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Full text of "Man In The Modern World"

DARWINISM TO-DAY
better than others. Accordingly protective resemblance, as, for in-
stance, of the famous Kallima to a dead leaf complete with imitation
veins and mould-spots, may be pushed to an incredibly high pitch,
and yet have no effect on the survival of the species as a whole, which
will be decided mainly by the capacity of the caterpillars to survive
their much more numerous dangers.
Other examples of such "hypertelic" adaptations are seen in the
leaf-fish, which drifts up to within reach of its prey under the guise
of a floating dead leaf; the sea-horse of the Sargasso Sea, which
resembles a bit of Sargasso weed; or the extraordinary plant-bug
Heteronotus, which carries about an imitation ant on its upper surface
to scare off its enemies.
This intra-specific competition is most obvious when rival males com-
pete for mates, and most acute when polygamy prevails and success
in reproduction thus brings a multiple advantage. When this is so,
the characters which bring success in mating may become so over-
developed as to embarrass their possessors in the struggle for mere
existence, as with the train of the peacock or the wings—almost use-
less for flight—of the argus pheasant. Sexual selection here has bene-
fited none but certain types of males as against others: its results for
the species as a whole are harmful.
This distinction, it is clear, has great importance for human affairs.
Apologists for the laisser-faire system on the one hand and for mili-
tarism on the other hand, appealed to the Darwinian struggle for
existence as a justification. Now we realize that these forms of the
struggle, far from being helpful, are cither useless, in which case they
will be also wasteful, or actually inimical to progress.
Space forbids more than the barest mention of the ways in which
studies on development have illuminated some of the dark places of
evolution, I will confine myself to two examples. The antlers of a
stag, like the jaws of a male stag-beetle and many other masculine
characteristics, increase disproportionately with the increase in the
adult size of the animal. In a small stag, the antlers average about
2 per cent, of his total weight. But in a large stag weighing twice
as much, the antlers average almost 4 per cent.—while the body
has doubled its weight, they have quadrupled theirs.
If now during the evolution of deer, selection takes place for in-
creased bulk, there will be an automatic tendency for the antlers to
increase in relative size (a conclusion borne out in general by the
relative weight of antlers in species of deer of different sizes). Selection
may also operate directly on antler-size, but so far as our automatic
tendency is operative, change in relative antler-size is a mere by-
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