selection. Such are the various sounds and
odours which are peculiar to the male, and which serve as a call to
the female or as an indication of his presence. These are evidently a
valuable addition to the means of recognition of the two sexes, and
are a further indication, that the pairing season has arrived; and the
production, intensification, and differentiation of these sounds and
odours are clearly within the power of natural selection. The same
remark will apply to the peculiar calls of birds, and even to the
singing of the males." Why the same remark should not apply to their
colours and adornments is not obvious. What is obvious is that "means
of recognition" and "indication that the pairing season has arrived"
are dependent on the perceptive powers of the female who recognises
and for whom the indication has meaning. The hypothesis of female
preference, stripped of the aesthetic surplusage which is
psychologically both unnecessary and unproven, is really only
different in degree from that which Mr. Wallace admits in principle
when he says that it is probable that the female is pleased or excited
by the display.

Let us for our present purpose leave on one side and regard as _sub
judice_ the question whether the specific details of secondary sexual
characters are the outcome of female choice. For us the question is
whether certain psychological accompaniments of the pairing situation
have influenced the course of evolution and whether these
psychological accompaniments are themselves the outcome of evolution.
As a matter of observation, specially differentiated modes of
behaviour, often very elaborate, frequently requiring highly developed
skill, and apparently highly charged with emotional tone, are the
precursors of pairing. They are generally confined to the males, whose
fierce combats during the period of sexual activity are part of the
emotional manifestation. It is inconceivable that they have no
biological meaning; and it is difficult to conceive that they have any
other biological end than to evoke in the generally more passive
female the pairing impulse. They, are based on instinctive foundations
ingrained in the nervous constitution through natural (or may we not
say sexual?) selection in virtue of their profound utility. They are
called into play by a specialised presentation such as the sight or
the scent of the female at, or a little in advance of, a critical
period of the physiological rhythm. T