SECONDARY SEXUAL CHARACTERS 



123 



taken for granted that by selecting a particular kind 

 of individual the species will move in the direction 

 of selection. 



A few examples will bring the matter before us. If 

 we take a peck of beans and put all of those of one size 

 in one cylinder and those of other sizes in other cyl- 

 inders, and place the cylinders in a row, we get a result 

 like that in Fig. 61, A-E. If we imagine a line joining 



Fig. 62. — The normal binomial curve or the "ideal curve" of distribu- 

 tion. At the base line, the directions from the average value (o) are 

 indicated with the standard deviation (o") as unity. (After Johannsen.) 



the tops of the beans, the line gives a curve like that 

 shown in Fig. 62. This is known as the curve of prob- 

 ability. The curve can be, of course, most readily 

 made by making the measurements directly. Most 

 individuals of such a population will have the charac- 

 ter developed to the degree represented by the highest 

 point in the curve. Now if two individuals standing 

 at one side (let us say with the character in question 

 better developed than the average) become the parent 



