The Social Animal

by CARYL P. HASKINS

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MANKIND today is about to be forced to a new level of social existence. We are puzzled and worried as to how we shall even begin this exciting adventure, with its corollaries of world union and the attainment of world peace. The transition to a higher social integration is broader in its scope, more fundamental in its implications, more difficult in its execution, than anything we have tackled since the emergence of the first city-state. This is not a basically new problem to the life of our earth, however. For uncounted millennia the inhabitants of this planet have been making new integrations and rising to ever more complex levels of social existence.

These societies are fascinating to watch. For a number of years, as a hobby, I have been collecting social animals in a figurative way, observing their communal habits and drawing the inevitable comparison with our own social organizations.

Some animals are obviously social. To the prairie dogs and the lemmings, the caribou and the antelopes, the wild cattle and the elephants, the wolves and the macaque monkeys, gregarious living, in families or larger associations, is a virtual necessity throughout life. Birds like the giant “orioles” of the American tropics, the starlings and the blackbirds, the sociable weaverbirds of Africa, and many of the fishing birds such as some of the herons and the gulls and gannets, the puffins and shearwaters, the ducks and swans and geese, the penguins and the albatrosses, are by habit community nesters and live in dense associations the year round.

One thinks of reptiles as solitary creatures, but crocodiles and many lizards evince a preference for companionship, and many snakes in colder climates spend the winter in densely massed balls. Frogs are eminently gregarious in their vernal song festivals, and the newts that coast slowdy along the shallows of sandy and boggy ponds are scarcely less so. The giant schools into which such ocean fish as the mackerel and the cod habitually gather are proverbial, and the close-knit flashing balls of minnows that assemble in our brooks and ponds at breeding time are also well known.

Gregariousness is even more common among the invertebrates than among the vertebrate animals. We are familiar with the masses of ladybird beetles that winter under the rocks of mountaintops, with the swarms of the great orange Monarch butterflies that gather every fall to find their precarious way south, with the occasional hordes of grain-destroying locusts like those which plagued the Mormons. The entomologist will cite other examples less well known but fully as interesting. There are, for instance, the Psocids or bark lice, humpbacked little insects that scurry over the trunks of trees, where they live in family groups or somewhat larger herds of a few dozen individuals.

There are at least five known groups of social beetles. Some are borers in the wood of living or freshly killed trees, and are likely to be found in the giant new-fallen logs of tropical forests; others prefer wood of a more pulpy nature. A parent pair of beetles excavates a gallery in the woody tissue, and at intervals along the route, the female deposits her eggs. These eggs hatch into helpless white grubs, which are tended by their elders with a degree of care which varies with the species. The more solicitous parents chew and partially predigest wood pulp for their young; while the most fastidious actually cultivate a fungus in the woody galleries, and the young browse off the soft tissues of this white, filmy vegetable.

When the larvae become mature, they remain with the parents and rear their own progeny in the same galleries, until a moderate-sized colony, consisting of young, parents, grandparents, and sometimes still older generations, has accumulated. Eventually, individual pairs leave the overcrowded apartments and wander off to found new communities.

The entomologist would speak too of the semisocial earwigs, among which the female tends eggs and young until the latter can shift for themselves. The young must escape at an early age, however, lest the solicitude toward them change suddenly to cannibalism. The student of spiders would cite the parental care of many of the hunting species — the Lycosids and their allies, among which the young are tended by the mother much as among the earwigs — and would also point to the various tropical social spiders whose huge compound webs may be twenty feet across.

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IT is but a short step from these semisocial forms to eminently social creatures — the termites, the ants, the bees, and the wasps — in which the evolution has reached a high point of development, with many curious consequences.

These are the obviously social creatures of the earth. We think of the social mode of life as restricted to them and to man. But one wonders whether the concept need end there. Why should we think of man and such animals as these as the only, or indeed necessarily as the most interesting, examples of social life on earth? If we shift our attention from the many-celled organism to the single cell as the social unit, for example, we immediately open up a whole new world of societies.

Consider, for instance, that curious group of forms, the single-celled green flagellates, which often occur as green clouds in the water of roadside pools. These organisms have long defied systematists to rank them as either plants or animals, for they have attributes of both. Like plants, they possess chlorophyll, and many of them are well able to manufacture food by photosynthesis, the typical energy-gathering process of green plants. But they are also mobile, lashing their way through their watery world by means of rapidly vibrating filaments, or flagella, and many of them actively hunt microscopic prey and ingest it, after the manner of animal protozoans.

The green flagellates propagate by cell division, like most single cells, and among the solitary types the separation of the two daughter cells is quickly and completely effected. In one series of forms, however, a mode of life which is in some measure social has been initiated.

