- Instincts comparable
with habits, but different
in their origin
- Instincts
graduated
- Aphides
and ants
- Instincts
variable
- Domestic
instincts, their origin
- Natural
instincts of the
cuckoo, ostrich, and parasitic
bees
- Slave-making
ants
- Hive-bee,
its cell-making
instinct
- Difficulties
on the theory
of the Natural
Selection
of
instincts
- Neuter
or sterile
insects
- Summary
THE subject of instinct might
have been worked into the previous
chapters; but I have thought
that it would be more convenient
to treat the subject separately,
especially as so wonderful an
instinct as that of the hive-bee
making its cells will probably
have occurred to many readers,
as a difficulty sufficient to
overthrow my whole theory. I
must premise, that I have nothing
to do with the origin of the
primary mental powers, any more
than I have with that of life
itself. We are concerned only
with the diversities of instinct
and of the other mental qualities
of animals within the same class.
I will not attempt any definition
of instinct. It would be easy
to show that several distinct
mental actions are commonly embraced
by this term; but every one understands
what is meant, when it is said
that instinct impels the cuckoo
to migrate and to lay her eggs
in other birds' nests. An action,
which we ourselves should require
experience to enable us to perform,
when performed by an animal,
more especially by a very young
one, without any experience,
and when performed by many individuals
in the same way, without their
knowing for what purpose it is
performed, is usually said to
be instinctive. But I could show
that none of these characters
of instinct are universal. A
little dose, as Pierre Huber
expresses it, of judgment or
reason, often comes into play,
even in animals very low in the
scale of nature.
Frederick Cuvier and several
of the older metaphysicians have
compared instinct with habit.
This comparison gives, I think,
a remarkably accurate notion
of the frame of mind under which
an instinctive action is performed,
but not of its origin. How unconsciously
many habitual actions are performed,
indeed not rarely in direct opposition
to our conscious will! yet they
may be modified by the will or
reason. Habits easily become
associated with other habits,
and with certain periods of time
and states of the body. When
once acquired, they often remain
constant throughout life. Several
other points of resemblance between
instincts and habits could be
pointed out. As in repeating
a well-known song, so in instincts,
one action follows another by
a sort of rhythm; if a person
be interrupted in a song, or
in repeating anything by rote,
he is generally forced to go
back to recover the habitual
train of thought: so P. Huber
found it was with a caterpillar,
which makes a very complicated
hammock; for if he took a caterpillar
which had completed its hammock
up to, say, the sixth stage of
construction, and put it into
a hammock completed up only to
the third stage, the caterpillar
simply re-performed the fourth,
fifth, and sixth stages of construction.
If, however, a caterpillar were
taken out of a hammock made up,
for instance, to the third stage,
and were put into one finished
up to the sixth stage, so that
much of its work was already
done for it, far from feeling
the benefit of this, it was much
embarrassed, and, in order to
complete its hammock, seemed
forced to start from the third
stage, where it had left off,
and thus tried to complete the
already finished work.
If we suppose any habitual
action to become inherited and
I think it can be shown that
this does sometimes happen then
the resemblance between what
originally was a habit and an
instinct becomes so close as
not to be distinguished. If Mozart,
instead of playing the pianoforte
at three years old with wonderfully
little practice, had played a
tune with no practice at all,
be might truly be said to have
done so instinctively. But it
would be the most serious error
to suppose that the greater number
of instincts have been acquired
by habit in one generation, and
then transmitted by inheritance
to succeeding generations. It
can be clearly shown that the
most wonderful instincts with
which we are acquainted, namely,
those of the hive-bee and of
many ants, could not possibly
have been thus acquired.
It will be universally admitted
that instincts are as important
as corporeal structure for the
welfare of each species, under
its present conditions of life.
Under changed conditions of life,
it is at least possible that
slight modifications of instinct
might be profitable to a species;
and if it can be shown that instincts
do vary ever so little, then
I can see no difficulty in natural
selection preserving and continually
accumulating variations of instinct
to any extent that may be profitable.
It is thus, as I believe, that
all the most complex and wonderful
instincts have originated. As
modifications of corporeal structure
arise from, and are increased
by, use or habit, and are diminished
or lost by disuse, so I do not
doubt it has been with instincts.
But I believe that the effects
of habit are of quite subordinate
importance to the effects of
the natural selection of what
may be called accidental variations
of instincts; that is of variations
produced by the same unknown
causes which produce slight deviations
of bodily structure.
No complex
instinct can possibly be produced
through natural selection,
except by the slow and gradual
accumulation of numerous, slight,
yet profitable, variations. Hence,
as in the case of corporeal structures,
we ought to find in nature, not
the actual transitional gradations
by which each complex instinct
has been acquired for these could
be found only in the lineal ancestors
of each species but we ought
to find in the collateral lines
of descent some evidence of such
gradations; or we ought at least
to be able to show that gradations
of some kind are possible; and
this we certainly can do. I have
been surprised to find, making
allowance for the instincts of
animals having been but little
observed except in Europe and
North America, and for no instinct
being known amongst extinct species,
how very generally gradations,
leading to the most complex instincts,
can be discovered. The canon
of 'Natura non facit saltum'
applies with almost equal force
to instincts as to bodily organs.
Changes of instinct may sometimes
be facilitated by the same species
having different instincts at
different periods of life, or
at different seasons of the year,
or when placed under different
circumstances, &c.; in which
case either one or the other
instinct might be preserved by
natural selection. And such instances
of diversity of instinct in the
same species can be shown to
occur in nature.
Again as in the case of corporeal
structure, and conformably with
my theory, the instinct of each
species is good for itself, but
has never, as far as we can judge,
been produced for the exclusive
good of others. One of the strongest
instances of an animal apparently
performing an action for the
sole good of another, with which
I am acquainted, is that of aphides
voluntarily yielding their sweet
excretion to ants: that they
do so voluntarily, the following
facts show. I removed all the
ants from a group of about a
dozen aphides on a dock-plant,
and prevented their attendance
during several hours. After this
interval, I felt sure that the
aphides would want to excrete.
I watched them for some time
through a lens, but not one excreted;
I then tickled and stroked them
with a hair in the same manner,
as well as I could, as the ants
do with their antennae; but not
one excreted. Afterwards I allowed
an ant to visit them, and it
immediately seemed, by its eager
way of running about, to be well
aware what a rich flock it had
discovered; it then began to
play with its antennae on the
abdomen first of one aphis and
then of another; and each aphis,
as soon as it felt the antennae,
immediately lifted up its abdomen
and excreted a limpid drop of
sweet juice, which was eagerly
devoured by the ant. Even the
quite young aphides behaved in
this manner, showing that the
action was instinctive, and not
the result of experience. But
as the excretion is extremely
viscid, it is probably a convenience
to the aphides to have it removed;
and therefore probably the aphides
do not instinctively excrete
for the sole good of the ants.
Although I do not believe that
any animal in the world performs
an action for the exclusive good
of another of a distinct species,
yet each species tries to take
advantage of the instincts of
others, as each takes advantage
of the weaker bodily structure
of others. So again, in some
few cases, certain instincts
cannot be considered as absolutely
perfect; but as details on this
and other such points are not
indispensable, they may be here
passed over.
