ters. The great difference between this and the earlier view
is that instead of allotting one factor to each character, students now
believe that each individual character of the organism is produced by
the action of an indefinitely large number of factors,[46] and they
have been further forced to adopt the belief that each individual
factor affects an indefinitely large number of characters, owing to the
physiological interrelations and correlations of every part of the body.

[Illustration: HOW DO YOU CLASP YOUR HANDS?

FIG. 16.--If the hands be clasped naturally with fingers
alternating, as shown in the above illustration, most people will put
the same thumb--either that of the right or that of the left
hand--uppermost every time. Frank E. Lutz showed (_American Naturalist_,
xliii) that the position assumed depends largely on heredity. When both
parents put the right thumb uppermost, about three-fourths of the
children were found to do the same. When both parents put the left thumb
uppermost, about three-fifths of the children did the same. No definite
ratios could be found from the various kinds of matings. Apparently the
manner of clasping hands has no connection with one's right-handedness
or left-handedness. It can hardly be due to imitation for the trait is
such a slight one that most people have not noticed it before their
attention is called to it by the geneticist. Furthermore, babies are
found almost always to clasp the hands in the same way every time. The
trait is a good illustration of the almost incredible minuteness with
which heredity enters into a man's make-up. Photograph by John Howard
Paine.]

The sweet pea offers a good illustration of the widespread effects which
may result from the change of a single factor. In addition to the
ordinary climbing vine, there is a dwarf variety, and the difference
between the two seems to be proved, by exhaustive experimental breeding,
to be due to only one inherited factor. Yet the action of this one
factor not only changes the height of the plant, but also results in
changes in color of foliage, length of internodes, size and arrangement
of flowers, time of opening of flowers, fertility and viability.

Again, a mutant stock in the fruit fly (Drosophila) has as its most
marked characteristic very short wings. "But the factor for rudimentary
wings also produces other effects as well. The females are almost
completely sterile, while the males are fertile. The via