In the flagellate genus Spondylomorum, for example, the daughter cells remain associated after division, and attempt to do their work in common. For four generations these organisms cling together, awkwardly attached by their anterior poles, until a loose bundle of sixteen cells has accumulated, all of them mobile and active, all struggling to merge their individualities into an ill-defined colonial whole.

The arrangement of the cells in the Spondylomorum colony, in which they all attempt to point in the same direction, is an awkward one from the standpoint of mobility, and it has been improved in later members of the series. In the genus Gonium, for instance, the subsocial cells remain together for only two or four generations, but they are arranged in the form of a flattened plate, embedded in a common gelatinous matrix with their mobile ends pointing outward. In the genus Stephanosphaera this plate has become a hollow ball, with each cell pointing outward from its surface.

In Pandorina the colonial cells sometimes remain together through a further generation before the community perishes, resulting in the occasional formation of thirty-two-called globes. In Eudorina the organisms remain connected for yet another generation, thus sometimes forming a sixty-four-celled community, while in Pleodorina city-states of one hundred and twenty-eight members are known.

In the genus Volvox comes the climax of this social evolution. Here the globular colonies may comprise forty thousand member cells forming a relatively enormous — though still microscopic — green ball which rolls through the water in search of sunshine and food. All the members of this community are interconnected by strands of protoplasm; so fairly rapid communication is possible between them, and they show various kinds of coördinated action. The colony as a whole has begun to develop a personality of its own.

The green flagellates form the most striking colonies of single cells, but they are by no means the only microörganisms which live communally.

Even among the bacteria, those simplest of all truly living things, this tendency to social living has made itself manifest. The great majority of bacteria form loose colonies, which can be recognized by a typical gross external appearance, but in which the individuals are neither connected with one another nor particularly modified to social existence. Among some of the higher bacteria, such as the iron-collecting genus Leptothrix and its allies, long chains of cells are frequently formed, a single cell in width, and enclosed in a common sheath which may be tough enough so that the threads attain many-cell lengths before they are broken by mechanical stresses.

Such an organism as Bacillus rotans, on the other hand, exhibits a different sort of colonial organization. Here an entire assemblage of these individually mobile creatures exhibits an over-all motion of its own, resulting from the regulated movements of thousands of coördinated colony members. Under laboratory conditions at least, the whole community of Bacillus rotans revolves slowly on its culturemedium, presenting, when it is fully developed, the appearance of some strange microscopic spiral nebula trapped by the glistening agar surface.

The climax of social living among the bacteria, however, is found in that most striking of all colonial groups, the Myxobaeteriales. A single Myxobacterium multiplies by fission, like any simple solitary unicellular form, but, as its daughters accumulate, a common gelatinous matrix is evolved by the group, in which the cells live communally as among many of the semisocial, non-mobile bacteria. Like Bacillusrotans, however, the Myxobacteriales are mobile organisms, and, as the cells accumulate, they move about in strict concert, so that the colony as a whole travels from place to place.

As the community approaches maturity, the rodlike cells collect into dense groups at various points along the margin of the colony, and these knots soon become raised above the general surface. Gradually long tubes are formed, sometimes involute, twisted, and branched in a complex manner. The heaped-up cells make their various ways to the ends of these tubes, where they accumulate as rounded fruit-like bodies at the terminals of the branchlets, until the whole structure may come to resemble some weird and gnarled Joshua tree in miniature. Exposed to the air, the cells become dormant and relatively dry, and gradually they are broken off and drift away on the winds, to germinate under favorable conditions and repeat the process. What more highly specialized form of social existence could one desire in this, the simplest class of living things?

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IT is somewhat surprising to find evidence of rather typical community existence at the level of the single cell, where one does not ordinarily look for social activities. It is tempting, then, to look for similar evidences of the social mode of existence at a still lower level — within the single cell itself. If the insect colony is an aggregation of multicellular organisms, bound together in their coördinated existences by various sorts of ties, if the Volvox colony is a community of cells similarly attached, could a single cell, by any stretch of the imagination, be thought of likewise as a community of subcellular units, and if so, what would those units be?

This path of speculation is somewhat harder to trace, for in the single cell we have already arrived at the limit of life as we understand it, so that we must extend our parallel, beyond that point, to entities which, in the ordinary sense of the term, are nonliving.

First of all we shall have to coin a working definition for the social unit. In the higher ranges of communal existence the social unit is sufficiently selfevident and recognizable; we do not need to define it. At the level of the bird flock or the ant colony or even of the primitive colony of single cells, a society is an association of coöperating members which normally function in common, but which are capable of retaining their individuality and continuing to exist for some time when they are separated from the whole. Suppose that we do not carry the definition any further than this, but apply it as it stands to the case of the single cell.