As some degree of variation
in instincts under a state of
nature, and the inheritance of
such variations, are indispensable
for the action of natural selection,
as many instances as possible
ought to have been here given;
but want of space prevents me.
I can only assert, that instincts
certainly do vary for instance,
the migratory instinct, both
in extent and direction, and
in its total loss. So it is with
the nests of birds, which vary
partly in dependence on the situations
chosen, and on the nature and
temperature of the country inhabited,
but often from causes wholly
unknown to us: Audubon has given
several remarkable cases of differences
in nests of the same species
in the northern and southern
United States. Fear of any particular
enemy is certainly an instinctive
quality, as may be seen in nestling
birds, though it is strengthened
by experience, and by the sight
of fear of the same enemy in
other animals. But fear of man
is slowly acquired, as I have
elsewhere shown, by various animals
inhabiting desert islands; and
we may see an instance of this,
even in England, in the greater
wildness of all our large birds
than of our small birds; for
the large birds have been most
persecuted by man. We may safely
attribute the greater wildness
of our large birds to this cause;
for in uninhabited islands large
birds are not more fearful than
small; and the magpie, so wary
in England, is tame in Norway,
as is the hooded crow in Egypt.
That the general disposition
of individuals of the same species,
born in a state of nature, is
extremely diversified, can be
shown by a multitude of facts.
Several cases also, could be
given, of occasional and strange
habits in certain species, which
might, if advantageous to the
species, give rise, through natural
selection, to quite new instincts.
But I am well aware that these
general statements, without facts
given in detail, can produce
but a feeble effect on the reader's
mind. I can only repeat my assurance,
that I do not speak without good
evidence.
The possibility, or even probability,
of inherited variations of instinct
in a state of nature will be
strengthened by briefly considering
a few cases under domestication.
We shall thus also be enabled
to see the respective parts which
habit and the selection of so-called
accidental variations have played
in modifying the mental qualities
of our domestic animals. A number
of curious and authentic instances
could be given of the inheritance
of all shades of disposition
and tastes, and likewise of the
oddest tricks, associated with
certain frames of mind or periods
of time. But let us look to the
familiar case of the several
breeds of dogs: it cannot be
doubted that young pointers (I
have myself seen a striking instance)
will sometimes point and even
back other dogs the very first
time that they are taken out;
retrieving is certainly in some
degree inherited by retrievers;
and a tendency to run round,
instead of at, a flock of sheep,
by shepherd-dogs. I cannot see
that these actions, performed
without experience by the young,
and in nearly the same manner
by each individual, performed
with eager delight by each breed,
and without the end being known,
for the young pointer can no
more know that he points to aid
his master, than the white butterfly
knows why she lays her eggs on
the leaf of the cabbage, I cannot
see that these actions differ
essentially from true instincts.
If we were to see one kind of
wolf, when young and without
any training, as soon as it scented
its prey, stand motionless like
a statue, and then slowly crawl
forward with a peculiar gait;
and another kind of wolf rushing
round, instead of at, a herd
of deer, and driving them to
a distant point, we should assuredly
call these actions instinctive.
Domestic instincts, as they may
be called, are certify far less
fixed or invariable than natural
instincts; but they have been
acted on by far less rigorous
selection, and have been transmitted
for an incomparably shorter period,
under less fixed conditions of
life.
How strongly these domestic
instincts, habits, and dispositions
are inherited, and how curiously
they become mingled, is well
shown when different breeds of
dogs are crossed. Thus it is
known that a cross with a bull-dog
has affected for many generations
the courage and obstinacy of
greyhounds; and a cross with
a greyhound has given to a whole
family of shepherd-dogs a tendency
to hunt hares. These domestic
instincts, when thus tested by
crossing, resemble natural instincts,
which in a like manner become
curiously blended together, and
for a long period exhibit traces
of the instincts of either parent:
for example, Le Roy describes
a dog, whose great-grandfather
was a wolf, and this dog showed
a trace of its wild parentage
only in one way, by not coming
in a straight line to his master
when called.
Domestic instincts are sometimes
spoken of as actions which have
become inherited solely from
long-continued and compulsory
habit, but this, I think, is
not true. No one would ever have
thought of teaching, or probably
could have taught, the tumbler-pigeon
to tumble, an action which, as
I have witnessed, is performed
by young birds, that have never
seen a pigeon tumble. We may
believe that some one pigeon
showed a slight tendency to this
strange habit, and that the long-continued
selection of the best individuals
in successive generations made
tumblers what they now are; and
near Glasgow there are house-tumblers,
as I hear from Mr Brent, which
cannot fly eighteen inches high
without going head over heels.
It may be doubted whether any
one would have thought of training
a dog to point, had not some
one dog naturally shown a tendency
in this line; and this is known
occasionally to happen, as I
once saw in a pure terrier. When
the first tendency was once displayed,
methodical selection and the
inherited effects of compulsory
training in each successive generation
would soon complete the work;
and unconscious selection is
still at work, as each man tries
to procure, without intending
to improve the breed, dogs which
will stand and hunt best. On
the other hand, habit alone in
some cases has sufficed; no animal
is more difficult to tame than
the young of the wild rabbit;
scarcely any animal is tamer
than the young of the tame rabbit;
but I do not suppose that domestic
rabbits have ever been selected
for tameness; and I presume that
we must attribute the whole of
the inherited change from extreme
wildness to extreme tameness,
simply to habit and long-continued
close confinement.
Natural instincts are lost
under domestication: a remarkable
instance of this is seen in those
breeds of fowls which very rarely
or never become 'broody,' that
is, never wish to sit on their
eggs. Familiarity alone prevents
our seeing how universally and
largely the minds of our domestic
animals have been modified by
domestication. It is scarcely
possible to doubt that the love
of man has become instinctive
in the dog. All wolves, foxes,
jackals, and species of the cat
genus, when kept tame, are most
eager to attack poultry, sheep,
and pigs; and this tendency has
been found incurable in dogs
which have been brought home
as puppies from countries, such
as Tierra del Fuego and Australia,
where the savages do not keep
these domestic animals. How rarely,
on the other hand, do our civilised
dogs, even when quite young,
require to be taught not to attack
poultry, sheep, and pigs! No
doubt they occasionally do make
an attack, and are then beaten;
and if not cured, they are destroyed;
so that habit, with some degree
of selection, has probably concurred
in civilising by inheritance
our dogs. On the other hand,
young chickens have lost, wholly
by habit, that fear of the dog
and cat which no doubt was originally
instinctive in them, in the same
way as it is so plainly instinctive
in young pheasants, though reared
under a hen. It is not that chickens
have lost all fear, but fear
only of dogs and cats, for if
the hen gives the danger-chuckle,
they will run (more especially
young turkeys) from under her,
and conceal themselves in the
surrounding grass or thickets;
and this is evidently done for
the instinctive purpose of allowing,
as we see in wild ground-birds,
their mother to fly away. But
this instinct retained by our
chickens has become useless under
domestication, for the mother-hen
has almost lost by disuse the
power of flight.
