Instinct should probably have been dealt with in the previous chapters; but I have thought it more fitting to treat the subject separately, as an instinct so wonderful as that of the cell-building bees may well have seemed to many a reader sufficient difficulty to overthrow my theory. I must say in advance that I have nothing to do with the origin of the basic spiritual forces, nor with that of life itself. We are concerned only with the difference in instinct and in the other mental faculties of animals in the same class.
I will not try to give a definition of the word. It would be easy to show that quite different mental faculties are commonly conceived under this name.[p. 235]But everyone knows what I mean when I say that instinct causes the cuckoo to wander and lay its eggs in other people's nests. When an action which requires experience, even on our part, is performed by an animal, and especially a very young animal, without any experience, and when it is performed in the same way by many animals without their knowing its purpose, so it is usually called an instinctive action. I could, however, show that none of these characters of instinct are general. A small dose of judgment, or common sense, as PIERRE HUBER puts it, often comes into play, even with animals very low on the scale of nature.
F RIEDRICH C UVIERand various ancient metaphysicians have likened instinct to habit. This comparison seems to me to give a very accurate demonstration of the limits of the mind within which the action is accomplished, but not of its origin. How unconsciously some of our actions are performed, not infrequently in direct opposition to our conscious will! But they can be altered by the will or mind. Habits easily combine with other habits or with certain periods of time and states of the body. Once accepted, they are often granted for life. Many other resemblances between instincts and habits could be pointed out. As in the repetition of a well-known song, so also in instinct, one action follows another by a kind of rhythm. When a man is interrupted in singing, or in pronouncing words he has learned by heart, he is usually obliged to step back a little in order to regain the train of thought. That's how P.HUBER also in a species of caterpillar when busy making its very complex tissue; he took them out after the same z. For example, when the last sixth was finished and he placed it in another one that was only completed to the third sixth, she simply finished the third, fourth and fifth part again[p. 236]with the sixth on. But he took it from a z. B. finished fabric up to the third part and put it into a finished up to the sixth part, so that she found her work already done for the most part, she was very far from feeling this advantage and was very embarrassed about this state of affairs Work again from the third stage, where she had left such in her own fabric, and from there sought to complete the already finished work.
Now, if it could be shown, as I think I can in some cases, that a manner of action acquired through habit is hereditary to offspring, then what was originally habit would no longer be distinguishable from instinct. If MOZARTinstead of playing the pianoforte with wonderful little skill at the age of three, without any prior practice having struck up a melody, one might truthfully say that he did this instinctively. But it would be a very serious error to suppose that the majority of the instincts were acquired by habit during one generation, and then passed on to succeeding generations. It can be accurately demonstrated that the most wonderful instincts known to us, such as those of the hive-bees and many ants, could not possibly have been acquired in such a time.
It is generally acknowledged that instincts are as important as body formation to the prosperity of any species in its present conditions of existence. If the living conditions of a species change, it is at least possible that even slight changes in its instincts would be of service to it. If it can now be shown that instincts vary, however little, then I can see no difficulty in assuming that natural selection preserves even slight variations in instinct and increases it to an advantageous degree through constant accumulation. In this way, I believe, all instincts, including the most complex and wonderful, may have arisen. How variations in bodily structure are induced and increased by use and habit,[p. 237]On the other hand, if they can be diminished and lost entirely through disuse, the same is undoubtedly true of the instincts. But I believe that the effects of habit are of quite secondary importance to the effects of natural selection upon so-called accidental variations of instinct, i. H. to variations due to unknown causes causing slight deviations in bodily structure.
No composite instinct can be produced by Natural Selection but by the slow and gradual accumulation of many slight and useful variations. Here, as in the case of the formation of the body, we would not have to go through the real transitional stages in nature, which the composite instinct has passed through to its present perfection and which in each species could only be discovered in its straight line predecessor but to find some traces of such gradations in the lateral lines of ancestry, or at least to show that any gradations are possible; and we are certainly capable of that. Although the instincts are almost exclusively found in Europe and North Americaliving animals have been observed more closely and those of the extinct animals are completely unknown to us, I was astonished to find how quite general gradations up to the instincts of the most complex species can be discovered. Changes of instincts may sometimes be facilitated by the same species possessing different instincts in different periods or seasons of life, or by being placed under different external conditions of life, in which cases either one or the other will be obtained by natural breeding. Examples of such diversity of instinct can be found in nature.
Now, as in body formation, according to my theory, the instinct of each species is useful to that species, and never, as far as we know, for the exclusive benefit of other species. One of the clearest examples I know of of animals apparently doing something for the sheer good of others is provided by the aphids, in that, like Huber, they first[p. 238]remarked, voluntarily left their sweet excretions to the ants. That they do this voluntarily is evident from the following facts. I removed all the ants from a group of about twelve aphids on a dock plant and prevented their gathering for several hours. After that time I noticed that the aphids had the need of excretion. I watched them for a while through a magnifying glass: but not one made an excretion. I then stroked and tickled them with a hair in the same way ants do with their antennae, but no excretion ensued. Now I admitted an ant, and from its reluctance to be driven back by the aphids seemed to show that it had at once realized what a rich pleasure awaited it. She then began to feel with her antennae the abdomen of first one and then another aphid, each of which, as it felt the touch of the antennae, immediately raised its abdomen and excreted a clear drop of sweet liquid, which immediately fell from the ant was sucked in. Even very young aphids treated in this way showed that their behavior was instinctive and not the result of experience. After H that their behavior was instinctive and not the result of experience. After H that their behavior was instinctive and not the result of experience. After HThe aphids show no aversion to the ants, and in the absence of these they are forced to eject their excretions. Now as the excretion is exceedingly sticky, it is probably of use to the aphids that it should be removed; and so this excretion is probably not aimed at the exclusive advantage of the ants. Though I do not believe that any animal in the world does anything for the exclusive benefit of another species, yet every species seeks to take advantage of the instincts of others, and takes advantage of the weaker constitution of others. Thus, in a few cases, certain instincts cannot be regarded as completely perfect, which I must refrain from explaining here in detail.
As many examples as possible should be given to show how in the state of nature a certain degree of[p. 239]Variation in the instincts, and the inheritance of such variations, is indispensable to the action of natural selection, but want of space prevents me from doing it. I can only affirm that instincts certainly vary, e.g. B. the wandering instinct may vary in extent and direction, or may cease altogether. So it is with the nests of birds, which change partly according to the place chosen for them, according to the natural and warm conditions of the inhabited region, but also often for completely unknown reasons. Thus A UDUBON has some very curious instances of differences in the nests of the same species of birds, according as they are in the north or south of the United Stateslive shared. Why, it has been asked, has not the nature of the bee, if instinct is changeable, conferred faculty of employing other materials where wax is wanting? But what other materials could the bees use? I have seen them use and process wax mixed with cooking oil and fat. A NDREW K NIGHTsaw his bees, instead of busy collecting pollen, using cement made of wax and turpentine, with which debarked trees had been coated. Finally, bees have lately been observed, which, instead of visiting flowers for the dust of their seeds, willingly use a quite different substance, viz., oatmeal. —Fear of any particular enemy is certainly an instinctive quality, as has occasion to be seen in birds still in the nest, though it is increased by experience, and by perception of fear of the same enemy in other animals. Animals on remote little islands are not afraid of man, and, as I have shown elsewhere, are slow to fear him; and so do we also in EnglandIt is true that the large birds, because they are more pursued by man, fear him much more than the small ones. We may confidently attribute the greater shyness of large birds to this cause, for on uninhabited islands the large ones are no shyer than the small ones; and the magpie[p. 240]so timid in England , is as tame in Norway as the crow (Corvus cornix) in Egypt .
