HARMONIES AND DISHARMONIES AMONGST BEINGS INFERIOR TO MAN
The organised world before the appearance of man on the earth—Absence
of a law of universal progress—Fertilisation of vanilla—The part
played by insects in the fertilisation of orchids—Mechanism by which
insects carry the pollen of orchids—Habits of fossorial
wasps—Harmonies in nature—Useless organs—Rudiments of the pollinia of
orchids—Disharmonies in nature—Unadapted insects—Aberration of
instincts—Perversion of sexual instinct—Attraction of insects by
light—Luminous insects—Law of natural selection—Happiness and
unhappiness in the organised world
Long before man appeared on the earth animals and plants were
distributed over it. Some of these were endowed with but vague senses,
while others had well-developed instincts, and some even a certain
degree of intelligence which they applied for their self-preservation
and for the propagation of their own kind.
Many species, well adapted for the resistance of external influences,
have survived from very early times to the present day. In the
Carboniferous period birds and mammals did not yet exist, and the thick
forests, with undergrowths of gigantic ferns, were inhabited by large
numbers of articulated animals, amongst which were scorpions and
insects. The scorpions of that time resemble in every way those that
actually live at the present day in tropical countries; and amongst the
insects of that early epoch were some very like the cockroaches of
to-day. Certain tree-like ferns of the present time are also very
similar to those of the coal period. Amongst the animals the bodies of
which are protected by a shell, such as foraminifera and mollusca,
certain species have survived even from an earlier time than the coal
period.
In contrast with this extraordinary survival, there are instances of the
complete disappearance of numbers of species of animals and plants. In
early times, during the Tertiary epoch, the virgin forests of Europe
were inhabited by a large number of monkeys, of which fossil remains are
now found, especially in Greece. These formerly existed even in Europe,
and some anthropoid apes (_Dryopithecus_) have left traces in the
tertiary deposits of France.[28] These animals, notwithstanding that
their organisation was superior to that of scorpions and cockroaches,
have not been able to adapt themselves to the altered conditions of
modern Europe. A similar fate has come upon some of the higher mammals,
such as the mammoth and the mastodon.
These facts do not bear testimony to the prevalent idea that there
exists in nature a law of universal progress tending to the production
of organisms more and more perfect from the point of view of complexity
of structure. It is incontestable that forms higher in the scale of life
have developed only after the appearance of lower forms. But it does not
follow that development always takes a progressive march. Man is one of
the later species that have appeared upon the earth, but there are
others of still more recent date. It is very probable that certain
species of lice have appeared subsequent to man, particularly the
clothes-louse (_Pediculus vestimenti_). Amongst the true parasites which
live only in the human body are some that have acquired their specific
characters after the appearance of man. Such are certain tape-worms and
microbes, such as a species of _gonococcus_. It is therefore amongst
parasites and not to man that we must look for the latest products of
creation.
In nature, then, there is no blind tendency towards progress. Organisms
almost innumerable are born every day with variable characters. Those
amongst them which are adapted to existing circumstances survive and
produce offspring like themselves, but many do not reach maturity, and,
living only for a short time, die without leaving issue.
To give the reader a better idea of adaptations and of their importance
to living creatures, it will, perhaps, be as well to devote some space
to an account of examples of them. Amongst organisms that attract our
attention by their pleasing aspect, there are not many that can rival
flowering plants. Every one admires the great beauty of the blossom of
orchids. There can be no doubt that these flowers have not been
developed to satisfy the æsthetic tastes of man, for the simple reason
that orchids existed for a long time before man’s appearance.
Among orchids there is one which, for more than half a century, has been
cultivated by man in many tropical countries. This is the Vanilla, the
fruit of which produces one of the sweetest of spices.
In former days the pods of only the wild vanilla, which is an
undergrowth of the forests of Mexico and South America, were gathered.