Hence, we may conclude, that
domestic instincts have been
acquired and natural instincts
have been lost partly by habit,
and partly by man selecting and
accumulating during successive
generations, peculiar mental
habits and actions, which at
first appeared from what we must
in our ignorance call an accident.
In some cases compulsory habit
alone has sufficed to produce
such inherited mental changes;
in other cases compulsory habit
has done nothing, and all has
been the result of selection,
pursued both methodically and
unconsciously; but in most cases,
probably, habit and selection
have acted together.
We shall, perhaps, best understand
how instincts in a state of nature
have become modified by selection,
by considering a few cases. I
will select only three, out of
the several which I shall have
to discuss in my future work,
namely, the instinct which leads
the cuckoo to lay her eggs in
other birds' nests; the slave-making
instinct of certain ants; and
the comb-making power of the
hive-bee: these two latter instincts
have generally, and most justly,
been ranked by naturalists as
the most wonderful of all known
instincts.
It is now commonly admitted
that the more immediate and final
cause of the cuckoo's instinct
is, that she lays her eggs, not
daily, but at intervals of two
or three days; so that, if she
were to make her own nest and
sit on her own eggs, those first
laid would have to be left for
some time unincubated, or there
would be eggs and young birds
of different ages in the same
nest. If this were the case,
the process of laying and hatching
might be inconveniently long,
more especially as she has to
migrate at a very early period;
and the first hatched young would
probably have to be fed by the
male alone. But the American
cuckoo is in this predicament;
for she makes her own nest and
has eggs and young successively
hatched, all at the same time.
It has been asserted that the
American cuckoo occasionally
lays her eggs in other birds'
nests; but I hear on the high
authority of Dr. Brewer, that
this is a mistake. Nevertheless,
I could give several instances
of various birds which have been
known occasionally to lay their
eggs in other birds' nests. Now
let us suppose that the ancient
progenitor of our European cuckoo
had the habits of the American
cuckoo; but that occasionally
she laid an egg in another bird's
nest. If the old bird profited
by this occasional habit, or
if the young were made more vigorous
by advantage having been taken
of the mistaken maternal instinct
of another bird, than by their
own mother's care, encumbered
as she can hardly fail to be
by having eggs and young of different
ages at the same time; then the
old birds or the fostered young
would gain an advantage. And
analogy would lead me to believe,
that the young thus reared would
be apt to follow by inheritance
the occasional and aberrant habit
of their mother, and in their
turn would be apt to lay their
eggs in other birds' nests, and
thus be successful in rearing
their young. By a continued process
of this nature, I believe that
the strange instinct of our cuckoo
could be, and has been, generated.
I may add that, according to
Dr. Gray and to some other observers,
the European cuckoo has not utterly
lost all maternal love and care
for her own offspring.
The occasional habit of birds
laying their eggs in other birds'
nests, either of the same or
of a distinct species, is not
very uncommon with the Gallinaceae;
and this perhaps explains the
origin of a singular instinct
in the allied group of ostriches.
For several hen ostriches, at
least in the case of the American
species, unite and lay first
a few eggs in one nest and then
in another; and these are hatched
by the males. This instinct may
probably be accounted for by
the fact of the hens laying a
large number of eggs; but, as
in the case of the cuckoo, at
intervals of two or three days.
This instinct, however, of the
American ostrich has not as yet
been perfected; for a surprising
number of eggs lie strewed over
the plains, so that in one day's
hunting I picked up no less than
twenty lost and wasted eggs.
Many bees are parasitic, and
always lay their eggs in the
nests of bees of other kinds.
This case is more remarkable
than that of the cuckoo; for
these bees have not only their
instincts but their structure
modified in accordance with their
parasitic habits; for they do
not possess the pollen-collecting
apparatus which would be necessary
if they had to store food for
their own young. Some species,
likewise, of Sphegidae (wasp-like
insects) are parasitic on other
species; and M. Fabre has lately
shown good reason for believing
that although the Tachytes nigra
generally makes its own burrow
and stores it with paralysed
prey for its own larvae to feed
on, yet that when this insect
finds a burrow already made and
stored by another sphex, it takes
advantage of the prize, and becomes
for the occasion parasitic. In
this case, as with the supposed
case of the cuckoo, I can see
no difficulty in natural selection
making an occasional habit permanent,
if of advantage to the species,
and if the insect whose nest
and stored food are thus feloniously
appropriated, be not thus exterminated.
Slave-making instinct. This
remarkable instinct was first
discovered in the Formica (Polyerges)
rufescens by Pierre Huber, a
better observer even than his
celebrated father. This ant is
absolutely dependent on its slaves;
without their aid, the species
would certainly become extinct
in a single year. The males and
fertile females do no work. The
workers or sterile females, though
most energetic and courageous
in capturing slaves, do no other
work. They are incapable of making
their own nests, or of feeding
their own larvae. When the old
nest is found inconvenient, and
they have to migrate, it is the
slaves which determine the migration,
and actually carry their masters
in their jaws. So utterly helpless
are the masters, that when Huber
shut up thirty of them without
a slave, but with plenty of the
food which they like best, and
with their larvae and pupae to
stimulate them to work, they
did nothing; they could not even
feed themselves, and many perished
of hunger. Huber then introduced
a single slave (F. fusca), and
she instantly set to work, fed
and saved the survivors; made
some cells and tended the larvae,
and put all to rights. What can
be more extraordinary than these
well-ascertained facts? If we
had not known of any other slave-making
ant, it would have been hopeless
to have speculated how so wonderful
an instinct could have been perfected.
Formica sanguinea was likewise
first discovered by P. Huber
to be a slave-making ant. This
species is found in the southern
parts of England, and its habits
have been attended to by Mr.
F. Smith, of the British Museum,
to whom I am much indebted for
information on this and other
subjects. Although fully trusting
to the statements of Huber and
Mr. Smith, I tried to approach
the subject in a sceptical frame
of mind, as any one may well
be excused for doubting the truth
of so extraordinary and odious
an instinct as that of making
slaves. Hence I will give the
observations which I have made
myself made, in some little detail.
I opened fourteen nests of F.
sanguinea, and found a few slaves
in all. Males and fertile females
of the slave-species are found
only in their own proper communities,
and have never been observed
in the nests of F. sanguinea.
The slaves are black and not
above half the size of their
red masters, so that the contrast
in their appearance is very great.
When the nest is slightly disturbed,
the slaves occasionally come
out, and like their masters are
much agitated and defend their
nest: when the nest is much disturbed
and the larvae and pupae are
exposed, the slaves work energetically
with their masters in carrying
them away to a place of safety.
Hence, it is clear, that the
slaves feel quite at home. During
the months of June and July,
on three successive years, I
have watched for many hours several
nests in Surrey and Sussex, and
never saw a slave either leave
or enter a nest. As, during these
months, the slaves are very few
in number, I thought that they
might behave differently when
more numerous; but Mr. Smith
informs me that he has watched
the nests at various hours during
May, June and August, both in
Surrey and Hampshire, and has
never seen the slaves, though
present in large numbers in August,
either leave or enter the nest.