Another obstacle that must be overcome is our ignorance of the intimate details of the single cell. We do know a good deal, to be sure, about the grosser structures of more complex single-celled creatures. We know, for instance, that the higher protozoa possess a complicated “nerve net” that functions much like our own motor nervous system in controlling the movement of the various organelles¹ of locomotion. We know that such cells have a central “brain,” the motorium, through which the impulses of the “nerve” channels are coördinated.

But intracellular components of this sort are not exactly what we want. An advanced protozoan is, relatively, a very high organism, and these units which we have singled out are complex structural entities of a yet more complex whole. It is as though we were to select a man as our example of a colony of single cells, and to call the colonial unit a head or an arm, a brain or a spinal column.

We come a little closer to our goal if we think of some of the lower plant-like cells — the algae, perhaps, and the advanced pigmented bacteria — as the “community” and think of genes, the units of heredity, or chloroplasts, the unitary structures in photosynthesis, as the “members” of the “colony.” Neither genes nor chloroplasts, to be sure, are capable of carrying on an independent existence, of having any real individuality outside of the cell worlds of which they form such indispensable parts. But in some respects they are not far from that status.

Let us go a step further down the scale and consider intracellular entities of still smaller average dimensions and still less lifelike properties as the components of the cellular “community.” Consider, for example, the nature of enzymes and their role in the life processes of single cells. Enzymes are biological catalysts, the function of which is to promote and accelerate chemical reactions which might not otherwise occur to any appreciable extent.

Enzymes contribute no energy to the reactions which they promote and are not themselves used up to any appreciable extent. Like many catalysts of a non-biological nature, they are often relatively stable molecules capable, if properly protected, of existing indefinitely outside of their cell systems without losing their activity. They therefore satisfy one condition in our definition of a society: they are component members of an association, which yet can be separated from it as entities and can maintain a separate existence.

The second criterion, that the members of a society shall function coöperatively within the group, is most strikingly met by the enzymes. Evidence piles on evidence that the very life of the cell is made possible largely by the exquisitely coördinated action of the various cellular enzymes. It is through their action in timing and directing the metabolic reactions in the cell that the products of one chemical step are made ready for use in the next.

Consider, for example, the alcoholic fermentation of sugar as performed by yeasts in the ripening of wines and spirits. Yeast fermentation gives every external appearance of being a simple unitary chemical process. It gives a quantitative yield of alcohol and carbon dioxide; hence, if we know how much sugar is consumed by a particular type of yeast, we can accurately calculate how much alcohol will be produced. The process is as reliable and as unvarying as if it were being conducted in a chemical factory.

Yet when we analyze the whole situation, we find that the procedure involves a great number of complex chemical steps, all taken in strict sequence, each depending upon the products evolved in the preceding operation, all timed to a minimum of wastage by the action of the various controlling enzymes. First of all, a molecule of a six-carbon sugar unites with two molecules of phosphoric acid to give a molecule of hexosediphosphate, which then cleaves to form two molecules of the three-carbon triose phosphate. One of these molecules is reduced to glycerophosphate for use by the organism. The other is oxidized to phosphoglyceric acid, which, by an oxidation-reduction reaction, yields a molecule of pyruvic acid and one of phosphoric acid. The phosphoric acid is then available to combine with additional sugar to start the process anew. The pyruvic acid is cleft to acetaldehyde and carbon dioxide, and finally the acetaldehyde is converted to ethyl alcohol.

Could anything appearing so superficially like a unitary process in fact be further from it? Could any example be more vivid of the close coördination between enzymically controlled reactions within the framework of the single cell?

On the basis of this single example, which can be multiplied manyfold, we may tentatively accept the view that, in certain aspects, the single cell too is a society, to which certain of the concepts of societies can properly be applied. We shall later see where some of these concepts lead us.

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THIS process of trying to identify the elements of social structure at the three levels of life that we know — the single cell, the colony of cells, and the community of many-celled organisms — gives rise to many provocative ideas. Some of the most significant are evoked by the basically similar features of the course of evolution which societies have followed at every level of life. There are impressive and mystifying elements in the perfect coördination of a society, in the gradual emergence of a new individuality at the social level. One can trace the steady increase in power and scope of that social individuality and then observe the equally steady diminution and decay of the individualities of its component parts, until they are so subordinate to the whole that they can no longer exist apart from it — until what was once a society becomes an individual of a new order.

We can find no better examples of these developments than are offered by that best-known of all social groups, the wasps and bees and ants and their various related forms. Not all wasps and bees are social creatures. Indeed, almost nine tenths of all the known forms lead strictly solitary lives. So it is possible, within this single series of insects, to observe the actual emergence of the social habit. The females of these solitary species construct numbers of exquisitely fashioned individual cells under stones or under the eaves of buildings or in the cavities of old logs or even in the stems of plants, in each of which a single egg is placed.

