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Full text of "Man In The Modern World"


pine and fir. The individual trees are competing for the privilege of
surviving in their descendants; the species could certainly perpetu-
ate itself with a much more modest expenditure of living material.

One final example. Naturalists have often noted the almost un-
believable perfection of the protective resemblance of certain insects
to their surroundings. The most extraordinary cases are the re-
semblances of various butterflies, like the Kallima, to dead leaves.
Not only do the folded wings perfectly resemble a dead leaf in shape
and colour, not only do they have a projection to imitate the stalk,
and dark lines which perfectly simulate the veins, but some even go
so far as to be marked with imitation mould-spots and holes!

Now, in all butterflies the survival of the species depends to a
preponderant degree on the capacity of the defenceless and juicy
caterpillar and chrysalis to survive. Selection presses with much
greater intensity on the larval and pupal stages than on the adult.
Furthermore, there is some sort of balance between the number of
adults which survive to reproduce themselves and the intensity of
selection which presses on the next generation of caterpillars. If
more adults reproduce, there will be many more caterpillars, and
they will be more easily found by their enemies, especially the tiny
parasitic wasps which lay eggs inside the caterpillars, the eggs grow-
ing into grubs which devour the unfortunate animals from within.
Conversely, if fewer adults reproduce, there are many fewer cater-
pillars, but each of them has a better chance of surviving to the
butterfly stage. Accordingly, the protection of the adults is, from
the point of view of the species, a secondary matter. Of course they
must be protected sufficiently well for a reasonable number to survive
and reproduce, but after this it is quite unimportant—for the species—
if a slightly higher or a slightly lower proportion survives.

It is unimportant for the species but it remains important for the
individual. If one kind of adult is better protected than another, it
will automatically leave a higher average number of offspring; and
so the mtra-specific struggle for reproduction among the individual
adult butterflies will continue to push any protective devices they
possess'on toward ever greater efficiency, even though this may be
quite immaterial to the survival of the species. The perfection of the
kallima's resemblance to a dead leaf is one of the marvels of nature;
not the least marvellous part of it is that it is of no value to the species
as a whole.
On the other hand, intra-specific competition and struggle need
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