That the tempers of the individuals of a species in general, even when born in the wild, be extremely varied, can be proved by many facts. Also, in some species examples could be given of accidental and strange habits, which, if useful to the species, might, by natural selection, give rise to quite new instincts. I know well that these general statements, without particular facts to support them, will make but a feeble impression on the mind of the reader, but I can only repeat my assurance that I do not speak without good evidence.
The possibility, or even the probability, of inheriting variations of instinct in the state of nature will become more apparent by considering some cases in domesticated animals. We are thereby enabled to see what comparative influence habituation and the breeding of so-called accidental deviations have exerted in modifying the mental faculties of our domestic animals. A number of odd and well-established instances may be given of the inheritance of all shades of disposition, of taste, or of the inclination to the strangest pranks, in connection with signs of spirit, or with certain periodic conditions. The various dog breeds provide us with well-known evidence of this. So there is no doubt (and I have seen a striking case of this kind myself) that young pointers sometimes pull before other dogs when they are first taken out. Thus the stalking of partridges is certainly often hereditary in dogs of the breed most preferably used for this purpose, just as young sheep-dogs are apt to circle the flock instead of running beside it. I cannot see that these actions are essentially different from those of instinct; for the young dogs act without experience, one almost like the other in the same breed, and without knowing the purpose of the action. Because the young pointing dog like young shepherd dogs are inclined to circle the herd instead of running alongside. I cannot see that these actions are essentially different from those of instinct; for the young dogs act without experience, one almost like the other in the same breed, and without knowing the purpose of the action. Because the young pointing dog like young shepherd dogs are inclined to circle the herd instead of running alongside. I cannot see that these actions are essentially different from those of instinct; for the young dogs act without experience, one almost like the other in the same breed, and without knowing the purpose of the action. Because the young pointing dog[p. 241]no more does he know that by standing he is serving the purposes of his master than the cabbage butterfly knows why it lays its eggs on a cabbage leaf. Suppose we saw a kind of wolf which, while young and untrained, would stand motionless like a statue when scenting its prey, and then creep slowly towards it with a peculiar bearing, or another kind of wolf which, instead of leaping at a herd of deer, circled it and so drifted to a distant point, we should certainly ascribe this behavior to instinct. Tame instincts, as they might be called, are certainly much less fixed and immutable than the natural ones; for they have been marked by much less strict breeding and have been inherited for a far shorter time under less stable living conditions.
How strictly these "tame instincts", habits and tendencies are inherited and how wondrously they sometimes mix, is shown quite clearly when different dog breeds are crossed with one another. Thus a cross with bullbiters has influenced the courage and tenacity of the greyhound for many generations, and a cross with the greyhound has transmitted to a whole family of shepherds the tendency to pursue hares. These tame instincts, thus tested by crossing, are like natural instincts, which are similarly strangely combined, so that traces of the instincts of both parents are preserved for a long time. This is how L E R OY describesa dog whose grandfather was a wolf; this hound betrayed the traces of his savage parentage in only one way, by never coming straight at him when called by his master.
Tame instincts are sometimes referred to as actions which become hereditary merely through a long-continued and enforced habit; I believe, however, that this is not correct. Certainly nobody has ever thought of or tried to teach the tumble dove to tumble, which to my knowledge even young pigeons do, which others never do[p. 242]have seen tumble. One can imagine that a single pigeon once showed a tendency to this peculiar manner of movement, and that then, as a result of careful and long-continued breeding, the tumblers gradually became what they are now; and as I understand from Mr B RENT there is at GlasgowHouse Tumblers, which cannot fly 18 inches without flipping upside down once. In the same way it is difficult to doubt whether anyone ever thought of training a dog to point unless an individual had of himself shown an inclination to do so, and this is known to happen at times, as I once did watching a dachshund; the "standing" is probably, as some have thought, only an increased pause of an animal preparing to pounce on its prey. Once a first beginning of standing had been shown, methodical selection and the hereditary effect of compulsory training in each succeeding generation may soon have completed the work: and unconscious selection is always in action, since everyone, though without any intention of creating an improved breed, likes to procure those dogs which are the best at pointing and hunting. On the other hand, habit has sufficed in some cases. Hardly any animal is generally more difficult to tame than the young of the wild rabbit, and no animal more tame than the young of the tame rabbit; and yet I can scarcely believe that the domestic rabbits were bred for tameness, but rather suspect that we have to attribute the entire hereditary change from extreme wildness to extreme tameness solely to habit and long-continued close confinement. However, like that Hardly any animal is generally more difficult to tame than the young of the wild rabbit, and no animal more tame than the young of the tame rabbit; and yet I can scarcely believe that the domestic rabbits were bred for tameness, but rather suspect that we have to attribute the entire hereditary change from extreme wildness to extreme tameness solely to habit and long-continued close confinement. However, like that Hardly any animal is generally more difficult to tame than the young of the wild rabbit, and no animal more tame than the young of the tame rabbit; and yet I can scarcely believe that the domestic rabbits were bred for tameness, but rather suspect that we have to attribute the entire hereditary change from extreme wildness to extreme tameness solely to habit and long-continued close confinement. However, like that that we have to attribute the entire hereditary change from extreme wildness to extreme tameness solely to habit and long-continued close confinement. However, like that that we have to attribute the entire hereditary change from extreme wildness to extreme tameness solely to habit and long-continued close confinement. However, like thatFrench translators of this book remarked that it was precisely the tamest rabbits, because they were the least troublesome, that were kept the most often, so that breeding would have come into play in this case too.
Natural instincts are lost in captivity; one sees a curious example of this in those[p. 243]Poultry breeds that rarely or never become "broody" [26] , i. H. never ask to sit on their balls. Daily habit alone prevents us from seeing how greatly and how generally the mental faculties of our domestic animals have been altered by domestication. There can be little doubt that man's love has passed to the dog as an instinct. All the wolves, foxes, jackals, and cats, when tamed, are very eager to attack fowl, sheep, and pigs, and the same tendency has been incurably shown in such dogs brought young to us from countries where as in Tierra del Fuego and in Australiathe savages do not keep those domestic animals. And how seldom, on the other hand, is it necessary to wean our civilized dogs, even when young, from attacking those animals. True, they sometimes make such an attack, and are then beaten and, if that doesn't help, finally carried away—so that habit and probably some breeding have worked together to instill in our dogs their hereditary civilisation. On the other hand, young chickens, entirely from habit, have lost the fear of dogs and cats which no doubt their original instincts no doubt possessed; because I hear from Capt. H UTTON that the boys of the East IndianProgenitor of this species (Gallus Bankiva), though hatched from an ordinary hen, are exceedingly fierce at first. And so it is with the young phasans from eggs hatched in England by a domestic hen. And yet the chickens have by no means lost all fear, only the fear of dogs and cats; for as soon as the hen warns them of danger by clucking, all (especially young Welsh hens) run to get under their protection, or to hide themselves in the grass and thickets, the latter apparently with instinctive intent, as we do with wild ground -birds see to their mother[p. 244] to make it possible to fly away. Of course, this instinct, which is left behind in our young hens, is quite useless when tamed, because the mother hen has usually lost the ability to fly through disuse.
