usefulness; and while, speaking generally,
this is a true statement of the case, there is much evidence to show
that the relationship between them is nevertheless very close. There
are, for example, quite a number of cases in which a particular
call-note is uttered with unusual energy during sexual emotion, and is
attached to the song, of which it may be said to form a part; but a
still closer connection can be traced in many simple melodies which are
merely compositions of social and family calls repeated many times in
succession, and even in some of the more complex productions there will
be found indications of a similar construction. And since this is so,
since moreover, in the seasonal vocal development of such a bird as the
Yellow Bunting, we can observe the gradual elaboration from simple to
complex--from the repetition of single notes to phrases and from phrases
to the complete melody--we have every reason to suppose that it is along
these lines that the evolution of the voice has proceeded.

In all probability there was a time when vocal expression was limited
to primitive social and family cries which would be called into play
with special force during times of excitement, more particularly during
the sexual season which is the period of maximum emotional excitement.
But the excitement would express itself in all the congenital modes of
behaviour peculiar to the season, and thus the repetition of these cries
would become associated with combat, with extravagant feats of flight,
and with other forms of motor response. Now the more emotional
individuals would be the more pugnacious, and all the more likely
therefore to secure territory and so to procreate their kind; and, being
of an excitable disposition, they would at the same time be the more
vociferous. Hence variations of the hereditary tendency to vocal
expression, even though in themselves they were not of survival value,
would be fostered and preserved, so long as they were not harmful, in
virtue of their association with pugnacity. But if, instead of being
neutral, they helped to further the biological end of combat, the
relationship between the voice and pugnacity would be of a mutually
beneficial kind; and those individuals in which variation in both
directions happened to coincide, would have a better chance of success
in the attainment of reproduction.

A territorial system, closely corresponding to that which we have
discussed, forms part of the l