In due time, the egg in each of the cells hatches and the larva feeds, grows, pupates, and finally emerges as a winged adult to repeat the cycle. There is nothing obviously social in this stereotyped pattern of behavior, which has apparently been repeated, generation by generation, with little variation since very ancient times. Yet it evidently contained the seeds of the social mode of life, for it was from such forms as these, apparently, that timid transitional types arose, a few of which are living today, so that we are able to study in detail every aspect of their fugitive social existences. From them, in turn, the highly socialized bees and wasps, the yellow jackets and the honeybees, were derived.

The first hint of the approaching social condition, apparently, was an attempt by the mother insect to consolidate her work; to scatter her brood cells less widely over the country and so to conserve energy in building and provisioning. Among the more advanced solitary wasps and bees, the female may use a single cavity in which all the food packets are placed end to end, and so save the labor of cell-building altogether.

Among some species of the rare solitary bee genus Allodape the founding female begins by finding or excavating a long tubular gallery in the stem of a suitable plant. A packet of honey and pollen is assembled and crowded to the bottom of the burrow and an egg is laid on it, but no envelope is constructed about it. A second packet is built on top of the first and another egg deposited, and there follow a third and a fourth packet, until the tube is filled. The mother insect then deserts the family. Presently the eggs hatch and the larvae develop together, to pupate and emerge as adults at about the same time. They may live together in a group for a little while, but they have no real mutual interest and soon disperse. This is the first step forward.

The second step toward social existence involves two more or less parallel developments, one of which may, however, be a consequence of the other. The life span of the mother becomes prolonged until she is able to survive the maturity and emergence of her offspring. At the same time, she ceases to supply each egg with provisions. Instead she deposits all the eggs together in the cavity without any stored food, but she retains a continuing interest in them and periodically supplies them with nourishment.

These young are therefore in intimate contact with each other and with their mother throughout development, and after they have matured they remain together with her for a time as a sort of pseudocommunity on the social level of a covey of quail.

But it is not long before the group splits up and each young female member sets about founding a new family of her own. No great degree of continuity has been achieved by the society; no great degree of independence has yet been sacrificed by its members.

The next step is an extraordinarily important one. It is well illustrated by the common bumblebee. Here the solitary young queen establishes her family in the spring in essentially the same manner as the female of Allodape. She finds or excavates a burrow in the ground, constructs a cell (in this case of wax and pollen paste), deposits the eggs therein, and feeds the young, at first by the ancient method of mass provisioning practiced by Allodape, later by the more modern one of progressive feeding of the growing larvae. These young develop together, constantly presided over by the mother, and emerge together, as in more primitive forms.

But here a striking social advance becomes immediately evident, for the progeny at maturity prove not to be perfect males and females, but are females only, and stunted and imperfect females at that, some of them being no larger than houseflies. Unlike the young of Allodape, or even of more nearly social forms, they are not physically capable of founding new communities, and, what is even more important, their instinct pattern is defective in the same respect. Maternal instincts are highly developed, reproductive ones are almost wanting; these stunted daughters therefore remain tenaciously at home, attending to the rearing of subsequent batches of eggs deposited by the mother.

The founding female now gives little further attention to foraging or to the rearing of young, these duties being taken over entirely by the new workers. As the summer wears on, successive groups of workers appear, becoming larger in stature as the size of the colony increases, until finally, in the fall, true queens and males appear and the cycle which in the Allodape colony requires but one brood is at last complete. A society has been stabilized and has acquired a certain individuality. Some of the autonomy of its component members has been sacrificed, however, to the end that the newly integrated superorganism shall remain intact and shall survive.

Survival is a precarious business in such early transitional forms as these. Bumblebees, being fortunate in inhabiting the colder parts of the earth, where competition from rivals is not too intense, are reasonably common. A number of similar transitional social types are known among the wasps and bees of the tropics, however, which are among the rarest of insects, far rarer either than the solitary ancestors from which they came or the more highly socialized forms which have followed them.

The next steps in the evolution of the Hymenopteran society are familiar to us all. The colonies become more populous, as in the yellow jacket; they become more highly stabilized, as in the honeybee. The workers become sharply differentiated and more highly coördinated in the duties which they perform, and grow more and more dependent upon the colony for their continued existence. Less and less are we dealing with a colony in the definition which we gave it. More and more are we dealing with a new kind of individual.

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FURTHER stages in the story are better represented among the ants. The ants appear to be far older in evolution as social insects than are the bees or wasps. There are no living solitary ants, and the most primitive social forms of which we know, the Ponerines, are already far beyond the stage of Allodape. They form stable communities, with distinctly, though not strikingly, differentiated queens and workers. The colonies are still small in terms of the numbers of their members, however, still loose in internal construction, still poorly coördinated. There is only a primitive differentiation of function, and none of form, among the workers.