From this it may be concluded that tame instincts have been acquired and wild instincts have been lost, partly through custom and partly through the action of man, which through many successive generations has produced peculiar mental tendencies and faculties which, in our ignorance, at first only arose so-called coincidence, accumulated and increased through breeding. In some cases forced habit has sufficed to bring about such hereditary alteration of mental qualities; in others nothing has been accomplished by forced discipline, and all has been effected only by unconscious or methodical discipline; but in most cases both probably worked together.
A closer consideration of a few instances will perhaps best serve to illustrate how instincts in the state of nature have been modified by selection. From the large number of cases which I will have collected and will have to discuss in my later work, I will only emphasize three cases, namely the instinct which drives the cuckoo to lay its eggs in other people's nests, the instinct of the ants to make slaves, and the cellular drive of honey bees; the last two named have rightly been described by naturalists as the two most wonderful of all known instincts.
It is now commonly assumed that the immediate and fundamental cause of the cuckoo's instinct to lay its eggs in other's nests is that they do not come to maturity in succession every day, but only every second or third day, so that, if the cuckoo had to build its own nest and perch on its own eggs, the first eggs would either remain unincubated for a time, or eggs and young birds of different ages together in the same nest[p. 245]would have to come [27] . If this were the case, however, the processes of laying and hatching would have to be unduly long, and the young birds hatched first would probably be fed by the male alone. But the American cuckoo finds itself in the same position, and yet it makes its own nest and lays its eggs in it one by one, and its young hatch at the same time. It has been asserted that the American cuckoo sometimes lays its eggs in other people's nests, but according to Dr. Brewer'sreliable guarantee in these things it is a mistake. Notwithstanding this, I could give several other instances of birds sometimes laying their eggs in other people's nests. Suppose now that the progenitor of our European cuckoo has the habits of the Americanhad, but sometimes laid an egg in another bird's nest. If the old bird benefited from this occasional custom, or the young grew stronger by the erroneous instinct of a strange mother, than he would have grown under the care of his own mother, who is overloaded with the simultaneous care of eggs and young of different ages would have been and would have had to wander by himself at a very tender age; so either the old man or the young man who was cared for at someone else's expense won. By analogy I would then like to think that, as a result of heredity, the youngster thus agitated is more apt to imitate its mother's chance and deviant actions, and also to lay its eggs in strangers' nests, and thus obtain stronger offspring. By a continued process of this kind the whimsical instinct of the cuckoo might, in my opinion, have arisen. However, I want to add that after Dr. GRAY et al. a. Observers of the European Cuckoo[p. 246]but has by no means lost all maternal love and care for his own offspring.
The custom of occasionally laying its eggs in foreign nests of the same or another species is not altogether uncommon among gallinaceous birds; and Diess perhaps explains the origin of a peculiar instinct in the neighboring group of ostrich-like birds. For several ostriches, at least of the American species, unite to lay first some eggs in one nest, and then in another; and these are hatched by the males. The fact that these hens lay a large number of eggs at intervals of two or three days will probably be taken into account in explaining this habit. However, that custom is with the Americanostriches not very developed; for there, too, lies such an astonishing quantity of eggs scattered over the plain, that I was able, on the hunt, to take up no less than 20 abandoned and spoiled eggs in one day.
Some bees parasitize and lay their eggs in the nests of other bee species. This is even more remarkable than with the cuckoo; for these bees have not only altered their instincts, but also their structure in accordance with their parasitic habits, viz., not possessing the apparatus for collecting pollen, which they would need if they had to store up food for their own brood. Some species of insects parasitize on other species in the manner of the Sphegid, and Mr. F ABREhas lately shown good reason to believe that, although Tachytes nigra commonly makes its own burrow, and stores therein live but paralyzed prey for the food of its own larvae, it still does when it makes an already made and stocked burrow of another sphex finds, takes possession of it and, as a result of this opportunity, becomes a parasite. In this case, as in the supposed example of the cuckoo, there is no impediment to natural selection,[p. 247]to make the occasional custom a permanent one, if it is useful to the species, and if the other species of insects, whose nest and stores of food it treacherously appropriates, are not consequently exterminated.
Instinct to make slaves .) This natural drive was first described in Formica (Poliergus) rufescens by P ETER H UBERobserved, an even better observer than his famous father had been. This ant is absolutely dependent on its slaves, without whose help the species would perish completely within a year. The males and fertile females do not work. The working or barren females, on the other hand, although very brave and energetic in capturing slaves, do nothing else. They are unable to make their own nests or feed their own young. When the old nest is found unsuitable, and emigration becomes necessary, the slaves decide, and then drag their masters away between their jaws. These last are so utterly helpless that, as H UBER thirty of whom, without slaves, were locked together with plenty of the best fodder and at the same time with their larvae and pupae to spur them on to activity, they did not even feed themselves, and most of them died of starvation. H UBER then brought in a single slave (Formica fusca) who immediately went to work feeding and rescuing those who survived, making some cells, tending the larvae and putting everything in order. What can be more extraordinary than these well-established facts? Had one not known of some other slave-making ants, it would have been a hopeless attempt to imagine how so wonderful an instinct could flourish to such perfection.
Another species of ant, Formica sanguinea, was also first recognized by Huber as a slavemaker . It occurs in the southern part of England , where its habits have been observed by HF S MITH of the British Museum , to whom I am grateful for his communications on this and other subjects[p. 248]am very connected. Though having full confidence in the assurances of the two naturalists mentioned, I could not go about the matter without some doubt, and it may well be excused if one should think of such an extraordinary and ugly instinct as that of making slaves , cannot immediately believe. I will therefore relate in a few details what I have observed myself. I opened fourteen clusters of nests of Formica sanguinea and found some slaves in all of them. Males and fertile females of the slave species (F. fusca) are found only in their own community and have never been found in clusters of F. sanguinea. The slaves are black, and no more than half the height of their masters, so that the contrast in their appearance is at once striking. When the crowd is only a little disturbed, the slaves sometimes come out, and like their masters show themselves much alarmed and ready to defend themselves. But if the heap is so shattered that larvae and pupae are exposed, the slaves and their masters make every effort to drag them to a safe place. From this it is clear that the slaves feel quite at home. During the months of June and July I have been in the counties for three consecutive years From this it is clear that the slaves feel quite at home. During the months of June and July I have been in the counties for three consecutive years From this it is clear that the slaves feel quite at home. During the months of June and July I have been in the counties for three consecutive yearsSurrey and Sussex watched several such anthills for hours and never saw a slave go in or out. As during these months the slaves are few, I thought they would behave differently if they were in greater numbers; but also Mr. S MITH informs me that he takes the nests at different hours during the months of May, June and August in Surrey as in Hampshireand, although the slaves are numerous in August, has never seen any of them go in or out. He therefore regards them merely as domestic slaves. On the other hand, one sees their masters constantly bringing nest-building materials and fodder of all kinds. In July of this year, however, I came to a church with an unusually strong slave estate, and saw a few slaves mingled with their masters[p. 249]Leaving nest, and taking them the same way to a Scots pine twenty-five cubits away, and running up the trunk, probably to look for aphids or scale-lice. According to Huber , who had ample opportunity of observation, in Switzerland the slaves usually work with their masters at the making of the nest, and they alone open and close the gates in the morning and evening hours; however, as H UBER expressly affirms, their main business is foraging for aphids. This difference in the prevailing habits of master and slave in two places may depend only on that in Switzerlandthe slaves are more numerous to capture than in England .