But the employment of vanilla to flavour chocolate has rendered its
artificial culture lucrative; consequently the plant has been
transported to several warm countries where it could be acclimatised. It
has flourished and borne numerous blossoms, but it has never produced
fruit from which alone the aroma is obtained. As the question of the
sterility of the vanilla was of great practical interest to the
cultivator, the matter was investigated, and it was found that the
flower remained sterile because the female and male parts could not come
in contact. The pistils and stamens of the flower are well developed,
but between these sexual organs is a membrane which prevents
fertilisation. After this discovery was made, the idea occurred that the
pollen of the vanilla flower might be transferred artificially to the
stigma of the pistil so as to bring about “artificial” fertilisation. A
young black slave, Edmond Albius, a native of Réunion, discovered in
1841 a practical method by which the male and female elements of the
vanilla could be put in contact; and from this discovery there came a
great extension of the cultivation of the orchid in many countries. At a
certain period a small bamboo point or the tooth of a comb is introduced
into the vanilla flower, and in this way, in a short time, a quantity of
flowers may be fertilised and so made capable of bearing mature
pods.[29]
In the original home of the vanilla the intervention of man is
unnecessary. In Guiana and Mexico fertilisation of the flower is the
work of small bees (of the genus _Melipona_). They frequent the vanilla
flowers to extract nectar, the material of their honey. Small
humming-birds also hover over the vanilla blossoms, and by introducing
their bills into the sexual organs of the flowers bring about contact of
the male and female elements.
Sterility of the vanilla in the countries to which it has been
introduced, before the employment of artificial fecundation, is easily
explained by the fact that in these countries there are no insects nor
humming-birds capable of transporting the pollen.
But it is not only the vanilla that requires the co-operation of living
beings to produce its fruits. It is the case with many other orchids. In
the flowers of these the pollen is massed together and cannot be
transported by the air. It needs the aid of insects, as had already been
pointed out by Sprengell in the eighteenth century, and above all by
Darwin, whose splendid investigations are the basis of the following
passages.[30]
Insects, belonging to different groups, such as bees, wasps, flies,
certain beetles, and many butterflies and moths, visit orchids to sip
the nectar produced by the plants and stored in definite parts of the
flowers. In order that their proboscis may reach the stores of sweet
juice, the insects inevitably touch first the upper parts of the
flowers, where the anthers are present. The pollen grains are clustered
in masses, known as pollinia, and these adhere to the body of the
visiting insect by means of an adhesive fluid which is secreted by an
organ of the flower known as the _rostellum_. In this way the pollinia
adhere firmly, it may be to the proboscis of butterflies, or to the head
or any other part of the body of insects. They can leave the flower and
fly away without losing the adhering pollinia, and in this manner they
serve as the agents for sexual contact and for fertilisation of the
orchids. Ménière relates that a person who kept bees near the garden of
the Faculté de Toulouse complained that they returned from the garden
with their heads covered with tiny yellow bodies which he was unable to
clean off from them. It was easy to recognise in these bodies the
pollinia of orchids very firmly attached to the bees’ heads.[31]
When an insect, bearing these pollinia, introduces itself into another
flower of the same species of orchid, it inevitably comes in contact
with the female apparatus, more particularly with the viscous surface of
the stigma. Some of the grains of pollen contained in the pollen-mass
adhere to the stigma and are thus enabled to fertilise the ovule. This
carriage of pollen from one flower to another brings about a crossing
which is necessary for the production of good seed. On the other hand,
the seed which is the result of self-fertilisation of a flower is
inferior.
An examination of the structure and form of the flowers of many orchids
show that they are adapted in a truly marvellous way to the visits of
insects that convey pollen. In each part of these flowers one can
discern some useful arrangement to secure cross-fertilisation.
For the proper transmission of pollen it is necessary that the pollinia
should adhere very firmly to the body of the insects, and that the
viscous substance which holds them together should have time to
solidify. It is thus of great advantage to the plant if the insects
remain for a considerable time on the flower. In several orchids the
nectar is not easily accessible, and frequently the insect has to search
for a long time before finding what it desires, and sometimes it even
has to pierce a membranous covering before reaching the fluid. The
operation takes a certain time, and this is long enough to allow the
mucus by which the pollinia adhere to the insect to set firmly.
In the case of orchids the mucus of which sets instantaneously, there is
no reason for the visit of the insect to be prolonged. In such cases the
nectar is easy to extract, and the insect finds it without loss of time.