The whole process of social evolution among the ants is one of overcoming these defects, until the colonies comprise many thousands of workers, as among the leaf-cutting Attas of the American tropics or the Driver ants of the Old and New Worlds, or the huge communities of mound-building Formicas of Pennsylvania and Illinois. There has been an increase of structural differentiation between the queen and the worker, with a progressive reduction of the independence of the worker, until in the genus Carebara, a thief-ant of Africa, the queen may be ten thousand times the size of her largest worker progeny and cannot even feed her young without serious danger of crushing them.

There has been differentiation first of function and then of form among the workers until among many of the fungus-growing ants there may be many kinds of soldiers and workers within a single colony, showing among them the richest variety of specialization and adaptability. There has been a perfection of communication and coördination until, as with the slavemaking genus Polyergus, whole armies can act in concert in the attainment of a common objective.

There has been sacrifice of the individuality of the single ant to that of the community until independent existence is made almost impossible by defective instinctive endowment and even from the standpoint of physical development solitary life would no longer be easy. Coördination, regulation, subordination, and discipline of the colony members, resulting in the superior integration of the community — these have been the unmistakable trend.

The social insects probably mark the high point of this kind of development among communities of the many-celled creatures. Yet the ant colony as an individual is still a very loosely integrated structure. Interdependent as its members may be in action, any one of them can be removed from the community, be kept apart for a period, and be subsequently returned, without damage to the part or the whole.

Perhaps the course of evolution among higher multicellular organisms is still too recent to have permitted further development than this along the social road. Perhaps the fact that there is no actual permanent physical connection among the members of these colonies has inhibited their further social specialization. In any case, social evolution has been carried spectacularly further among another class of invertebrate creatures — one that is far older in the evolutionary scale, though far more primitive in structure, than the insects, where it has been possible for the members of the society to remain physically connected.

The jellyfishes are creatures which one does not ordinarily consider as social or as likely to embark on social development. Yet in one group of them, the Siphonophora, the social “superorganism” has attained a higher individuality and its component members have sunk to a lower level of independence than in any other class of many-celled creatures.

The social habit is not in fact uncommon among the allies of the jellyfishes. The polyps of corals and of the purple sea-fans, for example, form immensely populous communities; but since they remain permanently stationary, there is little differentiation among the members of a colony. The social habit has been carried over, however, into some of the mobile forms of medusae, with the most striking results, and an evolutionary series can be traced here to typify the trends involved.

The marine Siphonophoran genus Halistemma includes organisms which associate into rather diffuse colonies in which all the members are nevertheless physically interconnected. Each colony takes the form of a long pendant string to which are attached various structures, each structure actually representing a modified member of the colony. At the top of the colony is a small float, dependent from which is the slender axial fiber. A short distance below the float there are several swimming-bells, attached to the fiber by strands. These swimming-bell members of the colony possess no mouths and must be nourished by other individuals of the community, but they are highly efficient swimmers and their function is to keep the colony afloat and to move it about.

Groups of specialized polyp-like individuals are attached farther down the fiber. There are hunting polyps, equipped with mouths and single long tentacles, which capture prey, digest it, and distribute the products to the other colonial members through their connecting stems. There are curiously modified individuals which function as special protective structures, and others which have no mouths but are furnished with long tentacles to act as defensive stinging equipment or as fishing lines to capture and paralyze prey, and finally there are mouthless, tentacleless reproductive forms, the social function of which is to produce new colonies.

In the related genus Physophora the bewilderingly diffuse structure of the Halistemma colony has become compact and integrated. There is still a float with a fiber pendant from it, still equipped with specialized swimming-bells. But below the bells the fiber is shortened. The various groups of bizarre colony members have been assembled in a compact knot and the protective individuals have been grouped as a defensive ring about them. In the colonies of Stephalia, the next stage in this social evolution, the upper float has been greatly enlarged and strengthened and the swimming-bells have been grouped in an orderly circle just below it. Immediately underneath this swimming equipment the rest of the colonial members lie almost fused together in a compact mass. One can hardly fail to be reminded, in all this compacting of colonial structure, of the initial move of Allodape on the social road, of the early trend among the females of the first semisocial wasps and bees, to gather together and to compact their brood cells.

This evolution culminates in that widely known and spectacular inhabitant of tropical waters, the gorgeous Portuguese Man-of-War. In this colony the individuality of the community as a whole has been so overwhelmingly developed at the expense of its members that it is tempting to consider the “creature” the single organism which it almost is. The float, which is crested and can be deflated, allowing the colony to sink “at will” as it were, has been greatly enlarged and has usurped the entire swimming function for the community. Accordingly, the swimming-bell members of the colony have been suppressed and have disappeared.

