1898] BEPRODUCTIVE DIVERGENCE 47 



sets of individuals have no advantage over each other in respect to 

 other factors. 



But the best test of the fallaciousness of the hypothesis we shall 

 have, when we accept Reproductive Divergence as a true factor, and 

 apply this factor again to the two races into which the original 

 species has developed by means of Reproductive Divergence. Let 

 us then suppose that the 900 individuals are split up into a race of 

 450 short and a race of 450 tall individuals. The mean of the 

 short race is "supposed" by Mr Vernon to be 65'8 inches — why 

 it must be 6 5 '8 inches I do not know. As "the members of this 

 group deviate in either direction (spaced type mine) from the 

 average size [6 5 "8 inches] in the same proportion as the members of 

 the original group did, it follows that 1 per cent, of this group will 

 be below 62-2 inches in height." Certainly; but the average size 

 being 6 5 "8 inches there will also be 10 per cent, above 69*4 inches 

 in height ! The members of the tall race will, of course, deviate in 

 a similar manner; the medium size of this race being 70 '6 inches 

 there will be 10 per cent, of the individuals below 67 inches. 

 Where is the gap between the two races? Let us, however, sup- 

 pose there be a gap between them and apply the principle of Re- 

 productive Divergence to the two now separate races. It is self- 

 evident that the short race will split up into a still shorter one and 

 into a taller one, and that the tall race will develop into a less tall 

 one and a more tall one, and so on. Will not the gap which 

 we assumed to exist between the above two races be filled up 

 now ? Reproductive Divergence itself will mend the gap which it 

 is claimed to tear into the evenly convex curve of a species. 



Kakl Jordan, 



Zoological Museum, Tring. 



