262 Evolution and Adaptation 
If the line is more carefully examined, it will be found that 
somewhere near the middle the men are much more nearly 
of the same height, or rather there are more men having 
about the same height than there are near the ends of the 
line. Another arrangement will bring this out better. If we 
stand in a line all the men from 60 to 61.9 inches, and in an- 
other parallel line all those between 62 and 63.9, then those 
between 64 and 65.9, then between 66 and 67.9 inches in 
height, etc., it will be found that there are more men in some 
of these lines than in others. The longest line will be that 
containing the men of about 65 inches; the two lines formed 
out of men on each side of this one will contain somewhat 
fewer men, and the next ones fewer still, and soon. If we 
looked at our new group of men from above, we should have 
a figure triangular in outline, the so-called frequency polygon, 
Figure 3 B. With a larger amount of data of this sort it is 
possible to construct a curve, the curve of frequency, Figure 
3 A. In order to obtain this curve of frequency, it is of 
course not necessary to actually put the individuals in line, 
but the curve can be drawn on paper from the measurements. 
We sort out the measurements into classes as in the case 
given above. The classes are laid off at regular intervals 
along a base-line by placing points at definite intervals. 
Perpendiculars are then erected at each point, the height of 
each being proportional to the frequency with which each 
class occurs. If now we join the tops of these perpendiculars, 
the curve of frequency is the result. 
“Jn arranging the individuals it will be found, as has been 
said, that certain groups contain more individuals. They 
will form the longest line. This value that occurs with the 
greatest frequency is called the mode. The position of this 
modal class in the polygon is one of the points of importance, 
and the spread of the polygon at its base is another. A 
polygon with a low mode and a broad range means great 
variability. The range may, however, be much affected by a 