Underneath the float is a group of feeding individuals possessing mouths but without tentacles. Associated with them, and assisting them in the capture of prey as well as in defending the colony, are several hydranths bearing poisonous fishing lines, including the stupendously long one that is so conspicuous and sometimes so startling to human bathers. Here also are the reproductive members, protectively situated near the heart of the colony, from which new individuals, and thence new communities, will arise.

Social evolution has come to a nearly full cycle. Differentiation of colony members, exquisite internal coördination, the genesis of a new, dominant, overweening composite “personality” through which the once well-marked autonomy of the colony members has been hopelessly suppressed, have at last made the colony so much like the individual from which it originally sprang that it is scarcely structurally distinguishable.

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SO MUCH for the true society as we ordinarily understand it. Let us return now to the society of single cells, to the evolution of the green flagellates already discussed. The sixteen-celled colony of Spondylomorum, its little packet of struggling members attached by their anterior poles, all striving more or less unsuccessfully to merge their individualities into that of a colonial whole, is as diffuse and poorly adapted a structure as a colony of timid, half-social Stenogastrine wasps huddling together on their frail, twisted little combs of wood fiber in the shades of Philippine jungles. There is no differentiation of individuals in form or function, and only poor coördination between them.

In the more socially advanced genus Gonium, however, protoplasmic strands have been detected connecting the colonial components. The relationships between the cells is in a sense analogous to that of the members of the jellyfish colonies, although the differentiation between the single cells is still far inferior to that among even the most primitive social medusae.

In the sixty-four-celled colonies of Eudorina, physical specialization among the members of the colony, roughly comparable in degree to that among the workers of an ant colony, has appeared. Certain cells have become specialized as the anterior pole of the structure, which now always travels wdth these cells in the lead. They have the largest eyespots and probably the highest rate of metabolism, and the size of the eyespots in the cells behind them gradually diminishes until eyes may be wholly lacking in the lowest tiers of cells.

In Pleodorina a further permanent specialization of function and form has taken place among the colonial members, with a consequent heightening of the individuality of the community at the expense of the single cell. Irregularly scattered through the colony, but for the most part in the posterior portion, occur certain large, well-provisioned cells, which may sometimes exceed the normal ones in number. These are specialized reproductive cells, and they and they only have the power of forming new communities. They are the young queens of the bee or the wasp or the ant colony.

In Volvox all these trends reach their climax in this series. The female reproductive cells are still further differentiated from their fellows. Specialization of the non-reproductive cells has been carried yet further, with greater activity and better developed sense organs in the leading members of the group, and a greater tendency to phlegmatism, to the storage of reserve food, in the trailing ones. All the cells are interconnected by conspicuous strands of protoplasm, all the forty thousand pairs of waving flagella are coördinated in their motion. The colony has nearly become an organism.

This is the end of the evolution in the Volvox series, so far as we can detect it today. But it appears to be merely the beginning of the development of cellular colonies in nature. Recent findings have indicated that there may be a rather close phylogenetic connection between creatures of the type of Volvox and that next higher, though aberrant, type of cell colony, the sponges. The channel may have led on into the whole kingdom of creatures which we call multicellular animals, to culminate at last in the vertebrates. There specialization of the cellular components has become so finely developed, there the individuality of the colony has been so exaggerated at the expense of its once independent parts, that we no longer think of these colony-animals — these flamingos or these elephants or these men — as cellular communities at all. Once again, specialization at the level of the colony member, coördination and dominance at the level of the whole.

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CAN we discern traces of these same trends of social evolution at the level of the “society” that is the single cell? Here they will be much harder to find, for of all “social” developments on earth, that of the single cell is infinitely the oldest in evolution, its early stages impenetrably buried in antiquity. Nevertheless, we may be able to discover some suggestive evidence of this same progressive internal specialization and coördination of intracellular units with evolution. Let us return to the matter of cellular enzymes.

There is much collateral evidence to indicate that the simple anaerobic bacteria, such as Clostridium tetani, causative agent of lockjaw, or Clostridium perfringens, a vector of gas gangrene, may be close to the archetype of all living microörganisms. It seems not at all impossible that they may have come down from a namelessly ancient past when the amount of free oxygen in the air was minute, when breathing as we understand it was an undiscovered art among the living cells of the day, when only the bound oxygen of water and possibly of other suitable oxides was available for respiration. The yeasts, on the other hand, appear to be relatively advanced organisms, recent in evolution in contrast to the anaerobes. It may be illuminating to compare the processes of fermentation as carried forward by these two great groups of single cells.

We have seen that the fermentation processes of the yeasts behave as if a single unitary chemical operation were involved, though in fact a large number of complex changes take place, each one of which is dependent upon its predecessors; and the whole series is so beautifully timed, the whole mosaic so exquisitely fitted together, that the coördination is remarkably perfect. The anaerobic bacteria, like the yeasts, ferment carbohydrates for a living, these sugar-like compounds forming their chief source of energy.