Hence he considers them as strictly
household slaves. The masters,
on the other hand, may be constantly
seen bringing in materials for
the nest, and food of all kinds.
During the present year, however,
in the month of July, I came
across a community with an unusually
large stock of slaves, and I
observed a few slaves mingled
with their masters leaving the
nest, and marching along the
same road to a tall Scotch-fir-tree,
twenty-five yards distant, which
they ascended together, probably
in search of aphides or cocci.
According to Huber, who had ample
opportunities for observation,
in Switzerland the slaves habitually
work with their masters in making
the nest, and they alone open
and close the doors in the morning
and evening; and, as Huber expressly
states, their principal office
is to search for aphides. This
difference in the usual habits
of the masters and slaves in
the two countries, probably depends
merely on the slaves being captured
in greater numbers in Switzerland
than in England.
One day I fortunately chanced
to witness a migration from one
nest to another, and it was a
most interesting spectacle to
behold the masters carefully
carrying, as Huber has described,
their slaves in their jaws. Another
day my attention was struck by
about a score of the slave-makers
haunting the same spot, and evidently
not in search of food; they approached
and were vigorously repulsed
by an independent community of
the slave species (F. fusca);
sometimes as many as three of
these ants clinging to the legs
of the slave-making F. sanguinea.
The latter ruthlessly killed
their small opponents, and carried
their dead bodies as food to
their nest, twenty-nine yards
distant; but they were prevented
from getting any pupae to rear
as slaves. I then dug up a small
parcel of the pupae of F. fusca
from another nest, and put them
down on a bare spot near the
place of combat; they were eagerly
seized, and carried off by the
tyrants, who perhaps fancied
that, after all, they had been
victorious in their late combat.
At the same time I laid on
the same place a small parcel
of the pupae of another species,
F. flava, with a few of these
little yellow ants still clinging
to the fragments of the nest.
This species is sometimes, though
rarely, made into slaves, as
has been described by Mr Smith.
Although so small a species,
it is very courageous, and I
have seen it ferociously attack
other ants. In one instance I
found to my surprise an independent
community of F. flava under a
stone beneath a nest of the slave-making
F. sanguinea; and when I had
accidentally disturbed both nests,
the little ants attacked their
big neighbours with surprising
courage. Now I was curious to
ascertain whether F. sanguinea
could distinguish the pupae of
F. fusca, which they habitually
make into slaves, from those
of the little and furious F.
flava, which they rarely capture,
and it was evident that they
did at once distinguish them:
for we have seen that they eagerly
and instantly seized the pupae
of F. fusca, whereas they were
much terrified when they came
across the pupae, or even the
earth from the nest of F. flava,
and quickly ran away; but in
about a quarter of an hour, shortly
after all the little yellow ants
had crawled away, they took heart
and carried off the pupae.
One evening I visited another
community of F. sanguinea, and
found a number of these ants
entering their nest, carrying
the dead bodies of F. fusca (showing
that it was not a migration)
and numerous pupae. I traced
the returning file burthened
with booty, for about forty yards,
to a very thick clump of heath.
whence I saw the last individual
of F. sanguinea emerge, carrying
a pupa; but I was not able to
find the desolated nest in the
thick heath. The nest, however,
must have been close at hand,
for two or three individuals
of F. fusca were rushing about
in the greatest agitation, and
one was perched motionless with
its own pupa in its mouth on
the top of a spray of heath over
its ravaged home.
Such are the facts, though
they did not need confirmation
by me, in regard to the wonderful
instinct of making slaves. Let
it be observed what a contrast
the instinctive habits of F.
sanguinea present with those
of the F. rufescens. The latter
does not build its own nest,
does not determine its own migrations,
does not collect food for itself
or its young, and cannot even
feed itself: it is absolutely
dependent on its numerous slaves.
Formica sanguinea, on the other
hand, possesses much fewer slaves,
and in the early part of the
summer extremely few. The masters
determine when and where a new
nest shall be formed, and when
they migrate, the masters carry
the slaves. Both in Switzerland
and England the slaves seem to
have the exclusive care of the
larvae, and the masters alone
go on slave-making expeditions.
In Switzerland the slaves and
masters work together, making
and bringing materials for the
nest: both, but chiefly the slaves,
tend, and milk as it may be called,
their aphides; and thus both
collect food for the community.
In England the masters alone
usually leave the nest to collect
building materials and food for
themselves, their slaves and
larvae. So that the masters in
this country receive much less
service from their slaves than
they do in Switzerland.
By what steps the instinct
of F. sanguinea originated I
will not pretend to conjecture.
But as ants, which are not slave-makers,
will, as I have seen, carry off
pupae of other species, if scattered
near their nests, it is possible
that pupae originally stored
as food might become developed;
and the ants thus unintentionally
reared would then follow their
proper instincts, and do what
work they could. If their presence
proved useful to the species
which had seized them if it were
more advantageous to this species
to capture workers than to procreate
them the habit of collecting
pupae originally for food might
by natural selection be strengthened
and rendered permanent for the
very different purpose of raising
slaves. When the instinct was
once acquired, if carried out
to a much less extent even than
in our British F. sanguinea,
which, as we have seen, is less
aided by its slaves than the
same species in Switzerland,
I can see no difficulty in natural
selection increasing and modifying
the instinct always supposing
each modification to be of use
to the species until an ant was
formed as abjectly dependent
on its slaves as is the Formica
rufescens.
Cell-making instinct of
the Hive-Bee. I will not
here enter on minute details
on this subject, but will merely
give an outline of the conclusions
at which I have arrived. He
must be a dull man who can
examine the exquisite structure
of a comb, so beautifully adapted
to its end, without enthusiastic
admiration. We hear from mathematicians
that bees have practically
solved a recondite problem,
and have made their cells of
the proper shape to hold the
greatest possible amount of
honey, with the least possible
consumption of previous wax
in their construction. It has
been remarked that a skilful
workman, with fitting tools
and measures, would find it
very difficult to make cells
of wax of the true form, though
this is perfectly effected
by a crowd of bees working
in a dark hive. Grant whatever
instincts you please, and it
seems at first quite inconceivable
how they can make all the necessary
angles and planes, or even
perceive when they are correctly
made. But the difficulty is
not nearly so great as it at
first appears: all this beautiful
work can be shown, I think,
to follow from a few very simple
instincts.
I was led to investigate this
subject by Mr. Waterhouse, who
has shown that the form of the
cell stands in close relation
to the presence of adjoining
cells; and the following view
may, perhaps, be considered only
as a modification of this theory.
Let us look to the great principle
of gradation, and see whether
Nature does not reveal to us
her method of work. At one end
of a short series we have humble-bees,
which use their old cocoons to
hold honey, sometimes adding
to them short tubes of wax, and
likewise making separate and
very irregular rounded cells
of wax. At the other end of the
series we have the cells of the
hive-bee, placed in a double
layer: each cell, as is well
know, is an hexagonal prism,
with the basal edges of its six
sides bevelled so as to join
on to a pyramid, formed of three
rhombs. These rhombs have certain
angles, and the three which form
the pyramidal base of a single
cell on one side of the comb,
enter into the composition of
the bases of three adjoining
cells on the opposite side. In
the series between the extreme
perfection of the cells of the
hive-bee and the simplicity of
those of the humble-bee, we have
the cells of the Mexican Melipona
domestica, carefully described
and figured by Pierre Huber.
