hich song may have attained a fuller
development, and which would account in some measure for the
elaboration, inexplicable merely in terms of "recognition." It is this:
the effect of the sexual call upon the female cannot well be neutral, it
must be either pleasurable or the reverse--it must, that is to say, be
accompanied by some suggestiveness, and by suggestion I mean the
arousing of some emotion akin to that of the male; and if there are
degrees of suggestiveness, which well there may be, some males will mate
sooner than others and some will remain mateless--this is the theory of
sexual selection. The question to be decided here is whether the
biological emphasis is on loudness, or specific distinctness, or pitch,
or modulation, or the manner in which the phrases are combined--that is,
on some qualities in preference to others--or whether the emphasis is on
the whole. We have already seen, and it is well known, that there is
much variation in the voices of different individuals of the same
species, and thus the first condition of the theory is fulfilled. Now
the conditions which lead to variation are threefold--immaturity,
seasonal sexual development, and isolation. Of the three, the variation
in the case of the immature bird is the most instructive; the tone is
not so pure, the combination of phrases is incomplete, and elaboration
is imperfect, and yet, notwithstanding all these imperfections, we can
observe that the bird pairs as readily as does the adult. But even if we
lacked this demonstrative evidence, we should still be justified in
assuming that such must be the case, for we know from experience in the
preservation of game, where there is no surer way of reducing the stock
than by leaving too high a percentage of old cocks, that for the young
bird to be at any disadvantage in competition with the adult is
detrimental, if not disastrous, to the species. So that while there is
plenty of evidence of variation in those particular qualities which
appeal to our aesthetic faculties, there is at the same time evidence
which demonstrates that such variations exercise no influence on the
course of mating; and inasmuch as it is difficult to conceive of any
voice departing more from the normal type in these particular qualities
than the immature does from the adult, if there be degrees of
suggestive influence, we must seek it in some other direction. There
remain the two other characteristics which we found to be constan