Fortunately, one day I noticed a migration of F. sanguinea from one heap to another, and it was a very interesting sight to see the masters carefully dragging their slaves away between their jaws, instead of being carried by them themselves, as was the case with F. rufescens is the case. Another day my attention was attracted by about two dozen ants of the slave-making kind, which were visiting the same spot, but evidently not for the sake of food. On their approach they were repelled by an independent colony of the slave-giving species, F. fusca, so that sometimes up to three of these latter were attached to the legs of a F. sanguinea. This last ruthlessly slew her smaller opponents, and dragged their corpses for food to her nest twenty-nine cubits distant; but she was prevented from taking dolls to raise them into slaves. I then took a small number of pupae from another group of F. fusca and placed them in a bare spot near the battleground. These were eagerly seized and carried away by the tyrants, who perhaps imagined that they had finally been victors in the last battle.
At the same time I laid down in the same place a batch of Formica flava pupae with a few mature ants of this yellow species still clinging to fragments of their nest. This species also sometimes, but seldom, becomes a slave[p. 250]made, like Mr. S MITH has described. Although small, this species is very courageous, and I have seen it attack other ants with wild impetuosity. Once, to my astonishment, I found under a rock an independent colony of Formica flava, still below a nest of the slave-making F. sanguinea; and as I had happened to disturb both nests, the small species attacked its larger neighbor with astonishing courage. I was now curious to know whether F. sanguinea would be able to distinguish the pupae of F. fusca, which it commonly uses for slave breeding, from those of the small enraged F. flava, which it seldom takes in captivity. and it soon appeared that she had this discernment; for I saw her eagerly and instantaneously pounce upon the pupae of F. fusca, while she seemed greatly frightened, when she came across the pupae or even the soil from the nest of F. flava and ran away quickly. But after about a quarter of an hour, shortly after all the little yellow ants had left the spot, they got courage and picked up these pupae too.
One evening I visited another community of F. sanguinea and found a number of them on their way home and at the entrance to their nest, dragging corpses and many pupae of F. fusca with them, not just migrating. I traced a line of ants laden with prey, forty yards long, to a dense grove of scrub, where I saw the last individual of F. sanguinea come out laden with a pupa; but I could not find the destroyed nest in the dense heath, although it cannot have been far off, as two or three individuals of F. fusca ran about in the greatest excitement and one hung motionless at the top of a heath branch: all with their own dolls in their mouths, a picture of despair over their destroyed homeland.
These are the facts which I can relate, though not needing my confirmation, of the wondrous slave-making instinct. First is the great contrast between the instinctive habits of F. sanguinea[p. 251]and the continental F. rufescens. This last does not build its own nest, does not determine its own migrations, does not gather food for itself and its brood, and cannot even feed by itself; she is absolutely dependent on her numerous slaves. The F. sanguinea, on the other hand, keeps far fewer slaves, especially in the first part of summer; the masters determine when and where a new nest is to be built; and when they wander, the masters drag the slaves. In Switzerland , as in England , the slaves seem to be charged exclusively with the care of the brood, and the masters alone go about catching slaves. In Switzerland masters and slaves work together to procure nest-building materials; both, and yet preferably, visit the slaves and milk, as it may be called, their aphids, and both gather food for the community. In England the masters usually leave the nest alone to gather building materials and fodder for themselves, their larvae and slaves, so that they receive much less service from their slaves here than in Switzerland .
I will not presume to guess how the instinct of F. sanguinea developed. But as ants, which are not slave-makers, as we have seen, accidentally drag home pupae of other species scattered about their nest, perhaps to use them for food, such pupae may sometimes still develop there, and thus unintentionally im Home-bred strangers may then follow their own instincts and work what they can. If their presence proves useful to the species which has taken them up, and is more suited to capturing workers than raising them, the originally fortuitous custom of collecting foreign pupae for food may be reinforced by natural selection, and finally for quite a different purpose To educate slaves to be permanently attached.[p. 252] Received help in England than in Switzerland, I have no hesitation in assuming that natural selection then altered this instinct and, always assuming that every modification of the species had been useful, gradually modified it to such an extent that at last an ant species arose in such a way contemptuous dependence on their own slaves, as is F. rufescens.
Hive Bee Cell Building Instinct.) I do not intend to go into minute detail on this subject, but will confine myself to giving a sketch of the results to which I have arrived. It would have to be a dull man not to fall into enthusiastic astonishment upon examining the excellent structure of a honeycomb, so wondrously adapted to its purpose. We hear from mathematicians that the bees have practically solved a difficult problem and made their cells in the form which can hold the greatest possible quantity of honey with the least possible expenditure of the costly building material, viz. wax. It has been observed that it would be very difficult for a skilled workman, with the proper measure and tools, to make regular hexagonal wax cells, although Diess performs a swarming crowd of bees in a dark hive with the greatest accuracy. Whatever instinct one may assume, it seems at first quite incomprehensible how it should be able to calculate all the necessary angles and areas, or even judge whether they are correctly made. In the meantime the difficulty is not as great as it seemed at first; for all this beautiful work can be derived from a few very simple instincts of nature. as it seems at first; for all this beautiful work can be derived from a few very simple instincts of nature. as it seems at first; for all this beautiful work can be derived from a few very simple instincts of nature.
I was led to pursue this subject by Mr. W ATERHOUSE , who has shown that the form of the cells is closely related to the presence of neighboring cells, and the following view is perhaps only a modification of his theory. Let us turn to the great principle of gradation, and see whether nature reveals to us her method of working. At one end of the short[p. 253]In the series of steps we see the bumble-bee using its old coccons for taking honey, sometimes attaching short tubes of wax to them, and also making discrete and very irregularly rounded cells of wax. At the other end of the series we have the cells of the basket bee, forming a double layer: each cell is known to be a six-sided prism, the base of which is replaced by a truncated three-sided pyramid of three rhombic faces, with fixed angles. The same three diamond faces which form the pyramidal base of a cell in one layer of cells of the disk correspond to a diamond face in three adjacent cells of the opposite layer.Mexican Melipona domestica, which P. H UBERalso carefully described and illustrated. This bee is intermediate in its body structure between our honey-bee and the bumblebee, but nearer the latter, forming an almost regular waxy cell-cake, with cylindrical cells in which the young are tended, and moreover with a few large cells for receiving Honey. These latter, viewed from their free side, are nearly circular, and of nearly equal size, assembled into an irregular mass; but the most important thing to note is that they are so close together that all the circular walls, even if they continued their circles where the cells meet, must intersect or intersect one another; therefore the walls are flattened at the adjacent points. Each of these cells, taken as a whole, has 2-3 or more completely flat lateral surfaces, depending on whether it borders on 2-3 or more other cells on the side. If a cell comes into contact with three other cells, which necessarily happens very often since all are of almost the same size, the three flat surfaces unite to form a three-sided pyramid, which, according to HUBER 'S remark , apparently the three-sided pyramid[p. 254]the base of the cells of our hive bee. As in the cells of the honey-bee, so here too the three flat surfaces of a cell participate in the composition of three other adjacent cells. It is obvious that the Melipona saves wax in this manner of formation; for the walls, where several such cells adjoin one another, are not double, and only of the same thickness as the circular parts, and each flat piece of intermediate wall participates in the composition of two adjoining cells.