The Melipona itself is intermediate
in structure between the hive
and humble bee, but more nearly
related to the latter: it forms
a nearly regular waxen comb of
cylindrical cells, in which the
young are hatched, and, in addition,
some large cells of wax for holding
honey. These latter cells are
nearly spherical and of nearly
equal sizes, and are aggregated
into an irregular mass. But the
important point to notice, is
that these cells are always made
at that degree of nearness to
each other, that they would have
intersected or broken into each
other, if the spheres had been
completed; but this is never
permitted, the bees building
perfectly flat walls of wax between
the spheres which thus tend to
intersect. Hence each cell consists
of an outer spherical portion
and of two, three, or more perfectly
flat surfaces, according as the
cell adjoins two, three or more
other cells. When one cell comes
into contact with three other
cells, which, from the spheres
being nearly of the same size,
is very frequently and necessarily
the case, the three flat surfaces
are united into a pyramid; and
this pyramid, as Huber has remarked,
is manifestly a gross imitation
of the three-sided pyramidal
basis of the cell of the hive-bee.
As in the cells of the hive-bee,
so here, the three plane surfaces
in any one cell necessarily enter
into the construction of three
adjoining cells. It is obvious
that the Melipona saves wax by
this manner of building; for
the flat walls between the adjoining
cells are not double, but are
of the same thickness as the
outer spherical portions, and
yet each flat portion forms a
part of two cells.
Reflecting on this case, it
occurred to me that if the Melipona
had made its spheres at some
given distance from each other,
and had made them of equal sizes
and had arranged them symmetrically
in a double layer, the resulting
structure would probably have
been as perfect as the comb of
the hive-bee. Accordingly I wrote
to Professor Miller, of Cambridge,
and this geometer has kindly
read over the following statement,
drawn up from his information,
and tells me that it is strictly
correct:-
If a number of equal spheres
be described with their centres
placed in two parallel layers;
with the centre of each sphere
at the distance of radius X /sqrt[2]
or radius X 1.41421 (or at some
lesser distance), from the centres
of the six surrounding spheres
in the same layer; and at the
same distance from the centres
of the adjoining spheres in the
other and parallel layer; then,
if planes of intersection between
the several spheres in both layers
be formed, there will result
a double layer of hexagonal prisms
united together by pyramidal
bases formed of three rhombs;
and the rhombs and the sides
of the hexagonal prisms will
have every angle identically
the same with the best measurements
which have been made of the cells
of the hive-bee.
Hence we may safely conclude
that if we could slightly modify
the instincts already possessed
by the Melipona, and in themselves
not very wonderful, this bee
would make a structure as wonderfully
perfect as that of the hive-bee.
We must suppose the Melipona
to make her cells truly spherical,
and of equal sizes; and this
would not be very surprising,
seeing that she already does
so to a certain extent, and seeing
what perfectly cylindrical burrows
in wood many insects can make,
apparently by turning round on
a fixed point. We must suppose
the Melipona to arrange her cells
in level layers, as she already
does her cylindrical cells; and
we must further suppose, and
this is the greatest difficulty,
that she can somehow judge accurately
at what distance to stand from
her fellow-labourers when several
are making their spheres; but
she is already so far enabled
to judge of distance, that she
always describes her spheres
so as to intersect largely; and
then she unites the points of
intersection by perfectly flat
surfaces. We have further to
suppose, but this is no difficulty,
that after hexagonal prisms have
been formed by the intersection
of adjoining spheres in the same
layer, she can prolong the hexagon
to any length requisite to hold
the stock of honey; in the same
way as the rude humble-bee adds
cylinders of wax to the circular
mouths of her old cocoons. By
such modifications of instincts
in themselves not very wonderful,
hardly more wonderful than those
which guide a bird to make its
nest, I believe that the hive-bee
has acquired, through natural
selection, her inimitable architectural
powers.
But this theory can be tested
by experiment. Following the
example of Mr Tegetmeier, I separated
two combs, and put between them
a long, thick, square strip of
wax: the bees instantly began
to excavate minute circular pits
in it; and as they deepened these
little pits, they made them wider
and wider until they were converted
into shallow basins, appearing
to the eye perfectly true or
parts of a sphere, and of about
the diameter of a cell. It was
most interesting to me to observe
that wherever several bees had
begun to excavate these basins
near together, they had begun
their work at such a distance
from each other, that by the
time the basins had acquired
the above stated width (i.e. about
the width of an ordinary cell),
and were in depth about one sixth
of the diameter of the sphere
of which they formed a part,
the rims of the basins intersected
or broke into each other. As
soon as this occurred, the bees
ceased to excavate, and began
to build up flat walls of wax
on the lines of intersection
between the basins, so that each
hexagonal prism was built upon
the festooned edge of a smooth
basin, instead of on the straight
edges of a three-sided pyramid
as in the case of ordinary cells.
I then put into the hive, instead
of a thick, square piece of wax,
a thin and narrow, knife-edged
ridge, coloured with vermilion.
The bees instantly began on both
sides to excavate little basins
near to each other, in the same
way as before; but the ridge
of wax was so thin, that the
bottoms of the basins, if they
had been excavated to the same
depth as in the former experiment,
would have broken into each other
from the opposite sides. The
bees, however, did not suffer
this to happen, and they stopped
their excavations in due time;
so that the basins, as soon as
they had been a little deepened,
came to have flat bottoms; and
these flat bottoms, formed by
thin little plates of the vermilion
wax having been left ungnawed,
were situated, as far as the
eye could judge, exactly along
the planes of imaginary intersection
between the basins on the opposite
sides of the ridge of wax. In
parts, only little bits, in other
parts, large portions of a rhombic
plate had been left between the
opposed basins, but the work,
from the unnatural state of things,
had not been neatly performed.
The bees must have worked at
very nearly the same rate on
the opposite side of the ridge
of vermilion wax, as they circularly
gnawed away and deepened the
basins on both sides, in order
to have succeeded in thus leaving
flat plates between the basins,
by stopping work along the intermediate
planes or planes of intersection.
Considering how flexible thin
wax is, I do not see that there
is any difficulty in the bees,
whilst at work on the two sides
of a strip of wax, perceiving
when they have gnawed the wax
away to the proper thinness,
and then stopping their work.
In ordinary combs it has appeared
to me that the bees do not always
succeed in working at exactly
the same rate from the opposite
sides; for I have noticed half-completed
rhombs at the base of a just-commenced
cell, which were slightly concave
on one side, where I suppose
that the bees had excavated too
quickly, and convex on the opposed
side, where the bees had worked
less quickly. In one well-marked
instance, I put the comb back
into the hive and allowed the
bees to go on working for a short
time and again examined the cell,
and I found that the rhombic
plate had been completed, and
had become perfectly flat: it
was absolutely impossible, from
the extreme thinness of the little
rhombic plate, that they could
have affected this by gnawing
away the convex side; and I suspect
that the bees in such cases stand
in the opposed cells and push
and bend the ductile and warm
wax (which as I have tried is
easily done) into its proper
intermediate plane, and thus
flatten it.
