ARE VARIATIONS IN PARENTS TRANSMITTED TO OFFSPRING? (XXXIII-2)

The problem. It is a matter of common observation that the young of one generation bear more or less resemblance to the parents, but also that they differ from the parents. Interesting studies have been made in the effort to cause these differences from generation to generation to develop along the line of certain specially desired qualities.

What to use. The table given on page 174 shows the height of 928 persons whose records were studied by Sir Francis Galton. It is so arranged that the heights of these individuals may be compared with the heights of their parents and the inheritance of stature may thus be seen.

What to do. 1. In the third horizontal space from the top the figure given indicates the size-groups in which the children are classified. The vertical column at the left (column 1) gives the heights of the parents, the heading "Mid-Parental Height" meaning the middle point between the heights of two parents in a family. In column 16 at the right the figures in each space represent the average height of all children of parents of the heights indicated in the corresponding space in column 1. The other figures of the table indicate the distribution of the children. The way in which the table is read is indicated by the following examples:

2. Column 3 shows that among the seven persons whose heights were near 62.2 inches there are three from families in which the mid-parental height was 67.5; three from families with a parental average of 66.5; and one from a family in which the parental average was 64.5.

3. Line 6 shows that in all the families in which the midparental height was 72.5 inches one child had a height, when adult, of about 68.2 inches; two were 69.2 inches tall; one was

70.2; two were 71.2; seven belonged to the 72.2 group; two belonged to the 73.2 group; and four were taller than any of these.

4. Examine line f. Observe and state how wide is the variation. Note how many children are taller than their parents, how

MIDPARENTAL HEIGHT

HEIGHTS OF ADULT CHILDREN

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1

61.2

74.2 and 62.2 63.2 64.2 65.2 66.2 67.2 68.2 69.2 70.2 71.2 72.2 73.2 and OF CHILbelow

MEAN

above DREN

many are shorter, and how many are nearly of the parental height. Do you find that many of the children closely resemble the parents in height? Before you draw any conclusions study the lines c and j, and other lines, to see whether the relations you find in line f are generally true.

Questions. So far as you can determine by this study, what do you think about the probable average resemblance of a child to its parents? What are your conclusions about the likeness of the offspring to the parents?

Suggestions for report. The results of the observations called for under "What to do" should be recorded in your notebook. Reference work. Read sections 400 to 406.

Optional problems. Compare the average heights of parents (column 1, b to j) with the average heights of their children (column 16). Find the difference between these figures in each horizontal line, marking the differences by the plus sign (+) if the children average taller than their parents, and by the minus sign (-) if they are shorter. Are the children of unusually tall parents, on the average, taller or shorter than their parents? Are children of unusually tall parents taller than the average of all children? Are any of them taller than their parents? Make the same study regarding the unusually short persons. In general, do the children of unusual parents average as unusual as the parents? If the rule of inheritance shown above holds good for such characteristics as mental ability, moral tendencies, tendencies toward insanity and feeble-mindedness, what is the advantage of being "well-born"?

APPENDIX

I. SUGGESTIONS FOR THE USE OF GLASSWARE,

CHEMICALS, AND THE METRIC SYSTEM

NOTE. These directions are written to accompany the various pages of this manual as indicated in the notes below. The suggestions and tables appear in the order in which they will be needed in the problems as outlined.

NOTE 1 (p. 1). How to break (cut) glass. Ordinary glass tubing having a diameter of one-half inch or less may be cut as follows: Place the glass tube on the table and make a small notch at the desired point with the sharp corner of a triangular file. Next hold the tube in the hands with the thumb nails on the tube opposite the scratch. Pull on the tube and push with the thumbs. If the tube does not break easily make the notch deeper and longer.

NOTE 2 (p. 1). The glass plug. Secure a six-inch piece of glass tubing (Fig. 47, A) having an outside diameter of one fourth of an inch. Hold one end in the lower edge of the flame (Bunsen burner or suitable alcohol burner), rotate it slowly, and gradually bring the tube to the top of the flame. The pupil must remember that all glassware must be heated slowly and uniformly in order to prevent breakage. When the sharp edges of the tube become smooth (do not heat the glass until the hole is sealed) remove the tube, then treat the other end in the

same manner.

When the tube has cooled, hold the ends between the thumbs and fingers and place the middle of the tube in the lower part of the flame; rotate the tube; move it back and forth in the flame; and gradually bring it to the upper part of the flame. Continue the rotation, and heat about one inch of the tube uniformly until it becomes soft (do not let it bend in the flame); then remove it from the flame and immediately pull the ends apart (Fig. 47, B) until the middle portion contracts to a diameter of approximately an eighth of an inch. Allow the tube to cool. Cut the tube in the middle of the narrow portion. Save one part for a jet tube (Fig. 47, C') and make a glass plug (Fig. 1) of the other.