18971 REPRODUCTIVE DIVERGENCE 405 



The fresh example I propose to adduce is founded on actual data, 

 namely, the measurements of human stature in the case of parents 

 and their offspring, which are given by Galton in his work on 

 "Natural Inheritance" (p. 208). Here the relations between 

 the stature of 205 'parents of each sex and of their adult 

 offspring are classified. The mid-parents 1 split up into three 

 nearly equal groups — viz., those below 6 7 "8 inches in stature, those 

 from GT'S to G9'2 inches, and those above 69'2 inches. These 

 groups were found to give rise to more or less equal numbers of 

 children. The numbers of children of each stature which were 

 given birth to by each of these three groups of short, medium and 

 tall mid-parents were then determined, partly by plotting out the 

 various numbers and calculating from the smoothed curves, and 

 partly by direct enumeration of the numbers. By then taking 

 means between the numbers of tall children produced by tall parents 

 with those of the short children produced by short ones, and also 

 between the numbers of short children produced by tall parents with 

 those of tall ones produced by short parents, roughly speaking the 

 following mean values were arrived at : — 



Short. 



100 short parents give . 54 



100 medium . . .31 



100 tall . . . 15 



100 100 100 



From these figures it is seen that the percentage numbers of children 

 are given, and not the actual numbers. This plan was adopted in 

 order that the numbers of children might be kept the same as that 

 of the parents. We see, therefore, that if 100 short, medium and 

 tall parents of each sex be taken, the numbers of short, medium and 

 tall children will still remain at 100, in spite of the fact that the 

 children of each group produced by the different parents vary from 

 15 per cent, to 54 per cent. 



In addition to the children produced by short, medium and tall 

 parents, it is for our purpose necessary to know the numbers pro- 

 duced by intermarriages of short and medium, and of medium and 

 tall parents. These numbers may be approximately obtained by 

 taking means between the percentages for short and medium parents 

 on the one hand and for medium and tall ones on the other. Thus : 



Short. Medium. Tall children. 



100 short and medium parents give 425 34'5 23 



100 medium and tall . . .23 345 42*5 



It is also necessary to assume, as Galton has shown his statistics 

 warrant us in doing, that short and tall and also tall and short 



