Evening star., 1932-03-21

survival through natural selection-a
corner stone Of the philosophy of older
evolutionists-arec called into question in
an extensive study, based largely on the
contents of birds stomachs, announced
yesterday by the Smithsonian Institu-
ton
Insects are eaten by other animals
in proportion to their abundance, ac-
cording to the results Of this study, and
the effect of natural enemies upon them
is fndiscriminate. the study concludes.
The enormous variety of supposedly
defensive mechanisms scattered through
nature-inimicry Of dangerous species
by weak species, offensive odors, poi
sonous secretions, hard shells, warning
colors, frightful appearances and the
rest-apparently are Of little value to
their possessors. All have some weak
link In their defenses and are eaten.
The generally accepted evolutionary
theory has been that when an animal
possessed some advantageous trait. such
as colorfng which rendered it practi-
cally invisible against its environment,
it was less likely to be eaten than
creature of the same species without
this advantage. Consequently, it was
more likely to survive and transmit the
advantageous factor to its progeny.
Thus the factor that made for the
greatest security would become fixed in
q race.
Study Includes All Groups.
This theory does not check altogether
with the facts as to the feeding habits
of birds, as gathered for the Smith
logical Survey. McAtee deals chiefly
ipc ciyano ithaca ro thn chief
articles of diet Of many birds and can
be identified in their stomachs He
extends his observations through the
fish, bird, amphibian, reptile and man.
NAL groups.
Probably no living creature, he finds.
Is immune from serving as some other
creatures dinner The total mortality
of animal groups he concludes, is In
strict proportion to their numbers. A
pair of the new generation remains, to
replace a pair of the old, and apparent
elimination of all but that pair Is very
largely due to agencies indiscriminate
in their action. There would seem
to be no discriminative eliminating
forces of sufficient strength to bear the
very great burden put upon them by
natural selection theories" he con-
cludes.
MChIcC ODScI FdIlOllo lLlCluOC oOAAN "a
the most striking instances OF supposed
protective mechanisms in nature. None OF
them enables an insect family to escape
its normal death rate. Otherwise, the
reproductive powers of most insects be-
ing so great, highly protected family
soon might overrun the earth.
Some of the most notable cases OF
the failure Of supposedly protective de-
vices to safeguard insects, summarized
by McAtee, are among the following:
Demonic Aspect Fails.
The dragon fly is a demonic creature:
It's big head seems to consist Chiefly oil
two enormous eyes. Some kinds have
a vivid. fear inspiring color pattern
with vivid spots of green, yellow, red
and blue on a dark background. lint
crate people often hold the insect In
superstitious awe. 1t is one OF the
swiftest flyers in the animal kingdom.
Quite in contrast to this flying demon
is its close relative, the damsel fly. This
insect generally is weak flyer, and
some Of its species are dull colored. 1t
is of a slighter and more delicate struc-
ture. Yet. 1t Is shown by examination
of the bird stomachS, apparently
strength and fearsomeneSs are OF little
protective value of the dragon f1y. Both
dragon flies and damsel flies are eaten
in proportion to their abundance. not
in proportion to the development OF
their supposedly protective mecna-
nisms. There is high mortality IN
both races due to cannibalism. Inc
immature stages OF both lack tne pro,
tective devices of the adults and ian
easv victims to frogs, turtles and hsh.
The adult dragon fly has no terrors ior
ants. spiders, robber flies, chipmunks,
snakes, frogs and toads.
A striking example Is afforded by the
termites. They pass most OF their nVes
concealed from their enemies In gal
leries in wood or underground or In
we'll built nests. They have soldier
caste" we'll armed With strong jaws.
They emit corrosive secretion. some
of them have warning colors. Yet
enormous numbers of them fall prey to
birds They are even eaten by man.
Frogs, rats, jackals, mongooses, jungle
cats, dogs. lizards, spiders ana ants de-
YOUR them. Their protective mechan-
isms appear to be failures. put. tne
study shows, they are not eaten out OF
proportion to their abundance.
Deception Proves Futile.
The ''walkingstick" family, according
tn the protectionist theory, has reached
the acme of protective mimicry. Vari-
ols species look like sticks, stems OF
grass. bits of moss or pieces of lichen-
colored bark. Some are covered with
strong spines, like thorns. Yet, McAtee
points out, many of them are eaten by
birds. and their sluggishness makes
enormous numbers of them victims of
grazing animals whose huge mouths
engulf indiscriminately great quantities
of grass and insects.
Most members Of the great insect
Iocusts and crickets are supposedly
protected by colors almost indistin-
g,iishable from the background OF soil
or vegetation This coloration includes
a great variety of earth tints, rock and
sand texture, the browns, greens and
grays of living and dead vegetation, to-
gether with appropriate mixtures Of yel-
low, orange, rose and silvery white. The
wing covers of certain katydids look
like leaves So close is the imitation
that there are markings like the spots
on leaves due to fungi or the tracks Of
leaf-mining insects. Some of them are
most remarkable leapers. Some mimic
other insects, such as ants and beetles.
Yet, McAtee finds. these devices are OF
little avail. Nearly a tenth of all the
achs are Of this family. They consti-
tute a staple bird food. Some Of the
most effectively colored, from a pro-
tectionist standpoint, are among the
most commonly eaten.
Col0ring Examples Cited.
The moths and butterflies, some Of
whom have carried mimicry to an eX-
treme stage, seem to fare no better. The
larvae of some species, helpless and de-
fanseless, look like the feared hornets
and wasps. The majority of adults
have what is known as cryptic color
ation," resembling details Of the en-
vironment, so that they are inconspicu-
GUS on bark and old leaves. A notable
example is that of the stick caterpil-
lar" rarely seen because of their per-
feet resemblance to the twigs Of plants
on which they feed One caterpillar is
in color an exact co,lnterD3rt of a rough