is the handle 

 that is offered to natural selection. Competition is greatest 

 among individuals, less among species, still less among genera, 

 and so on upwards. Yet the distinctions become greater along the 

 same route, and the puzzling question is put as to how the 

 diminished competition can bring about the larger and more 

 permanent distinctions. Why also are these characters of so 

 slight (if any) functional use? If natural selection be the active 

 agent in evolution, it must have been working at its highest 

 pressure among the highest groups to separate them as they are 

 separated, and also must have been working all the time to pick 

 out characters with greater adaptational value; whereas in fact 

 one finds the characters to be of less and less value as one goes 

 upwards in the supposed track of natural selection. In seventy- 

 five years no one has been able to prove any functional value for 

 them. The uniformity of the statistics of the various continents 

 and other large areas (66, p. 180) in the proportions of genera 

 of various sizes, in their distribution, in the relative sizes of 

 families and genera, etc., shows that one area is just like another, 

 and that evolution must be going on in the same orderly way 

 in all. 



Though going to Ceylon an enthusiastic supporter of natural 

 selection, the author found it needful to change his views after 

 some years of tropical experience, both in the forest, and as the 

 result of a minute study of the Podostemaceae (p. 18). Though at 

 first glance looking as if they showed great adaptational dif- 

 ferences, these plants all live under the most amazingly uniform 