Darwin, after describing these facts, proceeds to say:[32]
“In these five species” (in which the viscid matter “is so adhesive that
it serves to attach the pollinia firmly to the insects without getting
hard”), “and in these alone, we find copious nectar ready stored for
rapid suction in open nectaries. On the other hand, whenever the viscid
matter gets hard by exposure for a short time to the air, it would
manifestly be advantageous to the plant if insects were delayed in
obtaining the nectar; and in all such species the nectar is lodged
within intercellular spaces, so that it can be obtained only by the
inner membrane being penetrated at several points, and this will require
time. If this double relation is accidental, it is a fortunate accident
for the plants; but I cannot believe it to be so, and it appears to me
one of the most wonderful cases of adaptation which has ever been
recorded.”
Some orchids secrete instead of nectar a clear liquid like water. This
fluid is collected in a petal inserted at the lower part of the flower
and shaped into a deep cup-shaped receptacle. It does not attract
insects, but by wetting their wings compels them to leave the flower by
a different exit which passes close to the reproductive organs (_i.e._,
the anther and the stigma). The soft linings of the cup are greedily
devoured by certain insects, particularly by bees. Dr. Cruger, who
observed this, has often seen bees fall into the cup whereupon their
wings became so wet as to prevent their flying away, and they have been
obliged to get out by the channel that carries off the waste from the
reservoir. As the saturated bees creep along the narrow passage after
their involuntary immersion, they come inevitably in contact with the
stigma and the masses of pollen. The latter adhere to the bodies of the
bees and can be conveyed to the sticky stigma of a neighbouring flower.
[Illustration:
FIG. 1.—_Catasetum saccatum_ (from “La Lindenia,” Gand, 1890).
]
In other orchids (_Catasetum_, Fig. 1), the male elements are discharged
by a spring-like arrangement on the body of insects. When certain parts
of the flowers are touched, the pollinia are thrown off like arrows,
which, in the place of the barbs, have viscid swellings. “The insect,
disturbed by so sharp a blow, or after having eaten its fill, flies
sooner or later away to a female plant and, whilst standing in the same
position as before, the pollen-bearing end of the arrow is inserted into
the stigmatic cavity, and a mass of pollen is left on its viscid
surface.”[33]
After giving detailed descriptions of the cross-fertilisation of flowers
by such peculiar means, Darwin makes the following remark: “Who would
have been bold enough to have surmised that the propagation of a species
depended on so complex, so apparently artificial, and yet so admirable
an arrangement?”[34]
One orchid (_Herminium monorchis_, Fig. 2), which bears very small
flowers, is remarkable for the way in which it is fertilised by insects.
Only very small insects are able to penetrate the flowers. The space
being very limited these minute insects can enter the flower only in a
particular way, and at one of the corners. This causes the pollinia to
become attached always to the same place, which is on the outer side of
one of the two front legs. When the insect, the carrier of the pollinia,
enters a second flower, it can scarcely fail to fertilise the stigma,
which is on the corresponding side. Darwin said that it would be
difficult to find a case in which there was so marvellously complete an
adaptation to a very peculiar mode of fertilisation as the little flower
of _Herminium_.
[Illustration:
FIG. 2.—_Herminium monorchis_
(after Sowerby, “English Botany,” ix. 1869)
]
In addition to orchids, there are other flowers the organisation of
which is adapted in a remarkable way to fertilisation by insects. But to
find perfect harmony in the nature of living beings it is not necessary
to confine our observations to flowers. The animal world furnishes us
with numerous examples. To avoid going into the details of these, I
shall content myself with a description of the most remarkable
instances.
Every one has seen, flying near the ground, small, slender, and pretty
wasps. From time to time these bury themselves in the earth or sand, and
re-appear in a few minutes. These are the fossorial wasps, the
interesting habits of which have been studied by Mr. J. H. Fabre, of
Avignon. They are not gregarious, but lead solitary lives and differ in
their habits from their congeners. Bees feed their larvæ with honey and
pollen which they take to them during the whole period of their
development. Wasps are carnivorous, predatory insects, and bring their
spoils to their brood of soft and feeble larvæ which are unable to
provide for themselves. Bees and most wasps look after the welfare of
their young ones in the fashion of human parents in nurseries.
