5. This is also exhibited by all ants that harbor root-aphids and root-coccids in their nests. Not only are these insects kept in confinement by the ants, but they are placed by them on the roots. In order to do this the ants remove the earth from the surfaces of the roots and construct galleries and chambers around them so that the Homoptera may have easy access to their food and even move about at will.
6. Many ants construct, often at some distance from their nests, little closed pavilions or sheds of earth, carton, or silk, as a protection for their cattle and for themselves. The singular habit may be merely a more recent development from the older and more general habit of excavating tunnels and chambers about roots and subterranean stems.
7. The solicitude of the ants not only envelops the adult aphids and coccids, but extends also to their eggs and young. Numerous observers have observed ants in the autumn collecting and storing aphid eggs in the chambers of their nests, caring for them through the winter and in the spring placing the recently hatched plant lice on the stems and roots of the plants.
In the foregoing I have discussed the ethological relations of ants to a variety of other organisms. This, however, did not include an account of some of the most interesting symbiotic relations, namely, those of the ants to other species of their own taxonomic group and to termites. This living together of colonies of different species may be properly designated as social symbiosis, to distinguish it from the simple symbiosis that obtains between individual organisms of different species and the intermediate form of symbiosis exhibited by individual organisms that live in ant or termite colonies.
The researches of the past forty years have brought to light a remarkable array of instances of social symbiosis, varying so much in intimacy and complexity that it is possible to construct a series ranging from mere simultaneous occupancy of a very narrow ethological station, or mere contiguity of domicile, to an actual fusion, involving the vital dependence or parasitism of a colony of one species on that of another. Such a series is, of course, purely conceptual and does not represent the actual course of development in nature, where, as in the animal and vegetable kingdoms in general, development has not followed a simple linear course, but has branched out repeatedly and terminated in the varied types at the present time.
It is convenient to follow the European writers, von Hagens, Forel, Wasmann, and others, in grouping all the cases of social symbiosis under two heads, the compound nests and the mixed colonies. Different species of ants or of ants and termites are said to form compound nests when their galleries are merely contiguous or actually interpenetrate and open into one another, although the colonies which inhabit them bring up their respective offspring in different apartments. In mixed colonies, on the other hand, which, in a state of nature, can be formed only by species of ants of close taxonomic affinities, the insects live together in a single nest and bring up their young in common. Although each of these categories comprises a number of dissimilar types of social symbiosis, and although it is possible, under certain circumstances, as will be shown in the sequel, to convert a compound nest into a mixed colony, the distinction is nevertheless fundamental. It must be admitted, however, that both types depend in last analysis on the dependent, adoption-seeking instincts of the queen ant and on the remarkable plasticity which enables allied species and genera to live in very close proximity to one another. By a strange paradox these peculiarities have been produced in the struggle for existence, although this struggle is severer among different species of ants than between ants and other organisms. As Forel says: "The greatest enemies of ants are other ants, just as the greatest enemies of men are other men."
3. The Taming and the Domestication of Animals[83]
Primitive man was a hunter almost before he had the intelligence to use weapons, and from the earliest times he must have learned something about the habits of the wild animals he pursued for food or for pleasure, or from which he had to escape. It was probably as a hunter that he first came to adopt young animals which he found in the woods or the plains, and made the surprising discovery that these were willing to remain under his protection and were pleasing and useful. He passed gradually from being a hunter to becoming a keeper of flocks and herds. From these early days to the present time, the human race has taken an interest in the lower animals, and yet extremely few have been really domesticated. The living world would seem to offer an almost unlimited range of creatures which might be turned to our profit and as domesticated animals minister to our comfort or convenience. And yet it seems as if there were some obstacle rooted in the nature of animals or in the powers of man, for the date of the adoption by man of the few domesticated species lies in remote, prehistoric antiquity. The surface of the earth has been explored, the physiology of breeding and feeding has been studied, our knowledge of the animal kingdom has been vastly increased, and yet there is hardly a beast bred in the farm-yard today with which the men who made stone weapons were not acquainted and which they had not tamed. Most of the domestic animals of Europe, America, and Asia came originally from Central Asia, and have spread thence in charge of their masters, the primitive hunters who captured them.
No monkeys have been domesticated. Of the carnivores only the cat and the dog are truly domesticated. Of the ungulates there are horses and asses, pigs, cattle, sheep, goats, and reindeer. Among rodents there are rabbits and guinea-pigs, and possibly some of the fancy breeds of rats and mice should be included. Among birds there are pigeons, fowls, peacocks, and guinea-fowl, and aquatic birds such as swans, geese, and ducks, whilst the only really domesticated passerine bird is the canary. Goldfish are domesticated, and the invertebrate bees and silk-moths must not be forgotten. It is not very easy to draw a line between domesticated animals and animals that are often bred in partial or complete captivity. Such antelopes as elands, fallow-deer, roe-deer, and the ostriches of ostrich farms are on the border-line of being domesticated.
It is also difficult to be quite certain as to what is meant by a tame animal. Cockroaches usually scuttle away when they are disturbed and seem to have learnt that human beings have a just grievance against them. But many people have no horror of them. A pretty girl, clean and dainty in her ways, and devoted to all kinds of animals, used to like sitting in a kitchen that was infested with these repulsive creatures, and told me that when she was alone they would run over her dress and were not in the least startled when she took them up. I have heard of a butterfly which used to come and sip sugar from the hand of a lady; and those who have kept spiders and ants declare that these intelligent creatures learn to distinguish their friends. So also fish, like the great carp in the garden of the palace of Fontainebleau, and many fishes in aquaria and private ponds, learn to come to be fed. I do not think, however, that these ought to be called tame animals. Most of the wild animals in menageries very quickly learn to distinguish one person from another, to obey the call of their keeper and to come to be fed, although certainly they would be dangerous even to the keeper if he were to enter their cages. To my mind, tameness is something more than merely coming to be fed, and, in fact, many tame animals are least tame when they are feeding. Young carnivores, for instance, which can be handled freely and are affectionate, very seldom can be touched whilst they are feeding. The real quality of tameness is that the tame animal is not merely tolerant of the presence of man, not merely has learned to associate him with food, but takes some kind of pleasure in human company and shows some kind of affection.