diesem Thier bemerkt hatte. Beim Anblick dieses Gegenstandes erregte
sich das Mannchen sichtlich, denn es polterte heftig an den Staben,
ebenfalls gurgelnde Laute ausstossend. As all the monkeys which have
the hinder parts of their bodies more or less brightly coloured live,
according to Von Fischer, in open rocky places, he thinks that these
colours serve to render one sex conspicuous at a distance to the other;
but, as monkeys are such gregarious animals, I should have thought that
there was no need for the sexes to recognise each other at a distance.
It seems to me more probable that the bright colours, whether on the
face or hinder end, or, as in the mandrill, on both, serve as a sexual
ornament and attraction. Anyhow, as we now know that monkeys have the
habit of turning their hinder ends towards other monkeys, it ceases to
be at all surprising that it should have been this part of their bodies
which has been more or less decorated. The fact that it is only the
monkeys thus characterised which, as far as at present known, act in
this manner as a greeting towards other monkeys renders it doubtful
whether the habit was first acquired from some independent cause, and
that afterwards the parts in question were coloured as a sexual
ornament; or whether the colouring and the habit of turning round were
first acquired through variation and sexual selection, and that
afterwards the habit was retained as a sign of pleasure or as a
greeting, through the principle of inherited association. This
principle apparently comes into play on many occasions: thus it is
generally admitted that the songs of birds serve mainly as an
attraction during the season of love, and that the leks, or great
congregations of the black-grouse, are connected with their courtship;
but the habit of singing has been retained by some birds when they feel
happy, for instance by the common robin, and the habit of congregating
has been retained by the black-grouse during other seasons of the year.
I beg leave to refer to one other point in relation to sexual
selection. It has been objected that this form of selection, as far as
the ornaments of the males are concerned, implies that all females
within the same district must possess and exercise exactly the same
taste. It should, however, be observed, in the first place, that
although the range of variation of a species may be very large, it is
by no means indefinite. I have elsewhere given a good instance of this
fact in the pigeon, of which there are at least a hundred varieties
differing widely in their colours, and at least a score of varieties of
the fowl differing in the same kind of way; but the range of colour in
649