Pondering this case, it occurred to me that if the Melipona had made their cylindrical cells of equal size at a given equal distance from each other, and arranged symmetrically in a double stratum, the structure thus obtained would be as perfect as that of the would have become a basket bee. Accordingly I wrote to Professor MILLER at Cambridge , and this geometer considers the following statement taken from his teaching to be correct.
If a number of equal circles are described with their centers in two parallel planes, and the center of each circle is radius × √ 2 or radius × 1.41421 (or less) from the centers of the six surrounding circles in the same layer and as far removed from the centers of the adjoining circles in the other parallel stratum [28] , and if then planes of intersection are formed between the distinct circles of both strata[p. 255]- this must result in a double layer of six-sided prisms, which stand one on top of the other with three-sided pyramidal bases formed from three rhombuses, and these rhombic and the side faces of the six-sided prisms will correspond exactly at all angles, as they do on the wax disks of the bees occur according to the most careful measurements. We may, therefore, conclude with certainty that if we were able to improve a little on the present instincts of the Melipona, which are not yet very excellent, it could furnish a structure just as wonderfully perfect as the hive-bee. So let us imagine that the Melipona makes its cells completely circular and of equal size, which would not come as a surprise, as it already does to a certain extent, and many insects excavate perfectly cylindrical cells in wood, apparently revolving about a fixed point. Let us imagine further that the Melipona arranges its cells in plane layers, as it already does with its cylindrical cells. Let us also assume (and this is the greatest difficulty) that she is somehow able to judge exactly at what distance from her co-workers who are employed at the same time she must begin her circular cells; for we have already seen them measure distances sufficient to describe all their circles so as to intersect greatly, and then have seen them connect the points of intersection by perfectly flat walls. Let us finally assume, which is not subject to any difficulty, that when the six-sided prisms are formed by cutting in the same layer of adjoining circles, they can lengthen their hexagons to a sufficient extent to contain the store of honey, as the bumble-bee puts cylinders of wax on the round mouths of its old coccons. These are the not very marvelous modifications of this instinct (no more marvelous, at least, than those which guide the bird in its nest-building), by which, I believe, the hive-bee has, by way of natural selection, acquired its inimitable architectural skill. how the bumblebee still attaches wax cylinders to the round mouths of their old coccons. These are the not very marvelous modifications of this instinct (no more marvelous, at least, than those which guide the bird in its nest-building), by which, I believe, the hive-bee has, by way of natural selection, acquired its inimitable architectural skill. how the bumblebee still attaches wax cylinders to the round mouths of their old coccons. These are the not very marvelous modifications of this instinct (no more marvelous, at least, than those which guide the bird in its nest-building), by which, I believe, the hive-bee has, by way of natural selection, acquired its inimitable architectural skill.
[p. 256]
But this theory can be proven by experiments. According to Mr. T EGEMEIER ' SProcedure I separated two honeycombs and put a long thick rectangular strip of wax between them. The bees immediately began to excavate small circular pits in it, which they widened the deeper they became, until shallow basins arose, exactly circular and of the diameter of the ordinary cells. It was very appealing to me to observe that wherever several bees began to make such cavities side by side at the same time, they kept just the right distances, that in time those basins attained perfectly the aforesaid width of an ordinary cell, so that, when when they had reached one-sixth of the diameter of the circle of which they formed a part, they had to intersect one another. Once this was the case
Then, instead of a thick, rectangular piece of wax, I put a narrow strip of wax, only the thickness of the back of a knife, colored with cochineal, into the basket. The bees at once began to dig little basins close together in it from two sides, as before; but the strip of wax was so thin that the bottoms of the basins, if they had been excavated to the same depth as before, would have had to break into one another from two opposite sides. But the bees did not allow this to happen, but stopped at times with the deepening, so that the tanks got even floors as soon as they were a little deepened; and these level floors, composed of thin plates of the red-colored wax, which were not further gnawed, came as far as the eye could discern, to lie exactly along the imagined planes of intersection between the basins of the two opposite sides of the strip of wax. In places there were small beginnings, in other places larger ones[p. 257]Portions of rhombic tablets remain between the opposed basins; but the work was not gracefully executed, owing to the unnatural state of affairs. The bees must have worked in about equal proportions on both sides of the red wax streak, when they gnawed out the circular indentations from both sides, in order to be able to leave the flat bottom plates on the partition when the work was stopped.
Considering how pliable this wax is, I see no difficulty in perceiving it from either side for the bees, once they have gnawed the wax to a reasonable thinness, and then ceased their work. In ordinary honeycombs it seemed to me that the bees did not always succeed in working from both sides at exactly the same pace. For I have noticed half-completed rhombuses at the base of a cell just begun, somewhat concave on one side, where I suspected the bees had advanced a little too rapidly, and convex on the other side, where they were more sluggish in their work been. In a very excellent case of the kind I put the comb back in the basket, let the bees work on it a short time, and then took it out again, to examine the cells again. I then found the diamond-shaped panels complemented and perfectly flat from both sides. But it had been impossible, with the extreme thinness of the rhombic platelets, to effect this by further gnawing from the convex side, and I suspect that the bees in such cases from the opposite cells fed the pliable and warm wax (which after a experiments can easily be done) in the conventional middle plane and bent until it became flat.
From the experiment with the red-colored strip it is plain to see that when the bees have before them a thin wall of wax to work on, they can make their cells of proper form by keeping themselves at proper distances from each other, equal advancing steps with the concavity,[p. 258]and make the same round cavities without breaking through the partitions. Now the bees, as can be clearly seen by examining the edge of a comb that is in the process of expanding, make a rough border or wall round the comb, and gnaw their cells out of it from opposite sides, cutting the circular circumference with their deepening extend. They never make the whole triangular pyramid of the floor of a cell at once, but only the one of the three rhombic plates, which corresponds to the extreme extremity in progress, or else the two plates as the situation involves. Nor do they ever complete the upper edges of the rhombic plates until the six-sided cell-wall is begun. Some of these statements differ from those of the justly famous older HUBER but I am convinced they are correct; and if space would permit, I would show them to be so consistent with my theory.
HUBER 'S _ _Claiming that the very first cell was hollowed out in a not perfectly parallel-sided wax wall is, as far as I have seen, not quite correct: the first beginning was always a small dome of wax; but I do not want to go into these details here. We see what an important part excavation has in cellular formation; but it would be a great mistake to suppose that the bees could not properly stand upon a rough wall of wax, i. H. build along the average plane between two adjacent circles. I have several samples that prove they can do this. Even in the rough peripheral waxy margin round a growing comb, curvatures are sometimes observed, corresponding in position to the planes of the rhomboidal basal plates of future cells. But in all cases the rough waxy wall must be worked out by gnawing away considerable portions of it from both sides. The way the bees build is strange. They always make the first raw wall ten to twenty times thicker than the extremely fine septum which[p. 259]last to remain between the cells. We shall understand better how they work if we imagine masons first piling up a broad cement wall, then beginning at the bottom, taking the same step from two sides, till there is still a thin wall in the middle, hewing away and piling up the hewn away with new cement again and again on the back of the wall. We then have a thin, constantly rising wall, which is always surmounted by a thick, rough wall. As all the cells, both just begun and those already finished, are thus crowned with a strong mass of wax, the bees can cluster and frolic about on the comb without damaging the delicate hexagonal cell-walls, which, according to Professor MILLER 'S _ _Mean thickness at the edge of the comb is 1 ⁄ 353 ″, but at the plates of the base pyramid are 1 ⁄ 229 ″ thick. By this peculiar manner of construction, the comb is continually given the required strength, with the greatest possible economy of wax.