From the experiment of the
ridge of vermilion wax, we can
clearly see that if the bees
were to build for themselves
a thin wall of wax, they could
make their cells of the proper
shape, by standing at the proper
distance from each other, by
excavating at the same rate,
and by endeavouring to make equal
spherical hollows, but never
allowing the spheres to break
into each other. Now bees, as
may be clearly seen by examining
the edge of a growing comb, do
make a rough, circumferential
wall or rim all round the comb;
and they gnaw into this from
the opposite sides, always working
circularly as they deepen each
cell. They do not make the whole
three-sided pyramidal base of
any one cell at the same time,
but only the one rhombic plate
which stands on the extreme growing
margin, or the two plates, as
the case may be; and they never
complete the upper edges of the
rhombic plates, until the hexagonal
walls are commenced. Some of
these statements differ from
those made by the justly celebrated
elder Huber, but I am convinced
of their accuracy; and if I had
space, I could show that they
are conformable with my theory.
Huber's statement that the
very first cell is excavated
out of a little parallel-sided
wall of wax, is not, as far as
I have seen, strictly correct;
the first commencement having
always been a little hood of
wax; but I will not here enter
on these details. We see how
important a part excavation plays
in the construction of the cells;
but it would be a great error
to suppose that the bees cannot
build up a rough wall of wax
in the proper position that is,
along the plane of intersection
between two adjoining spheres.
I have several specimens showing
clearly that they can do this.
Even in the rude circumferential
rim or wall of wax round a growing
comb, flexures may sometimes
be observed, corresponding in
position to the planes of the
rhombic basal plates of future
cells. But the rough wall of
wax has in every case to be finished
off, by being largely gnawed
away on both sides. The manner
in which the bees build is curious;
they always make the first rough
wall from ten to twenty times
thicker than the excessively
thin finished wall of the cell,
which will ultimately be left.
We shall understand how they
work, by supposing masons first
to pile up a broad ridge of cement,
and then to begin cutting it
away equally on both sides near
the ground, till a smooth, very
thin wall is left in the middle;
the masons always piling up the
cut-away cement, and adding fresh
cement, on the summit of the
ridge. We shall thus have a thin
wall steadily growing upward;
but always crowned by a gigantic
coping. From all the cells, both
those just commenced and those
completed, being thus crowned
by a strong coping of wax, the
bees can cluster and crawl over
the comb without injuring the
delicate hexagonal walls, which
are only about one four-hundredth
of an inch in thickness; the
plates of the pyramidal basis
being about twice as thick. By
this singular manner of building,
strength is continually given
to the comb, with the utmost
ultimate economy of wax.
It seems at first to add to
the difficulty of understanding
how the cells are made, that
a multitude of bees all work
together; one bee after working
a short time at one cell going
to another, so that, as Huber
has stated, a score of individuals
work even at the commencement
of the first cell. I was able
practically to show this fact,
by covering the edges of the
hexagonal walls of a single cell,
or the extreme margin of the
circumferential rim of a growing
comb, with an extremely thin
layer of melted vermilion wax;
and I invariably found that the
colour was most delicately diffused
by the bees as delicately as
a painter could have done with
his brush by atoms of the coloured
wax having been taken from the
spot on which it had been placed,
and worked into the growing edges
of the cells all round. The work
of construction seems to be a
sort of balance struck between
many bees, all instinctively
standing at the same relative
distance from each other, all
trying to sweep equal spheres,
and then building up, or leaving
ungnawed, the planes of intersection
between these spheres. It was
really curious to note in cases
of difficulty, as when two pieces
of comb met at an angle, how
often the bees would entirely
pull down and rebuild in different
ways the same cell, sometimes
recurring to a shape which they
had at first rejected.
When bees have a place on which
they can stand in their proper
positions for working, for instance,
on a slip of wood, placed directly
under the middle of a comb growing
downwards so that the comb has
to be built over one face of
the slip in this case the bees
can lay the foundations of one
wall of a new hexagon, in its
strictly proper place, projecting
beyond the other completed cells.
It suffices that the bees should
be enabled to stand at their
proper relative distances from
each other and from the walls
of the last completed cells,
and then, by striking imaginary
spheres, they can build up a
wall intermediate between two
adjoining spheres; but, as far
as I have seen, they never gnaw
away and finish off the angles
of a cell till a large part both
of that cell and of the adjoining
cells has been built. This capacity
in bees of laying down under
certain circumstances a rough
wall in its proper place between
two just-commenced cells, is
important, as it bears on a fact,
which seems at first quite subversive
of the foregoing theory; namely,
that the cells on the extreme
margin of wasp-combs are sometimes
strictly hexagonal; but I have
not space here to enter on this
subject. Nor does there seem
to me any great difficulty in
a single insect (as in the case
of a queen-wasp) making hexagonal
cells, if she work alternately
on the inside and outside of
two or three cells commenced
at the same time, always standing
at the proper relative distance
from the parts of the cells just
begun, sweeping spheres or cylinders,
and building up intermediate
planes. It is even conceivable
that an insect might, by fixing
on a point at which to commence
a cell, and then moving outside,
first to one point, and then
to five other points, at the
proper relative distances from
the central point and from each
other, strike the planes of intersection,
and so make an isolated hexagon:
but I am not aware that any such
case has been observed; nor would
any good be derived from a single
hexagon being built, as in its
construction more materials would
be required than for a cylinder.
As natural selection acts only
by the accumulation of slight
modifications of structure or
instinct, each profitable to
the individual under its conditions
of life, it may reasonably be
asked, how a long and graduated
succession of modified architectural
instincts, all tending towards
the present perfect plan of construction,
could have profited the progenitors
of the hive-bee? I think the
answer is not difficult: it is
known that bees are often hard
pressed to get sufficient nectar;
and I am informed by Mr. Tegetmeier
that it has been experimentally
found that no less than from
twelve to fifteen pounds of dry
sugar are consumed by a hive
of bees for the secretion of
each pound of wax; so that a
prodigious quantity of fluid
nectar must be collected and
consumed by the bees in a hive
for the secretion of the wax
necessary for the construction
of their combs. Moreover, many
bees have to remain idle for
many days during the process
of secretion. A large store of
honey is indispensable to support
a large stock of bees during
the winter; and the security
of the hive is known mainly to
depend on a large number of bees
being supported. Hence the saving
of wax by largely saving honey
must be a most important element
of success in any family of bees.
Of course the success of any
species of bee may be dependent
on the number of its parasites
or other enemies, or on quite
distinct causes, and so be altogether
independent of the quantity of
honey which the bees could collect.
