1897] REPRODUCTIVE DIVERGENCE 407 



of the race into two distinct races more and more obvious. Again, 

 I had supposed that the more widely any two individuals differed, 

 the less on an average would lie their mutual fertility. Hence this 

 principle of reproductive divergence is a cumulative one, and the 

 later stages of divergence will be very much more rapid than the 

 initial ones. 



Again, Dr -Jordan objects to my statement that as the race 

 diverges, shorter and longer individuals than those originally present 

 will gradually be evolved. This seems to me to be so obvious as to 

 scarcely need demonstration. Thus, let us suppose for the moment 

 that our 900 individuals of each sex are split up into 450 short 

 individuals and 450 tall ones. The members of each of these 

 groups will deviate in either direction from the average size in the 

 same proportion as the members of the original single group did. 

 For instance, in the 928 adult offspring obtained in the above- 

 mentioned anthropometric data, the mid-stature or median of the 

 whole group was about 68*2 inches, and 10 per cent, of the group 

 were below G4 - 5 inches in height. Supposing now the median of 

 the new group of short individuals be 6 5 "8 inches, it follows that 

 10 per cent, of this group will be below 62 - 2 inches in height. 

 That is to say, individuals shorter than any of those originally 

 present will have arisen. The tall individuals will, of course, 

 deviate in a similar manner in the opposite direction. 



This fresh attempt to demonstrate the correctness of the prin- 

 ciple of reproductive divergence will not, I am afraid, appear much 

 more easy to understand than the former one, but it at least has 

 the merit of being roughly founded on actual data, so that fewer 

 preliminary assumptions are necessary, and the result obtained is a 

 more absolute one, and is moreover independent of the Law of 

 Regression towards mediocrity. 1 To me it seems the principle is 

 sufficiently obvious without the help of any mathematics at all, if 

 it be looked at in the following manner. Let any number of 

 individuals in a species be divided up into two groups — the larger 

 ones and the smaller. Then if there be a correlation between size 

 and fertility, it follows that those larger individuals which happen 

 to breed with the smaller ones will give rise to fewer individuals of 

 intermediate size than they would have done if there had been no 

 such correlation. That is to say, the race will begin to diverge, 

 and as this divergence is cumulative, it will ultimately split up into 

 two or more new races. H. M. Vernon. 



1 •' Natural Inheritance," p. 95. 