At first the difficulty of understanding the mode of construction of the cells seems to be increased by the fact that a multitude of bees work together, each, after having worked on one cell for a while, going to another, so that, as Huber remarks, a dozen or two individuals participate even at the beginning of the first cell. I have been able to confirm this fact by coating the edges of the six-sided wall of a single cell, or the extreme edge of the surrounding wall of a growing comb, with an extremely thin layer of liquid red-colored wax, and then finding each time that the bees spread this color in the most delicate way that no painter could have done more delicately with his brush, by taking atoms of the colored wax from their place and processing round into the progressive cell margins. This way of building seems to me like a competition between many bees to balance each other, all instinctively being at equal distances from each other[p. 260]face each other, and all try to describe equal circles around themselves, but then either build up or leave ungnawed the average levels between these circles. It was indeed peculiar to behold, as sometimes in difficult cases, e.g. B. two pieces of comb hitting each other at some angle, the bees tore down the same cell and made it in a different way, sometimes reverting to a form which they had previously rejected.
If bees have a place where they can stand in a posture suitable for work — e.g. B on a scrap of wood just under the middle of a comb growing downwards, so that the comb must be built over one side of the wood—thus you can lay the groundwork for a wall of a new hexagon, so that it is exactly in its proper place under protrudes from the other finished cells. It suffices that the bees be able to stand at a reasonable distance from each other and from the walls of the cells last completed, and then they can, according to the imaginary circles, erect a partition between two neighboring cells; but, as far as I have seen, they never sharpen the corners of a cell until a large part of both that cell and the adjacent cells is finished. This power of the bees, under certain conditions, to form a rough wall at the proper place between two cells just begun, is important, because it explains a fact which at first threatened with utter overthrow the preceding theory, namely, that the cells on the extreme edge of a bee- comb are sometimes exactly hexagonal; meanwhile I do not have space here to go into this subject. Then it does not seem to me to present any great difficulty that a single insect (as is the case, for example, with the queen bee) builds hexagonal cells, if it alternates on the outside and the inside of two or three cells started at the same time, always standing at the appropriate distance from the parts of the cells just started,[p. 261]partition walls listed. It is also to be understood that an insect, taking its place at the initial point of a cell, and thence turning first to one, and then to five other points at reasonable distances from each other and from the center, the direction of the intersection -Follow levels to get a single hex; but I am not aware that a case of this kind has been observed, for no advantage accrues to the insect from the construction of a solitary hexagonal cell, since it would require more building material than a cylinder.
As natural selection works only by accumulating slight deviations of structure or instinct, all of which are useful to the individual in his circumstances of life, one may reasonably ask what is the use of a long and gradual succession of variations in the structural impulse in his present perfection-leading direction of the stem-form of our honey-bees? I think the answer is not difficult. It is well known that bees are often in great distress to obtain sufficient nectar; and I have from Mr. T EGETMEIERLearning that he had ascertained by experiments that not less than 12-15 pounds of dry sugars are consumed in the secretion of every pound of wax in a hive, hence a profuse quantity of liquid honey must be collected and consumed by the bees of a hive, to obtain the wax necessary for the building of their combs. Moreover, a large number of bees must remain idle for many days during the secretion process. A large supply of honey is also necessary for the maintenance of a strong hive over the winter, and it is well known that its safety depends chiefly on its strength. Hence a saving in wax causes a great saving in honey, and is an essential condition of the prosperity of a bee family.[p. 262]and so far be independent of the quantity of honey which the bees can gather. Suppose, however, that this last is really the case, as indeed the abundance of bumble-bees in an area is often conditioned by it, and further suppose (which is not really so) that their community live through the winter and thus require a store of honey, in which case it would certainly be to our bumblebee-bees' advantage if a slight change in their instincts caused them to draw their wax-cells a little nearer together, so that their circular walls slightly cut for a dividing wall serving every two adjoining cells in common would have to save some wax. It would therefore be an increasing advantage for our bumblebees to make their cells more and more regular, closer and closer together and united more and more into a mass, like Melipona, because then a large part of the wall delimiting each cell would also serve as a delimitation for other cells and a lot of wax would be saved. For the same reason it would be advantageous for the Melipona if they drew their cylindrical cells still closer together and made them even more regular than they are now, because then, as we have seen, the circular walls would have to disappear altogether and be replaced by planar intermediate walls where then the Melipona would yield a comb as perfect as the honey-bee. But beyond this stage Natural Selection cannot perfect the building instinct, because the honey-bee's comb, as far as we can see, is absolutely perfect in terms of wax economy.
Thus, in my opinion, the most marvelous of all known instincts, that of the honey-bee, can be explained by supposing that natural selection has gradually employed a multitude of small modifications of the simpler instincts of nature; she led the bees by slow steps to draw equal circles at given distances from each other in a double layer, and to pile up and hollow out the wax along their average planes, though the bees themselves of[p. 263]are just as unaware of the definite distances of their circles from one another as of the angles of their hexagons and the lozenges on the ground. The driving cause of the process of natural breeding was economy of wax, sufficient strength of the cells, and their suitable shape and size for the larvae. The single swarm which made the best cells, and required the least honey for the secretion of wax, thrived best, and passed its newly-acquired saving instinct to later swarms, which in turn had the best chance of success in the struggle for existence .
It has been replied to the previous way of looking at the origin of instinct that the modification of bodily structure and instinct must have taken place simultaneously and in precise proportion to each other, because a modification of the one without a corresponding change in the other would have been fatal to the animals. The strength of this objection, however, seems to rest entirely on the assumption that the two changes in structure and instinct were sudden. To illustrate the case, let us return to the great tit (Parus major), of which we spoke in the last chapter. Often perched on a branch, this bird will hold yew seeds between its feet and pound on it until it gets to the core. What particular difficulty, then, could there be for natural selection in the preservation of all the minor modifications of the beak, which made it more and more adapted for hacking open the seeds, until finally it was as well constructed for this purpose as that of the nutpicker (Sitta), while at the same time hereditary habit, or lack of other food, or accidental changes in taste, made the bird more and more an exclusive grain eater? It is here assumed that by natural selection the beak was altered after, but in connection with, the slow change of habit. But now let the feet of the great tit also change and in correlation with the beak or some other which made it more and more fitted for hacking up the seeds, until at last it was as well formed for that purpose as that of the nutpicker (Sitta), while at the same time hereditary habit, or want of other food, or accidental variations in taste, came from the bird more and more become an exclusive grain eater? It is here assumed that by natural selection the beak was altered after, but in connection with, the slow change of habit. But now let the feet of the great tit also change and in correlation with the beak or some other which made it more and more fitted for hacking up the seeds, until at last it was as well formed for that purpose as that of the nutpicker (Sitta), while at the same time hereditary habit, or want of other food, or accidental variations in taste, came from the bird more and more become an exclusive grain eater? It is here assumed that by natural selection the beak was altered after, but in connection with, the slow change of habit. But now let the feet of the great tit also change and in correlation with the beak or some other or accidental changes in taste made the bird more and more of an exclusive grain eater? It is here assumed that by natural selection the beak was altered after, but in connection with, the slow change of habit. But now let the feet of the great tit also change and in correlation with the beak or some other or accidental changes in taste made the bird more and more of an exclusive grain eater? It is here assumed that by natural selection the beak was altered after, but in connection with, the slow change of habit. But now let the feet of the great tit also change and in correlation with the beak or some other[p. 264]cause they grow larger, it is very improbable that these larger feet will incite the bird more and more to climbing, until it also acquires the remarkable disposition and ability to climb like the nutpicker. In this case, a gradual change in bodily structure would lead to a change in instinct and way of life. — Let's take another case. Few instincts are stranger than that which causes the swallow of the East British Isles to make its nest entirely of thickened saliva. Some birds build their nests out of salivated mud, and one North American Swallow-type I saw cementing their nest of twigs with saliva, and even with flakes of that substance. Is it then so improbable that natural selection by means of individual swallows, which secrete more and more saliva, finally led to a species which, neglecting all other building materials, built its nest solely of condensed saliva? And so in other cases. It must be admitted that in many cases we can have no suspicion as to whether instinct or structure first began to change; — nor can we guess through what gradations many instincts must have developed when they relate to organs of the earliest beginnings of which (such as the nipple) we know nothing at all.
