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 t
heir 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 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 precious 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.