Fossorial wasps act differently; they never see their young. They lay
their eggs in burrows, sunk in the soil and hermetically sealed. The
larvæ are hatched underground and are never seen by the mother.
Provision sufficient for their development, however, is made in advance.
Before depositing eggs, the females sink the burrows, and fill them with
the spoils of the chase, which consist sometimes of spiders and
sometimes of crickets or other insects. Each species of fossorial wasps
preys on a particular kind of insect or on its allies, for the purpose
of provisioning the burrows. These wasps are most fastidious in the
choice of their food, and behave like collectors whose interest is only
in a single or a few species of small animals. Léon Dufour, the
well-known entomologist, was much struck by the ability displayed by
certain wasps (_Cerceris_, Fig. 3) in seeking out and capturing the
pretty beetles of the genus _Buprestis_, which he had great difficulty
in finding himself. In making a study of these beetles he collected the
material from the burrows of _Cerceris_, and so avoided the laborious
task of obtaining them in the natural state of freedom. The burrows were
filled with motionless, but perfectly well preserved, _Buprestes_.
Although dead Coleoptera dried up in a short time, those recovered from
the burrows remained in a good state of preservation for weeks. Léon
Dufour came to the conclusion that the _Cerceris_ kill their prey, but
inject into them some antiseptic liquid which perfectly preserves their
flesh and intestines.
[Illustration:
FIG. 3.—_Cerceris_ (after Buffon).
]
J. H. Fabre pursued the study of the habits of fossorial wasps further.
He ascertained that the captured insects were not dead, but only
paralysed. The continuance of the function of certain organs
demonstrated that the _Buprestes_, the weevils and other small creatures
collected in the burrows of fossorial wasps, were alive. They could even
perform some slight movements, but they were incapable of locomotion,
and so could not escape. The mechanism of this paralysis, as far as
could be ascertained by Fabre, is one of the most remarkable phenomena
in nature. The fossorial wasps, guided by their instinct, immediately
after having seized an insect or spider, bury their sting in the nervous
centre which controls the movements of the legs. When animals with soft
bodies, such as spiders and young crickets, are attacked, the operation
does not present any difficulties. But Coleoptera in general, and the
_Buprestes_ and weevils in particular, are furnished with a very hard
covering which cannot be perforated by the small and slender sting of a
fossorial wasp. To gain their object the wasps probe exactly between the
first and second pair of legs in the median line of the under surface of
the thorax. The skin is thinner at this spot, and they introduce their
sting into the ganglia from which arise the nerves of the legs. In the
case with the _Buprestes_ these ganglia are set close to one another,
and a single prick suffices to affect the nervous centres of three pairs
of legs. Once the sting has been inserted in this way the _Buprestis_
becomes paralysed, but lives for many days. “The _Cerceris_ which preys
on Coleoptera,” writes Fabre,[35] “appears to have made its choice
according to the dictates of an exact physiology and anatomy. It is
impossible to see in its proceedings the results of happy chance; more
than chance is required to explain adaptations so precise.”
After having filled the burrow with a sufficient quantity of insects or
spiders, fossorial wasps lay their eggs and carefully close up the
entrance. In due course the larva is hatched, and devours the food that
it finds close at hand. If the gathered insects were not paralysed, they
could easily escape from their prison; if they were dead, putrefaction
or desiccation (according to circumstances) would render them unfit for
the larvæ. It is therefore sheer necessity that is the factor in the
development of this marvellous instinct that induces the fossorial wasps
to attack the nervous centres of their prey. When one insect has been
devoured, the larva proceeds to another, and so on, until it is fully
grown, whereupon it envelops itself in a case that protects it during
the winter and following spring. In summer it changes at first into a
chrysalis, and later into a perfect insect. It frees itself from the
cocoon, takes to flight, and enters upon life like that of its mother,
which it has never seen.
Of the harmonious phenomena in nature it is indeed difficult to find
other examples so perfect as those of the habits of these fossorial
wasps, or of the mechanism for the fertilisation of orchids. These
harmonies in nature are constantly met with in the world of living
beings, and it is not astonishing that they have for a long time
attracted the attention of many observers and philosophers. As it seemed
impossible to attribute them to the organisms themselves, because of the
low rank and lack of intelligence of these, it has seemed only natural
to set them down as a manifestation of a superior force which organises
and directs all natural phenomena. This argument, however, omits one
side of the medal.
