The Origin of Species

by Charles Darwin

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.