520 SOCIAL ASPECTS OF BIOLOGICAL RESULTS 



variations are due to the combined action of many small and 

 different causes. Human variations, whether bodily or mental, 

 may be registered on a curve of frequency, just like the varia- 

 tions of poppies or jelly-fishes — on the same sort of curve as may 

 be illustrated by plotting out the marks round the bull's-eye 

 in target practice, or the numbers which come to the top 

 in so many thousand throws of the dice, or the marks in a 

 competitive examination with a large number of candidates. 



Let us briefly recall Mr. Galton's argument. If we take a 

 precisely measurable quality like stature, we find that the 

 average height of a large number of adult Britons is 5 feet 8 

 inches ; above this line of mediocrity (R) there are taller men 

 who may be arranged in groups, the means of which are sepa- 

 rated from one another, by i| inches; we may call these +S, 

 + T, U, +V, +W, and +X, till we end in giants of 6 feet 

 6 inches ; we may give to the distance between the groups 

 (i| inches) the name " normal talent." Thus while the average 

 adult has 39 " normal talents " of stature (5 feet 8 inches), the six 

 groups above him, rapidly decreasing in numerical strength as 

 we ascend, have respectively i — 6 talents more than mediocrity. 



On the other side of mediocrity, there are of course groups of 

 minus variations, groups which we may call — s, — t, — u, 

 —V, — w, and — x, with i — 6 talents fewer than the normal 

 equipment of 39 ; and the minus or left side of the curve exactly 

 reflects the plus or right side. A giant of 6 feet 6 inches would 

 belong to the small and very select sixth class above medio- 

 crity (+X), while a dwarf of 4 feet 10 inches would belong to 

 the sixth class below par ( — x) ; and there are apparently as 

 many of the one as of the other. Mr. Galton maintains that 

 the curve holds good for any particular measurable quality 

 taken separately, and that it also holds good when the qualities 

 are grouped. " It can be employed to give a general idea of the 

 distribution of civilisation, in so far as it is normally distributed 

 . . . and the same for any group of normal qualities." 



