The
arrangement of homogeneous objects of any kind in such form as this is
the first step in the study of variation by modern statistical methods,
and on such study much of the progress of genetics depends.]
[Illustration: FIG. 15.--Height is one of the stock examples of
a continuous character--one of which all grades can be found. As will be
seen from the above diagram, every height from considerably under five
feet to considerably over six feet can be found in the army, but extreme
deviations are relatively rare in proportion to the amount of deviation.
The vertical columns represent the total number of individuals of a
given height in inches. From Davenport.]
If a group of soldiers be measured as the children were measured for
arithmetical ability, their height will be distributed in this same
curve of probability. Fig. 14 shows the cadets of Connecticut
Agricultural College; it is obvious that a line drawn along the tops
of the files would again make the step-pyramid shown in Figures 10, 11
and 13. If a larger number were taken, the steps would disappear and
give place to a smooth curve; the fact is well shown in a graph for the
heights of recruits to the American Army (Fig. 15).
The investigation in this direction need not be pursued any farther.
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