But let us suppose that this
latter circumstance determined,
as it probably often does determine,
the numbers of a humble-bee which
could exist in a country; and
let us further suppose that the
community lived throughout the
winter, and consequently required
a store of honey: there can in
this case be no doubt that it
would be an advantage to our
humble-bee, if a slight modification
of her instinct led her to make
her waxen cells near together,
so as to intersect a little;
for a wall in common even to
two adjoining cells, would save
some little wax. Hence it would
continually be more and more
advantageous to our humble-bee,
if she were to make her cells
more and more regular, nearer
together, and aggregated into
a mass, like the cells of the
Melipona; for in this case a
large part of the bounding surface
of each cell would serve to bound
other cells, and much wax would
be saved. Again, from the same
cause, it would be advantageous
to the Melipona, if she were
to make her cells closer together,
and more regular in every way
than at present; for then, as
we have seen, the spherical surfaces
would wholly disappear, and would
all be replaced by plane surfaces;
and the Melipona would make a
comb as perfect as that of the
hive-bee. Beyond this stage of
perfection in architecture, natural
selection could not lead; for
the comb of the hive-bee, as
far as we can see, is absolutely
perfect in economising wax.
Thus, as I believe, the most
wonderful of all known instincts,
that of the hive-bee, can be
explained by natural selection
having taken advantage of numerous,
successive, slight modifications
of simpler instincts; natural
selection having by slow degrees,
more and more perfectly, led
the bees to sweep equal spheres
at a given distance from each
other in a double layer, and
to build up and excavate the
wax along the planes of intersection.
The bees, of course, no more
knowing that they swept their
spheres at one particular distance
from each other, than they know
what are the several angles of
the hexagonal prisms and of the
basal rhombic plates. The motive
power of the process of natural
selection having been economy
of wax; that individual swarm
which wasted least honey in the
secretion of wax, having succeeded
best, and having transmitted
by inheritance its newly acquired
economical instinct to new swarms,
which in their turn will have
had the best chance of succeeding
in the struggle for existence.
No doubt many instincts of
very difficult explanation could
be opposed to the theory of natural
selection, cases, in which we
cannot see how an instinct could
possibly have originated; cases,
in which no intermediate gradations
are known to exist; cases of
instinct of apparently such trifling
importance, that they could hardly
have been acted on by natural
selection; cases of instincts
almost identically the same in
animals so remote in the scale
of nature, that we cannot account
for their similarity by inheritance
from a common parent, and must
therefore believe that they have
been acquired by independent
acts of natural selection. I
will not here enter on these
several cases, but will confine
myself to one special difficulty,
which at first appeared to me
insuperable, and actually fatal
to my whole theory. I allude
to the neuters or sterile females
in insect-communities: for these
neuters often differ widely in
instinct and in structure from
both the males and fertile females,
and yet, from being sterile,
they cannot propagate their kind.
The subject well deserves to
be discussed at great length,
but I will here take only a single
case, that of working or sterile
ants. How the workers have been
rendered sterile is a difficulty;
but not much greater than that
of any other striking modification
of structure; for it can be shown
that some insects and other articulate
animals in a state of nature
occasionally become sterile;
and if such insects had been
social, and it had been profitable
to the community that a number
should have been annually born
capable of work, but incapable
of procreation, I can see no
very great difficulty in this
being effected by natural selection.
But I must pass over this preliminary
difficulty. The great difficulty
lies in the working ants differing
widely from both the males and
the fertile females in structure,
as in the shape of the thorax
and in being destitute of wings
and sometimes of eyes, and in
instinct. As far as instinct
alone is concerned, the prodigious
difference in this respect between
the workers and the perfect females,
would have been far better exemplified
by the hive-bee. If a working
ant or other neuter insect had
been an animal in the ordinary
state, I should have unhesitatingly
assumed that all its characters
had been slowly acquired through
natural selection; namely, by
an individual having been born
with some slight profitable modification
of structure, this being inherited
by its offspring, which again
varied and were again selected,
and so onwards. But with the
working ant we have an insect
differing greatly from its parents,
yet absolutely sterile; so that
it could never have transmitted
successively acquired modifications
of structure or instinct to its
progeny. It may well be asked
how is it possible to reconcile
this case with the theory of
natural selection?
First, let it be remembered
that we have innumerable instances,
both in our domestic productions
and in those in a state of nature,
of all sorts of differences of
structure which have become correlated
to certain ages, and to either
sex. We have differences correlated
not only to one sex, but to that
short period alone when the reproductive
system is active, as in the nuptial
plumage of many birds, and in
the hooked jaws of the male salmon.
We have even slight differences
in the horns of different breeds
of cattle in relation to an artificially
imperfect state of the male sex;
for oxen of certain breeds have
longer horns than in other breeds,
in comparison with the horns
of the bulls or cows of these
same breeds. Hence I can see
no real difficulty in any character
having become correlated with
the sterile condition of certain
members of insect-communities:
the difficulty lies in understanding
how such correlated modifications
of structure could have been
slowly accumulated by natural
selection.
This difficulty, though appearing
insuperable, is lessened, or,
as I believe, disappears, when
it is remembered that selection
may be applied to the family,
as well as to the individual,
and may thus gain the desired
end. Thus, a well-flavoured vegetable
is cooked, and the individual
is destroyed; but the horticulturist
sows seeds of the same stock,
and confidently expects to get
nearly the same variety; breeders
of cattle wish the flesh and
fat to be well marbled together;
the animal has been slaughtered,
but the breeder goes with confidence
to the same family. I have such
faith in the powers of selection,
that I do not doubt that a breed
of cattle, always yielding oxen
with extraordinarily long horns,
could be slowly formed by carefully
watching which individual bulls
and cows, when matched, produced
oxen with the longest horns;
and yet no one ox could ever
have propagated its kind. Thus
I believe it has been with social
insects: a slight modification
of structure, or instinct, correlated
with the sterile condition of
certain members of the community,
has been advantageous to the
community: consequently the fertile
males and females of the same
community flourished, and transmitted
to their fertile offspring a
tendency to produce sterile members
having the same modification.
And I believe that this process
has been repeated, until that
prodigious amount of difference
between the fertile and sterile
females of the same species has
been produced, which we see in
many social insects.
But we have not as yet touched
on the climax of the difficulty;
namely, the fact that the neuters
of several ants differ, not only
from the fertile females and
males, but from each other, sometimes
to an almost incredible degree,
and are thus divided into two
or even three castes. The castes,
moreover, do not generally graduate
into each other, but are perfectly
well defined; being as distinct
from each other, as are any two
species of the same genus, or
rather as any two genera of the
same family. Thus in Eciton,
there are working and soldier
neuters, with jaws and instincts
extraordinarily different: in
Cryptocerus, the workers of one
caste alone carry a wonderful
sort of shield on their heads,
the use of which is quite unknown:
in the Mexican Myrmecocystus,
the workers of one caste never
leave the nest; they are fed
by the workers of another caste,
and they have an enormously developed
abdomen which secretes a sort
of honey, supplying the place
of that excreted by the aphides,
or the domestic cattle as they
may be called, which our European
ants guard or imprison.
It will indeed be thought that
I have an overweening confidence
in the principle of natural selection,
when I do not admit that such
wonderful and well-established
facts at once annihilate my theory.
In the simpler case of neuter
insects all of one caste or of
the same kind, which have been
rendered by natural selection,
as I believe to be quite possible,
different from the fertile males
and females, in this case, we
may safely conclude from the
analogy of ordinary variations,
that each successive, slight,
profitable modification did not
probably at first appear in all
the individual neuters in the
same nest, but in a few alone;
and that by the long-continued
selection of the fertile parents
which produced most neuters with
the profitable modification,
all the neuters ultimately came
to have the desired character.