There is no doubt that many other instincts that are difficult to explain can be opposed to my theory of natural selection: cases in which the reason for the emergence of an instinct cannot be seen; Cases where no intermediate stages are known; Cases of instincts apparently so unimportant that it is hard to see how natural selection could have had a part in them; Cases of almost equal instincts in animals so far apart on the scale of nature that their agreement cannot be accounted for by inheritance from a common ancestral form, but must be ascribed to independent selective activities. I do not want to go into these various cases here, but[p. 265]only stop at one particular difficulty, which at first seemed to me insurmountable and fatal to my whole theory. I will speak of the sexless individuals, or sterile females, of insect colonies; for these sexless often differ greatly in structure and instinct both from the males and from the fertile females, and yet, because they are sterile, they cannot themselves transmit their peculiar constitution further by reproduction.
This subject would lend itself to a lengthy discussion; but I want to single out only one case here, the worker ants. To state how these workers became sterile is a great difficulty, but no greater than in the case of other conspicuous changes in the organization. Because it can be proven that some six-footed u. a. Insects in a state of nature sometimes become sterile; And if this has now happened with socially living species, and if it has been to the advantage of the community that a number of individuals fit for work but unfit for reproduction should be born among them every year, then no great difficulty should have arisen for natural selection, that accident to the further development of this system. But I must get over this preliminary concern. The great difficulty lies in the fact that these workers differ widely from both the male and female ants in the rest of their structure, in the shape of the thorax, in the want of wings and sometimes of eyes, and in their instincts. As to instinct alone, the wonderful difference which arises in this respect between the workers and the fertile females would have been far better in the honey-bees[29] can be proven. If a worker ant or other sexless insect were an animal in its usual state,[p. 266]thus I should have safely assumed that all its characters had been developed by natural selection, and that especially if an individual had been born with any slight useful deviation of structure, that deviation would have been transmitted to his offspring, which would then also varied and progressed with further breeding. In the worker ant, however, we have an insect differing greatly from its parents, absolutely sterile, which therefore has never inherited accidental variations in structure, nor can it be passed on to offspring. One must therefore ask how is it possible to reconcile this case with the theory of natural selection?
In the first place, we can show by innumerable instances, both among our cultivated and among natural products, that structural differences of all species have become closely correlated with certain ages, or with only one of the two sexes. We have variations so correlated not only with the one sex alone, but even with merely the brief season when the reproductive system is active, as the nuptial dress of many birds and the hooked lower jaw of the salmon. We also have slight differences in the horns of some breeds of oxen, which are associated with an artificially imperfect condition of the male sex; for the oxen of some breeds have longer horns than of others, compared with those of their bulls or cows. I therefore find no essential difficulty in a character being correlated with the sterile condition of certain members of insect communities; the difficulty lies only in understanding how such correlated variations of structure could be slowly accumulated by natural selection.
But this apparently insurmountable difficulty is greatly diminished, or, I think, entirely disappears, when we consider that selection is applicable to the family as well as to the individual, and is therefore desirable[p. 267]can lead to goals. Thus a palatable sort of vegetable is boiled, and that individual is destroyed; but the gardener sows seed from the same stock, and confidently expects to sow nearly the same variety again. Cattle breeders want the meat to be well-streaked with fat. The animal has been slaughtered, but the breeder turns back with confidence to the same family. I have such faith in the power of breeding that I do not doubt that a breed of cattle which always produces steers with extraordinarily long horns can be slowly bred by the careful use of such bulls and cows which, mated together, produce steers with the longest horns, although no ox itself is ever able to transmit this property to its offspring. So it may well have been with social insects, a slight variation in structure or instinct, connected with the sterile condition of certain members of the community, has proved beneficial to the community, in consequence of which the fertile males and females of it do better thrived and transmitted to their fertile offspring a tendency to produce sterile limbs with the same modification. And I believe this process has been repeated often enough, until this difference between the fertile and sterile females of a species grew to the marvelous height which we now perceive in many social insects. which is connected with the sterile condition of certain members of the community, has proved useful to the community, in consequence of which the fertile males and females of it thrived better, and transmitted to their fertile offspring a tendency to produce sterile members of the same modification. And I believe this process has been repeated often enough, until this difference between the fertile and sterile females of a species grew to the marvelous height which we now perceive in many social insects. which is connected with the sterile condition of certain members of the community, has proved useful to the community, in consequence of which the fertile males and females of it thrived better, and transmitted to their fertile offspring a tendency to produce sterile members of the same modification. And I believe this process has been repeated often enough, until this difference between the fertile and sterile females of a species grew to the marvelous height which we now perceive in many social insects. to bring forth sterile limbs with the same modification. And I believe this process has been repeated often enough, until this difference between the fertile and sterile females of a species grew to the marvelous height which we now perceive in many social insects. to bring forth unfruitful limbs with the same modification. And I believe this process has been repeated often enough, until this difference between the fertile and sterile females of a species grew to the marvelous height which we now perceive in many social insects.
But there is still a greater difficulty, which we have not touched on up to now, in that the asexuals of several species of ants differ not only from the fertile males and females, but also from one another, often to an unbelievable degree, and then into 2-3 castes be shared. As a rule, these castes do not merge into one another, but are completely separate, as different from one another as two kinds of a clan or two clans of a family are wont to be. Thus at Eciton there are working and fighting individuals with extraordinarily different jaws and instincts; in Cryptocerus the workers wear the[p. 268]a caste alone, a wonderful sort of shield on her head, the purpose 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 have a tremendously developed abdomen, secreting a kind of honey, which takes the place of that which our ants obtain by milking the aphids; the Mexicans obtain it from individuals of their own kind, which they keep as "cows" in the house.
