G NATURAL INHERITANCE. [chap. 



beings as the Father and the Mother '? How can we 

 appraise the hereditary contributions of different an- 

 cestors whether in this or in any other quality, unless 

 we take into account the sex of each ancestor, in addi- 

 tion to his or her characteristics ? Again, the same 

 group of progenitors transmits qualities in different 

 measure to the sons and to the daughters ; the sons 

 being on the whole, by virtue of their sex, stronger, 

 taller, hardier, less emotional, and so forth, than the 

 daughters. A serious complexity due to sexual differ- 

 ences seems to await us at every step when investigating 

 the problems of heredity. Fortunately we are able to 

 evade it altogether by using an artifice at the outset, else, 

 looking back as I now can, from the stage which the 

 reader will reach when he finishes this book, I hardly 

 know how we should have succeeded in making a 

 fair start. The artifice is never to deal with female 

 measures as they are observed, but always to employ 

 their male equivalents in the place of them. I trans- 

 mute all the observations of females before taking 

 them in hand, and thenceforward am able to deal 

 with them on equal terms with the observed male 

 values. For example : the statures of women bear to 

 those of men the proportion of about twelve to thir- 

 teen. 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. If the observed stature of a woman is 5 feet, 

 it will count by this rule as 5 feet + 5 inches ; if it be 