Any close investigation of organisation and life reveals that, beside
many most perfect harmonies, there are facts which prove the existence
of incomplete harmony or even absolute disharmony. The examination of
the flowers of orchids would lead one to the belief that each part, even
the smallest and apparently most insignificant, has its _rôle_ in the
mechanism for fertilisation and cross-fertilisation. In reality it is
not so. There are in certain orchids organs which do not fulfil any
function.
Even among the species of _Catasetum_, in which the pollinia are thrown
with force on the bodies of insects, there are some female flowers in
which the male organs are rudimentary and without utility. In these
flowers, according to Darwin,[36] “the two membranous sacks containing
the rudimentary pollen-masses never open, but they easily separate from
each other and from the anther. The tissue of which they are formed is
thick and pulpy. Like most rudimentary parts, the pollen-masses vary
much in size and form; they are only about one-tenth of the bulk of
those of the male.” There are then, without doubt, some structures that
are of no service.
The existence of these rudimentary pollinia, incapable of being
transported or of fertilising the female element, is easily explained by
the supposition that formerly the flowers of the _Catasetum_ were true
hermaphrodites, but that in the course of time the male organs have
become incompletely atrophied in certain flowers, in which, on the other
hand, the female part has increased. The occurrence of an actual
degeneration is shown by the existence of rudiments of the pollinia too
insignificant to accomplish their normal functions.
Rudimentary and useless organs are widely distributed, and we find them
in many places. Familiar instances are the atrophied eyes of animals
that live in the dark, and the sometimes rudimentary sexual organs of
many plants and animals.
Not only are orchids and other flowers adapted to fertilisation by means
of insects, but many insects display special adaptations to their habit
of visiting flowers. Butterflies, bees, and many other insects, possess
mouth organs modified for the purpose of penetrating flowers to secure
nectar or pollen. Other insects, again, are not so fortunate in this
respect. Darwin[37] on one occasion “found an extremely minute
Hymenopterous insect vainly struggling to escape, with its head cemented
by the hardened viscid matter to the crest of the rostellum and to the
tips of the pollinia (of an orchid, _Listera ovata_, Fig. 4). The insect
was not so large as one of the pollinia, and after causing the explosion
had not strength enough to remove them; it was punished for attempting a
work beyond its strength, and perished miserably.”
[Illustration:
FIG. 4.—_Listera ovata_ (after Barla, “Flora of Nice,” 1868).
]
Many insects, well adapted for the purpose, delight themselves by
sucking the nectar of flowers. Many others would wish to do the same,
but their want of adaptation baffles them. A small “lady-bird” loves the
sweet juice of flowers; it tries often to suck the nectar of the
dandelion, but without success. Hermann Müller[38] has described the
behaviour of this insect in procuring the nectar of _Erodium
cicutorium_. “The awkward way in which this beetle, unadapted to feed on
the plants, endeavours to obtain the honey, is too ludicrous not to be
mentioned. After taking up a position on the petal, it puts its mouth in
the direction of one of the honeycups which are situated on both sides
of the base of the petal. The petal soon breaks off, upon which the
insect fixes itself on a neighbouring sepal or falls to the ground with
the petal. In the first case it proceeds to creep over the flower and
ends by detaching all the petals; in the other case, on recovering from
the shock, it quickly ascends another stem of the same plant and begins
again. I have seen the same lady-bird fall four times in succession with
petals which it had detached without gaining wisdom.”
