Skip to main content

Full text of "Man In The Modern World"

See other formats

can secure a harem. They show olF (heir gorgeous plumage before
the hen birds in an elaborate and very striking display, at definite
assembly grounds where males and females go for (ho purpose of
finding mates. The old idea that the hen deliberately selects the
male she thinks the most, beautiful is putting the matter in human
terms which certainly do not apply to a bird's mind; but it seems
certain that the brilliant and exciting display does have an effect on
the hen bird, stimulating her to greater readiness to mate, Individual
male birds meet with different degrees of sueeess in this polygamous
love business: some secure quite a number of mates, others only one
or a few, and some get none at all. This puts an enormous biological
premium on success: the really successful male leaves many times
more descendants than the; unsuccessful. Here, then, is Natural
Selection working at an exceedingly high pitch of intensity to make
the display plumage and display actions more elleclive in their busi-
ness of stimulating the hens. Accordingly, in polygamous birds of
this kind, we often find the display plumage developed to a fantastic
extent, even so far as to be a handicap to the species as a whole.
Thus the display organ of the peacock, his train of enormously over-
grown tail-covert feathers, is so long and cumbersome that it is a
real handicap in flight. In the argus pheasant the chief display
organs are the beautifully adorned wings which the nude throws up
and forward in display so that he looks like a gigantic bell-shaped
flower. The business of display has been so important that it has
overridden the business of Hying, and now the malt* argus pheasant
can fly only with difficulty, a few feet at a time.
Here are two good examples of how u purely iutni-specifie struggle,
in this case between individual rival males-, can produce results which
arc not merely useless but harmful to the species as a whole in its
struggle for existence against its enemies and the forces of nature.
In general, selection for success in reproduction reaches greater in-
tensities than selection for individual survival, for the simple reason
that reproduction implies multiplication: the individual is a single
unit, but, as we have just seen for polygamous birds, success in re-
production may give the individual's characteristics a multiple repre-
sentation in later generations.
In flowering plants, the intra-speeific struggle for reproduction
between different individuals often produces results which, if not
directly harmful to the species, are at least incredibly wasteful We
need only think of the fantastic profusion of bloom on flowering trees
like dogwood or hawthorn or catalpa, or the still more fantastic pro-
fusion of pollen in trees which rely on fertilisation by the wind, like