n close
proximity; so that if more than one community were to attempt to
establish itself in a limited area, the supply of food or the supply of
trees might become a pressing problem. Each community must therefore be
prepared to defend its own interests, and each must be regarded as one
unit and the area occupied as one territory within which are included a
number of lesser territories. The individual may fail to establish
itself within a community, but, even if it succeeds, the community may
fail to establish the rights of communal ownership; hence it has to face
a twofold possibility of failure, and if it lacked the inherited nature
which leads the Guillemot to secure a position upon the ledge, or the
Bunting to obtain a position in the marsh, the chances are that it would
fail in the attainment of reproduction.

The question now arises as to how it comes about that the area occupied
by each individual conforms in broad outline to that which has proved
beneficial for the welfare of the species as a whole. We shall find that
up to a point the answer is a simple one. No one could study the
behaviour of animals without observing the important part that habit
plays in the life of the individual; an action performed to-day is
liable to be repeated to-morrow and the following day until it becomes
ingrained in the life of the individual. This must not be taken to mean,
however, that a particular action has to be performed for many days in
succession before it becomes definitely fixed; if only it is repeated a
number of times, even within the space of a few hours, it will acquire
sufficient strength for its continuance; but continued repetition gives
increased fixity, and, as time goes by, it becomes increasingly
difficult for the creature to make a change unless the character of the
situation necessitates readjustment.

For example, when the organic condition which leads to nest-building
becomes active, the bird tentatively collects some of the necessary
material in its bill, flies round with it, and then drops it. After a
while it collects some more, and this time leaves it perhaps in a bush.
Later on it makes another attempt, and, meeting with a situation which
calls forth the appropriate response, it thereupon lays the foundation
of the structure. We will assume that the nest is placed in the midst of
a tangled bush. Well, the bird lays the first strands of the foundation
and then goes in search of more material. The nex