PLANT HYBRIDIZATION BEFORE MENDEL 247 



ton states his reasons for selecting it as a subject for the investi- 

 gation of heredity. 



"Some of its merits are obvious enough, such as the ease and frequency 

 with which it may be measured, its practical constancy during thirty-five 

 or forty years of middle life, its comparatively small dependence upon 

 differences of bringing up, and its inconsiderable influence on the rate 

 of mortality." (p. 83.) 



"other advantages not equally obvious are equally great. One of these 

 is the fact that human stature is not a simple element but a sum of the 

 accumulated lengths or thicknesses of more than a hundred bodily parts." 

 (pp. 83-4.) 



"The beautiful regularity in the Statures of a population, whenever 

 they are statistically marshalled in the order of their heights, is due to 

 the number of variable and quasi-independent elements of which Stature 

 is the sum." (p. 85.) 



The data for stature and the other human characters observed 

 were obtained from the "Records of Family Faculties," amounting 

 to 150 families in all, from which Galton extracted data as to the 

 stature of 205 couples of parents, as compared with a total of 

 930 of their adult children of both sexes. For purposes of calcula- 

 tion, Galton introduced the theoretical "mid-parent," 



". . . an ideal person of composite sex, whose Stature is halfway between 

 the Stature of the father and the transmuted Stature of the mother." 

 (p. 87.) 



The transmutation for female stature was stated as follows : 



"The artifice is never to deal with female measures as they are ob- 

 served, but always to employ their male equivalent in the place of them. 

 I transmute all the observations of females before taking them in hand, 

 and thenceforth am able to deal with them on equal terms with the ob- 

 served male values. For example : the statures of women bear to those 

 of men the proportion of about twelve to thirteen. Consequently by 

 adding to each observed female stature at the rate of one inch for every 

 foot, we are enabled to compare their statures, so increased and trans- 

 muted, with the observed statures of males on equal terms." {ib., p. 6.) 



As a result of these data, Galton concluded that: 



"The filial deviation from P (the mid-stature of the population, 68j^ 

 inches), is, on the average, only two-thirds as wide as the Mid-Parental 

 Deviation. I call this ratio of 2 to 3 the "ratio of 'Filial Regression.' It is 

 the proportion in which the Son is, on the average, less exceptional than 

 his Mid-Parent." (p. 97.) 



"This value of two-thirds will therefore be accepted as the amount of 

 regression, on the average in many cases, from the mid-parental to the 

 mid-filial stature whatever the mid-parental stature may be." (p. 98.) 



Galton discusses the practical effects of the law of regression 

 thus : 