But, lacking both the variety and the coördination of enzymes that the yeasts possess, the anaerobes do not produce alcohol as their uniform end-product. Instead, they turn out a weird variety of metabolic products, many of which would be reckoned by a yeast cell as fertile sources of further chemical energy. Their metabolism, in fact, is both wasteful and chaotic. The Clostridiums, in fermenting a grammolecular weight of a six-carbon sugar, may produce as end-products free hydrogen, butyric acid, acetic acid, acetone, carbon dioxide, and possibly other compounds, and capture withal less than twenty calories of heat energy in the process.

A yeast cell, supplied with a gram-molecular weight of the same type of sugar, yields only ethyl alcohol and carbon dioxide, as we have seen, despite the fact that many of its intermediate products are identical with those of the Clostridiums, and captures nearly twice the energy. The anaerobes, in their prodigal wastefulness of earth’s energy sources, in the diffuseness and paucity of their “colonial” structure in terms of enzymes, in their variability and their inefficiency, offer a contrast with the yeasts that may not be fundamentally different from the contrast between the loose, ill-defined community of the bee Allodape and the industrious, close-knit hives of the commercial honeybee.

8

ALL of this collection and comparison of societies leads to some fascinating considerations, rooted in their basic similarity and in their equally significant and far-ranging differences. On the first score, there appear to be two similarities which are so fundamental as to demand an explanation — an explanation which in the present state of our knowledge of the universe it hardly seems possible to give. Every “society” that we can name, at any level of life, shows in its evolution, and particularly at its inception, a well-marked trend to proceed from a simpler to a more complex state.

The enzymes of the yeasts are more varied and more chemically complex than those of Clostridium. The cells of the Volvox colony are more numerous and more varied in their interrelationships than the sixteen units of Spondylomorum. And the Spondylomorum colony is in turn a far more complicated being than the single-celled flagellates from which it apparently arose in evolution. Even the most primitive wasp colony is a much more complex association than the single solitary wasp with her brood cells. And think of the advance in complexity from a colony of Ponerine ants, with its dozen or two component members, to the great armies of the tropical Driver ants, each of which may contain hundreds of thousands of members!

Purely on the basis of Darwinian natural selection, on the theory of “survival of the fittest,” it is not easy to understand why this unmistakable trend from the simple to the complex should be universal in the evolution of earthly societies. Over and over again we have vivid evidence that the advance from a solitary to a social existence cannot, in its early stages, have been wholly beneficial to the species in the sense that its survival value was increased relative to its competitors. The awkward, struggling colony of Spondylomorum has certainly sacrificed a good deal relative to its simple flagellate ancestors. Its agility is considerably interfered with, for the “individuality” of the colony is as low as that of an American colonial town meeting.

The ratio of its absorptive surface to its volume, that ratio which must not fall below an irreducible minimum if the cell is to survive, is reduced over that of the free-living flagellates from which it presumably arose. Its opportunities for distribution over the earth are somewhat poorer than those of the lighter, more simply constructed solitaryflagellate. It appears to be an altogether less efficient creature than its ancestors. Perhaps it is significant that only one species of Spondylomorum is known, and that it is a rare organism compared with the common solitary green forms from which we must believe that it has been derived. Every evidence seems to indicate that the first transition from the solitary to the colonial mode of life was not an expedient move.

We can trace the same picture at the next higher level of social life. The semisocial Halictid bees, the half-colonial Stenogastrine wasps, living timidly in their tiny, subintegrated communities, would seem to have sacrificed much in mobility, in distribution, in foraging ability, over earlier solitary types. They are today rare and obscure curiosities of the entomologist and the comparative sociologist. Yet the fully solitary bees and the solitary wasps from which they came are so common the world over that they include somewhat more than 80 per cent of the known species of these insects. The diffuse floating network of the Siphonophoran colony Halistemma can hardly be better off in the competition of the ocean than the compact solitary jellyfish type from which it must have been derived. Again it is hard to see that it has ever been expedient, in a Darwinian sense, for an organism to take up the social mode of existence.

The move, to be sure, was often enough vindicated somewhere later in evolution. A Spondylomorum colony may not be an efficient operating unit compared to a single cell, but the colony of cells that is a man may claim to be reasonably efficient. A colony of primitive bees is a weak and inefficient affair, and bees of this sort are comparatively rare, but the number of individual honeybees in the world may well exceed that of any solitary species, or even those of many solitary species combined, and the distribution of the honeybee is world-wide.

This vindication, this survival of the society which began in evolution at a disadvantage in an unfriendly world, has been achieved through the increase of the individuality of the colonial whole relative to that of its component parts. The solitary flagellate cell was a well-coördinated, smoothly functioning individual. The primitive cell-colonies are the very reverse of this. The individualities of their members are still well preserved. The individuality of the newly emergent social unit is perilously low.