The instincts of insects, well developed for certain functions, often
present aberrations more or less whimsical and remarkable. The
caterpillars of some butterflies, before changing into chrysalids,
envelop themselves in a wellwoven cocoon capable of protecting them from
noxious influences. Protected by this covering, the caterpillar changes
into a chrysalid, and later into a butterfly, which perforates the end
of the cocoon in order to emerge. When any external agency destroys the
cocoon, normal metamorphosis becomes impossible, and the larva dies
before its maturity. Fabre[39] questioned whether the caterpillar during
the time of the weaving of the cocoon was capable of repairing it if it
was damaged. For this object he cut with a pair of scissors the end of a
cocoon in the course of construction by the caterpillar of the beautiful
peacock-butterfly. In spite of the hole thus produced, the caterpillar
continued its ordinary work without suspicion that it would be of no
avail. On this occasion “the caterpillar of the peacock-butterfly,
notwithstanding the certain fate of the future butterfly, continued
peaceably to spin, without in the least modifying the regular progress
of its labour; when the time had arrived for the putting in of the last
defensive stitches it placed them in the perilous breach, but neglected
to mend the destroyed part of the barricade. It performed its vain task,
ignoring what was indispensable for success.”
Even amongst fossorial wasps, the instincts of which are so admirably
developed, harmony is far from perfect. Fabre endeavoured to ascertain
what effect was produced on these insects by taking away the egg laid in
the burrow. He chose for this experiment the fossorial wasp _Pelopæus_
(Fig. 5), which preys on spiders. He took away the egg which had been
deposited in a carefully-prepared burrow, and watched the subsequent
manœuvres. “The _Pelopæus_ continued to store up spiders for the stolen
egg; it gathered provisions that were not to be eaten; it redoubled its
efforts to replenish a larder that I was constantly robbing with my
forceps.” The insect neither discontinued its fruitless task nor
appeared to be aware of its fruitlessness. Here, then, is an example of
a foiled maternal instinct that gained no useful end.
[Illustration:
FIG. 5.—_Pelopæus_ (after Buffon).
]
In connection with such a slaughter for the benefit of a progeny that
will never exist, I may mention observations relating to a quite
different order of phenomena. There are many creatures that kill and
devour their progeny. Not infrequently rabbits kill and devour all their
progeny, or leave them to die without food or care. Sometimes the
culprits are young rabbits without experience; but this aberration of
instinct is also met with in old rabbits, which once and for all have
contracted the habit of abandoning or eating their young. Some females
of other species of mammals and of birds have often been surprised in
the act of deserting or of killing their offspring.
Perversion of sexual instinct is frequent enough amongst animals.
Huber[40] states that when male ants have a lack of females they ravish
the workers, the attacks being fatal, as the sexual organs are
incompletely developed and functionally incapable. Abnormal pairing has
also been observed in the stag-beetle of the genus _Lucanus_, in bees,
and, above all, in cockchafers.[41] Higher animals, such as dogs,
furnish analogous examples of sexual perversion.
Onanism is well known amongst mammals. It is frequent among monkeys in
menageries, and also in rutting stags, the latter discharging the
seminal fluid by friction with trees. Stallions and mares have often
been observed in the act of satisfying their sexual appetites by
abnormal means. There are several other species (dogs, bears, chamois,
elephants, parrakeets, etc.,) which resort to onanism.[42]
These disharmonious instincts do not in the least cause the death of the
animals that manifest them. But there exist in nature instinctive
aberrations much more dangerous. Who has not seen in the summer numerous
insects gathered round lamps and candles, attracted by the light? Among
these are Coleoptera, Neuroptera (_Phryganea_), Ephemera, and, most
frequently of all, small nocturnal Lepidoptera. After flying round and
round the light several times, they singe their wings and die in
numbers. This instinct is so constant and so developed amongst many of
these insects, that it has been used against them for their own
destruction. Thus amongst the means advocated for destroying a moth,
_Botys sticticalis_, the caterpillars of which devour cereals and
beetroot,[43] is the lighting of numerous fires in the fields. The
moths, attracted by the light, fall in the flames and die in quantities.
When the usual swarms of may-flies emerge from the water, fishers make
straw fires on their boats, and the insects singe their wings. The
innumerable bodies incapable of flight fall into the water, and provide
a coveted food for the fish.[44] This disharmonious and fatal instinct
is displayed chiefly by nocturnal insects that rest during the day and
do not leave their retreats till after sunset. In the cornfields
Coleoptera of the genera _Anisoplia_ and _Rhizotrogus_, resembling each
other in form and general appearance, are to be found. When a fire is
lighted in the darkness of the night it is only the _Rhizotrogus_ that
approaches it at the risk of its life. The _Anisoplia_ remains quiet in
the midst of the corn. The latter kind of beetle pairs during the day,
while the _Rhizotrogi_ satisfy their sexual desires during the night.
