575.8 45 



Reproductive Divergence not a Factor in the 

 Evolution of New Species 



AS it is of fundamental importance to know whether a species 

 can split up into two or more new species in one and the 

 same locality without the aid of any kind of local separation, or 

 whether isolation of some kind is a conditio sine qua 7ion, I ask 

 leave to reply to Mr Vernon's article in tlie last issue of Natural 

 Science, in which he tries again to demonstrate mathematically the 

 correctness of his theory of Eeproductive Divergence. For the sake 

 of argument and brevity I accept Mr Vernon's figures as being 

 correct, as I did in Natural Science, \o\. XI., p. 317. Then we have 

 as the result of the chance intermarrying of 900 parents under 

 ordinary circumstances the following number of ofi'spring (of each 

 sex) : 



, f a. Parents, oOO short, 800 medium, 300 tall =900. 

 \h. Ofrspring, 293 „ 314 „ 293 „ =900. 



If now the fertility of parents of the same size is assumed to be 

 higher than that of parents of different size, the figures are accord- 

 ing to Mr Vernon, as follows : 



J a. Parents, 800 short, 300 medium, 300 tall =900. 

 I &. Offspring, 300-6 „ 818-8 „ 300-6 „ =920. 



By a comparison of the offspring II. h. with the offspring I. h., 

 which, however, have nothing to do with one another, the individuals 

 under I. being physiologically different from those under II., Mr 

 Vernon comes to the conclusion that " short and tall individuals 

 have increased by 2-59 per cent., but the intermediate ones 

 only by 1-52 per cent." It is obvious that the figures under 

 II. 6. can only be compared with those under I. h. after the total 

 of II, h., which amounts to 920, has been reduced to 900. But 

 that is a mere oversight in the manipulation of the figures and of 

 no great importance, though the figures will, after the reduction, be 

 very different from what they are now. The grave error in Mr 

 Vernon's interpretation of the figures lies in the sentence following 

 the one quoted before: "There is thus a gain of about 1-0 7 per 

 cent, in favour of the extreme individuals over the intermediate 