Indeed, it may be thought that I am placing an undue reliance on the principle of Natural Selection, if I do not admit that such wonderful and well-established facts at once utterly annihilate my theory. In the simpler case, where asexual ants are of only one caste, which, in my opinion, may quite easily have been separated from the fertile males and females by natural selection, in that case we may confidently conclude from the analogy with ordinary variations, that every slight useful later deviation did not immediately appear in all sexless individuals of a nest at once, but only in a few, and that only as a result of long-continued breeding of fertile parents, which most sexless could produce with useful modification, the sexless finally attained all that desired character. According to this view one should sometimes find sexless individuals of the same species of insects in the same nest, which represent intermediate stages of bodily structure; and these are indeed found, considering how seldom inEurope these sexless are examined more closely, often enough. Mr. F. SMITH has shown how amazingly these vary in size and sometimes in form in the different species of English ants, and that even the extreme forms may sometimes be completely concatenated by individuals taken from the same nest. I myself[p. 269]have been able to compare complete series of steps of this kind with one another. It often happens that the larger or the smaller workers are the more numerous, and often both are equally numerous, with an intermediate gradation. Formica flava has larger and smaller workers with some of medium size; and in this species, according to Mr. S MITH ' SObserve the larger workers with simple eyes (ocelli), which, although small, are clearly visible, while the ocelli of the smaller ones appear only rudimentary. Having carefully dissected several individuals of these workers, I can affirm that the ocelli of the latter are far more rudimentary than would have been expected from their size alone, and I firmly believe, though I dare not say with certainty, that the workers of medium size also have ocelli of medium degrees of perfection. There are, therefore, two groups of sterile workers in a nest, differing not only in size, but also in the facial organs, and being united by a few limbs of intermediate quality. I could go further and say that if the smaller ones had been the more useful to the household of the community, and consequently the males and females who supply the smaller workers had always prevailed in breeding, until all the workers attained the same quality, we should have a species of ants whose sexless ones are almost like those of Myrmica. For the workers of Myrmica have not even rudimentary eyes, although their males and females have well-developed ocelli. whose sexless ones are almost like those of Myrmica. For the workers of Myrmica have not even rudimentary eyes, although their males and females have well-developed ocelli. whose sexless ones are almost like those of Myrmica. For the workers of Myrmica have not even rudimentary eyes, although their males and females have well-developed ocelli.
I want to give another example. I so confidently expected to find gradations in essential parts of the bodily structure between the different castes of the sexless in a similar way, that I gladly accepted Mr. F. SMITH 'S offer of numerous specimens of the driver ant (Anomma ) from West Africa made use of. The reader will perhaps best gauge the magnitude of the difference between their workers if I do not give him the actual measurements,[p. 270]but communicate a strictly accurate comparison. The difference is as great as if we saw a number of laborers building a house, many being only five feet four inches high, and many others as high as sixteen feet (1:3); but then we would have to assume that the larger ones had four instead of three times as large heads as the smaller ones and almost five times as large jaws. Moreover, the jaws of these workers vary wonderfully in shape, size, and the number of teeth. But the most important fact for us is, that although these workers may be distinguished into castes of different sizes, they blend imperceptibly into each other, as does the widely divergent formation of their jaws. I can speak with confidence on this last point because Mr. LUBBOCK made drawings of this jaw with the camera lucida for me, which I had separated from the workers of different sizes.
With these facts before me, I believe that natural selection, acting upon the fertile parents, is capable of producing species which regularly also produce asexual individuals, either all of considerable size and jaws of the same condition, or all small and with jaws of of very variable formation, or which finally (and this is the chief difficulty) constitute two groups of different constitutions, one of equal size and formation, and the other variable in both respects, both arising from an initial series of stages as in Anomma, but of which the two extreme forms, insofar as they are the most useful for the community, become more and more prevalent through natural breeding of the parents who produce them,until the intermediate stages disappear entirely.
Thus, in my opinion, is to explain the marvelous appearance of two severely limited castes of sterile workers in the same nest, both distant from each other and distinct from their elders. It can be assumed[p. 271]that their production has become useful to a social insect community on the same principle as the division of labor to civilized man. The ants, however, work with inherited instincts and with inherited organs and tools, and not with acquired knowledge and fabricated implements like man. But I am obliged to confess that, with all my confidence in natural selection, without knowing the facts before me, I should never have suspected that this principle could prove so highly effective. I have therefore treated this subject with somewhat greater, though still insufficient, detail to show the power of Natural Selection, and because it presents, in fact, the gravest special difficulty for my theory. The case is also very interesting, as showing that in both animals and plants, any amount of variation in structure can be effected by the accumulation of many small and apparently accidental deviations from any utility, without all the assistance of practice and habit . For no degree of practice, habit, and will in the wholly sterile members of a church can affect the formation or instincts of the fertile members, which alone produce posterity. I am amazed that no one has yet taken the instructive case of the sexless insects of the well-known teaching L that in both animals and plants any amount of variation in structure can be induced by the accumulation of many small and apparently accidental deviations of any utility, without all the assistance of practice and habit. For no degree of practice, habit, and will in the wholly sterile members of a church can affect the formation or instincts of the fertile members, which alone produce posterity. I am amazed that no one has yet taken the instructive case of the sexless insects of the well-known teaching L that in both animals and plants any amount of variation in structure can be induced by the accumulation of many small and apparently accidental deviations of any utility, without all the assistance of practice and habit. For no degree of practice, habit, and will in the wholly sterile members of a church can affect the formation or instincts of the fertile members, which alone produce posterity. I am amazed that no one has yet taken the instructive case of the sexless insects of the well-known teaching L which alone produce the offspring. I am amazed that no one has yet taken the instructive case of the sexless insects of the well-known teaching L which alone produce the offspring. I am amazed that no one has yet taken the instructive case of the sexless insects of the well-known teaching LAMARCK 'S has opposed inherited habits.
Summary. ) I have lately attempted to show in this chapter that the mental faculties of our domestic animals vary, and that these variations are hereditary. And, still more briefly, have I endeavored to show that instincts change something in the state of nature. No one will deny that instincts are of the supreme importance to every animal. I see no difficulty, therefore, why, under changed conditions of life, Natural Selection should not also have been able to accumulate to any amount small variations of instinct in a useful direction. In some[p. 272]cases, habit, use, and disuse likely played a part. I do not believe that the facts given in this section support my theory in any way; yet, to my best conviction, none of these difficulties is capable of overturning them. On the other hand, however, the facts are suitable that instincts are not always perfect and are still subject to misinterpretation - that there is no instinct for the exclusive advantage of another animal, even if every animal benefits from the instincts of others - that the natural historical dogma " Natura non facit saltum' Applicable to instincts as well as to physical development, and just as explicable from the views presented as inexplicable in any other way: all these facts lend themselves to confirming the theory of natural selection.
This theory is supported by some other phenomena concerning the instincts. Thus by the common observation that closely allied but certainly distinct species, when inhabiting distant parts of the world, and living under considerably different conditions of existence, yet often retain almost the same instincts. So e.g. B. It may be explained by the principle of heredity how it comes about that the South American thrush lines its nest with mud in much the same way as our European thrush does; — how it is that the males of the East Indian and the AfricanRhino-birds, which belong to two different sub-clades of Buceros, both possess the same peculiar instincts to wall up their nesting females in tree cavities, leaving only a small hole in the dungeon wall, through which they can feed the female, and later the female as well providing food to young; — how it comes about that the male of the American wren (Troglodytes) builds a peculiar nest for himself, much like the male of our native species: all manners which do not occur at all in other birds. Finally, it may well not be a logically correct conclusion, but it corresponds to my way of thinking[p. 273]far better, such instincts as those of the young cuckoo, which pushes its foster-brothers out of the nest—like those of the ants which make slaves—or those of the ichneumonids which lay their eggs in living caterpillars: not as peculiarly created instincts, but to be regarded only as small emanations of a general law, which is to the advantage of all organic beings, viz.: increase and modification make the strongest conquer and the weakest succumb.
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