On this view we ought occasionally
to find neuter-insects of the
same species, in the same nest,
presenting gradations of structure;
and this we do find, even often,
considering how few neuter-insects
out of Europe have been carefully
examined. Mr F. Smith has shown
how surprisingly the neuters
of several British ants differ
from each other in size and sometimes
in colour; and that the extreme
forms can sometimes be perfectly
linked together by individuals
taken out of the same nest: I
have myself compared perfect
gradations of this kind. It often
happens that the larger or the
smaller sized workers are the
most numerous; or that both large
and small are numerous, with
those of an intermediate size
scanty in numbers. Formica flava
has larger and smaller workers,
with some of intermediate size;
and, in this species, as Mr F.
Smith has observed, the larger
workers have simple eyes (ocelli),
which though small can be plainly
distinguished, whereas the smaller
workers have their ocelli rudimentary.
Having carefully dissected several
specimens of these workers, I
can affirm that the eyes are
far more rudimentary in the smaller
workers than can be accounted
for merely by their proportionally
lesser size; and I fully believe,
though I dare not assert so positively,
that the workers of intermediate
size have their ocelli in an
exactly intermediate condition.
So that we here have two bodies
of sterile workers in the same
nest, differing not only in size,
but in their organs of vision,
yet connected by some few members
in an intermediate condition.
I may digress by adding, that
if the smaller workers had been
the most useful to the community,
and those males and females had
been continually selected, which
produced more and more of the
smaller workers, until all the
workers had come to be in this
condition; we should then have
had a species of ant with neuters
very nearly in the same condition
with those of Myrmica. For the
workers of Myrmica have not even
rudiments of ocelli, though the
male and female ants of this
genus have well-developed ocelli.
I may give one other case:
so confidently did I expect to
find gradations in important
points of structure between the
different castes of neuters in
the same species, that I gladly
availed myself of Mr F. Smith's
offer of numerous specimens from
the same nest of the driver ant
(Anomma) of West Africa. The
reader will perhaps best appreciate
the amount of difference in these
workers, by my giving not the
actual measurements, but a strictly
accurate illustration: the difference
was the same as if we were to
see a set of workmen building
a house of whom many were five
feet four inches high, and many
sixteen feet high; but we must
suppose that the larger workmen
had heads four instead of three
times as big as those of the
smaller men, and jaws nearly
five times as big. The jaws,
moreover, of the working ants
of the several sizes differed
wonderfully in shape, and in
the form and number of the teeth.
But the important fact for us
is, that though the workers can
be grouped into castes of different
sizes, yet they graduate insensibly
into each other, as does the
widely-different structure of
their jaws. I speak confidently
on this latter point, as Mr Lubbock
made drawings for me with the
camera lucida of the jaws which
I had dissected from the workers
of the several sizes.
With these facts before me,
I believe that natural selection,
by acting on the fertile parents,
could form a species which should
regularly produce neuters, either
all of large size with one form
of jaw, or all of small size
with jaws having a widely different
structure; or lastly, and this
is our climax of difficulty,
one set of workers of one size
and structure, and simultaneously
another set of workers of a different
size and structure; a graduated
series having been first formed,
as in the case of the driver
ant, and then the extreme forms,
from being the most useful to
the community, having been produced
in greater and greater numbers
through the natural selection
of the parents which generated
them; until none with an intermediate
structure were produced.
Thus, as I believe, the wonderful
fact of two distinctly defined
castes of sterile workers existing
in the same nest, both widely
different from each other and
from their parents, has originated.
We can see how useful their production
may have been to a social community
of insects, on the same principle
that the division of labour is
useful to civilised man. As ants
work by inherited instincts and
by inherited tools or weapons,
and not by acquired knowledge
and manufactured instruments,
a perfect division of labour
could be effected with them only
by the workers being sterile;
for had they been fertile, they
would have intercrossed, and
their instincts and structure
would have become blended. And
nature has, as I believe, effected
this admirable division of labour
in the communities of ants, by
the means of natural selection.
But I am bound to confess, that,
with all my faith in this principle,
I should never have anticipated
that natural selection could
have been efficient in so high
a degree, had not the case of
these neuter insects convinced
me of the fact. I have, therefore,
discussed this case, at some
little but wholly insufficient
length, in order to show the
power of natural selection, and
likewise because this is by far
the most serious special difficulty,
which my theory has encountered.
The case, also, is very interesting,
as it proves that with animals,
as with plants, any amount of
modification in structure can
be effected by the accumulation
of numerous, slight, and as we
must call them accidental, variations,
which are in any manner profitable,
without exercise or habit having
come into play. For no amount
of exercise, or habit, or volition,
in the utterly sterile members
of a community could possibly
have affected the structure or
instincts of the fertile members,
which alone leave descendants.
I am surprised that no one has
advanced this demonstrative case
of neuter insects, against the
well-known doctrine of Lamarck.
Summary. I have endeavoured
briefly in this chapter to show
that the mental qualities of
our domestic animals vary, and
that the variations are inherited.
Still more briefly I have attempted
to show that instincts vary slightly
in a state of nature. No one
will dispute that instincts are
of the highest importance to
each animal. Therefore I can
see no difficulty, under changing
conditions of life, in natural
selection accumulating slight
modifications of instinct to
any extent, in any useful direction.
In some cases habit or use and
disuse have probably come into
play. I do not pretend that the
facts given in this chapter strengthen
in any great degree my theory;
but none of the cases of difficulty,
to the best of my judgment, annihilate
it. On the other hand, the fact
that instincts are not always
absolutely perfect and are liable
to mistakes; that no instinct
has been produced for the exclusive
good of other animals, but that
each animal takes advantage of
the instincts of others; that
the canon in natural history,
of 'natura non facit saltum'
is applicable to instincts as
well as to corporeal structure,
and is plainly explicable on
the foregoing views, but is otherwise
inexplicable, all tend to corroborate
the theory of natural selection.
This theory is, also, strengthened
by some few other facts in regard
to instincts; as by that common
case of closely allied, but certainly
distinct, species, when inhabiting
distant parts of the world and
living under considerably different
conditions of life, yet often
retaining nearly the same instincts.
For instance, we can understand
on the principle of inheritance,
how it is that the thrush of
South America lines its nest
with mud, in the same peculiar
manner as does our British thrush:
how it is that the male wrens
(Troglodytes) of North America,
build 'cock-nests,' to roost
in, like the males of our distinct
Kitty-wrens, a habit wholly unlike
that of any other known bird.
Finally, it may not be a logical
deduction, but to my imagination
it is far more satisfactory to
look at such instincts as the
young cuckoo ejecting its foster-brothers,
ants making slaves, -- the larvae
of ichneumonidae feeding within
the live bodies of caterpillars,
not as specially endowed or created
instincts, but as small consequences
of one general law, leading to
the advancement of all organic
beings, namely, multiply, vary,
let the strongest live and the
weakest die. |