CH. x] A. NUMERICAL 93 



It is difficult to understand, upon the theory of natural selec- 

 tion, how the long tails of genera that contain only one or very 

 few species, and that occur in all but the very smallest families 

 (and are often indicated there), ever came to be evolved at all. 

 Natural selection looks upon them as the failures, and upon the 

 large genera with many species as the successes; the latter are 

 also widely distributed about the world in practically all cases. 

 But ivhy should a genus with many species occupy a large area? 

 There must, upon the adaptation theory, have been in it a mar- 

 vellous generic adaptation. If we take the first hundred genera in 

 my Dictionary (5th ed.) with fifty or more species, half of them 

 show a distribution right round the world, and at least half the 

 remainder cover immense areas. The smallest ranges are those of 

 Acantholimon (Eastern Mediterranean) and Agathosnia and Aloe 

 (South Africa). But, with ranges like this, these large genera 

 must be very old, to have reached so many continents before 

 communications were broken, and how did thev come to find, in 

 those early times, so great a variety of conditions as to lead to so 

 many sjDecies, at a time when conditions are usually supposed to 

 have been much more uniform than now? 



If the small genera of one or a very few species are to be looked 

 upon as relics, why are there so many of them, and wh}^ do their 

 numbers increase tow^ards the bottom? It was shown (in 66, 

 p. 185) that out of 12,571 genera of flowering plants, 4853, or 

 38-6 per cent, had only one species each, 12-9 per cent had two 

 species, and 7-4 per cent had three. The numbers diminish up- 

 wards, following the regular hollow curve, shown not only by the 

 grand total, but by each individual family down to quite small 

 ones. The larger the family, the more accurately does it show the 

 hollow curve, a fact which does not favour the view that the tail 

 of small genera is composed of relics. Why should a "successful" 

 family have so many? One cannot draw a line through such a 

 curve, and say that all on one side of it are to be looked upon as 

 failures, on the other side as successes. To explain the curves, the 

 selectionists are thus obliged to admit that natural selection 

 shows its results in a continual and decreasing diminution of 

 numbers, as indeed one would to some extent expect from its 

 name. But if so, why did nature produce so many at first, only 

 to cut them down later, and where does the increase in number 

 come from, that is undoubtedly shown by the vegetable king- 

 dom? Was there no selection in ancient times? Differentiation, 

 on the other hand, as Yule has shown (75), necessarily results in 



