Nov., 1895. 



THE ROLE OF SEX. 



343 



amend Quetelet's statements in one important particular. Wliile 

 Quetelet thought that we might represent by a simple symmetrical 



Fig. 2. — Weights of stones from 

 a beach. 



curve the qualities of a group of individuals called by us a "species," 

 Galton insists that free interbreeding between members of that group 

 is a necessary condition, without which the curve will not preserve 

 the same proportions. Now, free interbreeding does not occur 

 between different races, and as Galton remarks on p. 29, " it clearly 

 would not be proper to combine the heights of men belonging to two 

 dissimilar races in the expectation that the compound result would be 

 governed by the same constants." Venn^ illustrates this by an 

 attempt to mix the heights of the taller English with those of the 

 shorter French race. He says, " If we mix up the French and 

 English heights what will follow ? Beginning from the English 

 mean of 5 ft. 9 in. the heights will at first almost entirely follow the 

 law determined by the English conditions, for at this point the 

 English data are very numerous, and the French by comparison 

 very few. But as we begin to approach the French mean the 

 numbers will cease to show the continual diminution which they 

 should according to the English scale of arrangement, for here the 

 French data are in turn very numerous, and the English by com- 

 parison few." The result of such a combination of heterogeneous 

 elements is illustrated by Fig. 3 (of course in an exaggerated form.) 



F E 



Fig. 3.— French and English. Fig. 4.— Pugs and St. Bernards. 



More striking still would be the compound curve which would 

 result were the heights of the Bushmen and the Patagonians mixed 

 together, or even a more extreme example still, the heights of pugs 

 and St. Bernard dogs. Here we are dealing with two races or breeds 

 of the same species, with two groups of individuals which at one time 

 interbred, but which are now separated from each other, and as a 

 result of selection have become vastly different. In these cases the 

 two curves are not superimposed at all, but lie far apart, for the 

 largest pug is smaller than the smallest St. Bernard. (Fig. 4.) 



The simplicity and symmetry of the curve of any measurable 

 1 "Logic of Chance," 1S7G, p. 40. 



