176 



HEREDITY AND VARIATION 



Problem 151 : To show variation in a given class. 



Materials. — Figures on pages 174, 175. Later the measure- 

 ments of the individual boys or girls of a class. 



a. Variation in Height 



Method and Observations. — tJsing the figures on pages 174, 175 

 have the members of the class place on graph paper a dot for 



each boy seen in the 



Number of 'E>oy 



133456789 10111213141516171819 20 2122233423 



510 

 59 

 58 



5-7 

 5.6 

 55 

 J.4 

 i3 

 S.X 

 S.l 

 5o 

 4U 

 4.10 

 4 9 



4.7 

 46 



plate, taking them in 

 numerical order. 

 Connect the points 

 made. Notice the 

 irregularity of the hne 

 formed. 



Now rearrange the 

 boys so that the tall- 

 est is at one end of 

 the hne and the short- 

 est at the other end, 

 with those of various 

 heights graded in be- 

 tween. Place dots on graph paper as in previous exercise. What 

 difference do you notice in the line made? The accompanying 

 graph shows the variation in height of the boys. 



But these boys differ slightly in mentality, considerably in 

 height, considerably in weight. Is there any relation between the 

 height and weight in a given group of boys ? 



NOTE. — In the following figure the line xy represents the normal curve of 

 weight and height relation obtained by weighing and measuring thousands of boys. 



14 9 15 8 S 6 17 a 3 7 Ifi la IB 4 2 23 lo 19 U 22 2524 20 1 13 



Bov'.s rearrctivgecl 



lov; 



b. To Form a Curve Showing the Relation of Weight to Height 

 in a Given Class 



Method. — Notice that a boy of 4 feet 5 inches should weigh 

 65 pounds, while a boy 5 feet 11 inches should weigh 170 pounds. 

 Knowing your own height, note what your weight should be. 



