The growth of social forms is for the most part roughly analogous to that of the wild-grape vine which has extended itself over trellises and fences and into trees in my back yard. This vine has received from its ancestry a certain system of tendencies. There is, for example, the vital impulse itself, the general bent to grow. Then there is its habit of sending out straight, rapidly growing shoots with two-branched tendrils at the end. These tendrils revolve slowly through the air, and when one touches an obstacle, as a wire or branch, it hooks itself about it and draws up in the form of a spiral spring, pulling the shoot up after it. A shoot which thus gets a hold grows rapidly and sends out more tendrils; if it fails to get a hold it by and by sags down and ceases to grow. Thus it feels its way and has a system of behavior which insures its growth along the line of successful experiment. So in the human world we find that forms of life tending to act in certain ways come into contact with situations which stimulate some of their activities and repress others. Those that are stimulated increase, this increase acts upon the structures involved in it—usually to augment their growth—and so a “selective” development is set in motion. Intelligence may have a part in this or it may not; nothing is essential but active tendencies and conditions which guide their operation. You may sometimes see one vine growing upon another, involving the mutual adaptation of two living forms. In human life this is the usual condition, the environment being not something fixed but another plastic organism, interacting in turn with still other organisms, giving rise to an endless system of reciprocal growth. One form of life feels about among the various openings or stimuli offered by another, and responds to those which are most congruous with its own tendencies. The two experiment with each other and discover and develop some way, more or less congenial, of getting along. This is evidently true of persons, and the principle applies equally to groups, ideas, and institutions.