Moreover, it is the males only of this species that fly about in the
darkness and approach the fire, whilst the females rest at home in the
plants.[45] It is probable, therefore, that light induces a sort of
sexual excitement in these male beetles. The males, searching for the
female, believe her to be in the midst of the flames, towards which they
fly without being conscious of the danger they incur.
Such an interpretation of this disharmonious and suicidal instinct is
confirmed by the fact that the moths attracted by fire are also almost
exclusively males. Moreover, entomologists have advised against the
lighting of fires by agriculturists in the belief that they destroy the
noxious _Botys_, as they maintain that the females are not attracted.
These latter therefore live on, and, being capable of laying eggs,
produce a generation of voracious caterpillars.
Of the _Ephemera_ attracted by fire in such great quantities males are
by far the more numerous. It is therefore really very probable that the
mad excitement which leads to the destruction of so many male insects,
represents a sort of sexual aberration. In this connection it is to be
remembered that, amongst Coleoptera, species exist of which the females,
hidden in the grass, produce intense light which attracts the males. In
the common glow-worm, the female, which is devoid of wings, alone shines
with the familiar greenish glitter. Even in species of which the two
sexes are luminous, the female shines more vividly. It is true that
there are some beetles with luminous larvæ, a fact that led Darwin[46]
to remark that the production of light by insects may serve to frighten
enemies. This is possible, and it is also possible that certain insects
make use of their luminosity to light their way in the darkness.[47]
But, notwithstanding this, the sexual character of the luminous organ is
so manifest in certain species that it is impossible to doubt its
function as a means of attracting the male.
In conclusion I may say that it is not my purpose at present to discuss
the meaning of an instinct so fatal to insect life. I wish only to point
out the frequency of the natural occurrence of disharmony, so that the
satisfaction of an instinct is fatal to so many of its possessors.
It is plain that an instinct, or any other form of disharmony leading to
destruction, cannot increase, or even endure very long. The perversion
of the maternal instinct tending to abandonment of the young is
destructive to the stock. In consequence, individuals affected by it do
not have the opportunity of transmitting the perversion. If all rabbits,
or a majority of them, left their young to die through neglect, it is
evident that the species would soon die out. On the contrary, mothers,
guided by their instinct to nourish and foster their offspring, will
produce a vigorous generation capable of transmitting the healthy
maternal instinct so essential for the preservation of the species. For
such a reason harmonious characters are more abundant in nature than
injurious peculiarities. The latter, because they are injurious to the
individual and to the species, cannot perpetuate themselves
indefinitely.
In this way there comes about a constant selection of characters. The
useful qualities are handed down and preserved, while noxious characters
perish and so disappear. Although disharmonies tend to the destruction
of a species, they may themselves disappear without having destroyed the
race in which they occur.
This continuous process of natural selection, which offers so good an
explanation of the transmutation and origin of species by means of
preservation of useful and destruction of harmful characters, was
discovered by Darwin and Wallace, and was established by the splendid
researches of the former of these.
Long before the appearance of man on the face of the earth, there were
some happy beings well adapted to their environment, and some unhappy
creatures that followed disharmonious instincts so as to imperil or to
destroy their lives. Were such creatures capable of reflection and
communication, plainly the fortunate among them, such as orchids and
fossorial wasps, would be on the side of the optimists; they would
declare this the best of all possible worlds, and insist that, to secure
happiness it is necessary only to follow natural instincts. On the other
hand, the disharmonious creatures, those ill adapted to the conditions
of life, would be pessimistic philosophers. Consider the case of the
lady-bird, driven by hunger and with a preference for honey, which
searches for it on flowers and meets only with failure, or of insects
driven by their instincts into the flames, only to lose their wings and
their lives; such creatures, plainly, would express as their idea of the
world that it was fashioned abominably, and that existence was a
mistake.
As for man, the creature most interesting to us, in what category does
he fall? Is he a being whose nature is in harmony with the conditions in
which he has to live, or is he out of harmony with his environment? A
critical examination is needed to answer these questions, and to such an
examination the pages to follow are devoted.