es
manifest no inclination to live in society, that the instinct never has
played any part in their lives? Or because the primary purpose has
lapsed, does it follow that the secondary no longer exists?

Let me recapitulate the principal considerations which I have discussed
in this chapter.

Though I have been advancing a theory, and though I have taken much for
granted, yet it will, I think, be admitted that both the theory and what
has been taken for granted rest on observational grounds. As our
starting-point we have a bird whose inherited nature alternates
according to the season, and in whose nature we can distinguish two
contra-phases--the one to live in society, the other to live solitary.
While both have their part to play in furthering the life of the
individual, for biological interpretation there is only one end, the
prospective value of which is the continuance of the race. We may say
that the latter phase is the more important of the two because it is
directly concerned with reproduction. But we shall make a great mistake
if we attach peculiar importance to one phase, or to one mode of
behaviour within that phase, or to one action within that mode of
behaviour; for if there is one thing certain it is that the whole is an
inter-related whole in which each part depends for its success upon that
which precedes it.

In that phase in which the territory is the central feature of the
situation, the struggle for existence is in operation in its acutest
form; all the congenital and acquired capacities of the bird--pugnacity,
song, capacity to utilise in later phases the experience gained in prior
phases, all these are organised to subserve an end--a proximate
end--which in its simplest terms may be described as "isolation."
Isolation is then the first step in the process of reproduction, and any
individual that fails to make it good, fails to procreate its kind. But
isolation implies separation, and the degree of separation varies in
different species, from the few square feet of cliff required by the
Guillemot to the few square miles of barren moor over which the
Peregrine exercises dominion. One species must occupy sufficient ground
to enable it to secure food for its young; another requires sufficient,
but no more, upon which to deposit its egg; and a third must secure a
position for its nest within the community. Hence it follows that the
degree of separation varies with the conditions of existence. Since,