But in Volvox this condition has already begun to change. The actions of the component cells are no longer independent; their interrelationships have been specialized and regulated. The individuality of the cell is distinctly lower than that of a cell of Spondylomorum. The individuality of the colonial unit is decidedly higher. Then think how much further this trend has proceeded in the cell colony that is a man, where very few individual cells of the body are capable of independent existence, where the regulation of cells to colonial life has proceeded to an extreme, where the individuality of the colony is at a peak and that of the component cell at a minimum.

At the next level of social life, the degree of individuality that characterizes a colony of honeybees, Maeterlinck’s “Spirit of the Hive,” is certainly higher than that of a community of the primitive Halictid bee, of the primitive Stenogastrine wasp, of the primitive Ponerine ant. How much more of an individual is the Portuguese Man-of-War, how much more like a mere glorified edition of a solitary jellyfish, than is the diffuse Halistemma colony. If other evidence were not convincing, how much more logical it would be to assume that the Man-of-War evolved directly from the primitive solitary form, without ever having gone through the precarious intermediate stage of primitive social existence.

9

IT IS clear that the ordinary forces of natural selection in evolution as we usually understand them, the common picture of “ survival of the fittest" in nature, demand the production of a streamlined, highly coördinated individual and condemn the loose, poorly integrated colony that any primitive society must necessarily be. At every level of existence, life has responded to this demand. And for the most part the abundant life-forms of today are so nearly individuals that, with the exception of the most recently evolved types, we are hard put to it to call them communities at all. Possibly that is why the “missing links” of evolution connecting solitary with social creatures are so often rare or extinct.

But if natural selection is so inimical to poorly coördinated aggregates at any level, why was social existence ever initiated? What tempted the first social bees and wasps and ants, the first social jellyfish and men, to live under these disadvantageous conditions? What tempted the early colonial flagellates to undertake that mode of life, so inconvenient by comparison with the existences of their solitary ancestors? Why is not the only form of life on earth today the single cell? What, for that matter, tempted the first groups of enzymes to associate in the working units that may have been the first simple cells — what forces led to the initiation of life at all?

These are profound questions, which reflect the constant trend from simplicity to complexity that is so evident throughout the evolution of our solar system. If we answer them, we have perhaps also answered the question as to why there is a complex organic chemistry on earth, while in the sun, from which the earth arose, the presence of only such simple chemical compounds as methene, cyanogen, and the oxides of certain metals has been detected. Of course, the riddles cannot be solved at the present stage of our knowledge or of our philosophy. It is important to notice, however, that this trend from the simple to the complex, which is so vividly demonstrated in the development of all earthly societies, may be far older and deeper than the phenomenon of life.

Natural selection, on the other hand, with its encouragement of the opposite trend, favoring the simple unitary individual over the complex, manysided aggregate, surely opposes this basic trend. The yeast cell, with its series of fermentation processes so well coördinated that they appear to be a single operating unit, has apparently been evolved from such relatively ill-coördinated organisms as are today generally represented by Clostridium. The ant, so well-knit as an insect that we think of it as an individual instead of as a colony of cells, appears with little doubt to have sprung ultimately from crude cellular colonies vaguely like those of Spondylomorum. The colony of Army ants, so closely coördinated that it can almost be thought of as an individual itself, is a product of early associations that were no more than indifferent collections of individuals.

So we are perhaps witnessing, among the societies of the earth, the cross-working of two sets of forces. The first has ever promoted the formation of complex aggregates from simpler components. It gives every evidence of being far deeper and wider, far older, than mere earthly life, though earthly life is deeply subject to it. The second is natural selection in the Darwinian sense, and it appears to be peculiar to life, and is perhaps no more ancient in its operation on this planet than the appearance of life.

No sooner has a new and more complex aggregate of living elements appeared on earth in response to the first trend than it has been subjected to the demands of the second. And so, over the millennia, the individuality of its component parts is suppressed, the units comprising it are condensed into more and more compact entities, the whole is smoothed and finished. Finally it attains a point of equilibrium in the evolution of individuality. The ancient trend to complexity is reasserted, an aggregate of a new order is formed, the old, old cycle is repeated once more, and a new level of life appears.

These are a few of the speculations which must occur to a collector of social animals. And immediately he is asked, as he perpetually asks himself, the inevitable question, the most fascinating of all: “What is the application of all these things to man and his society?” But that is a broader and a more vexing query. For the society of man, though it represents but one microcosmic example in the grand sweep of all earthly social evolution, is nevertheless a highly atypical one. Its correct placement in the scale, of which it is a part wall require, now and in the future, the most patient analysis of detail, as well as the most comprehensive knowledge of the broader evolutionary picture.