The ants were Wilson's first love and his deepest expertise, but they were never, in his understanding, the whole of the story. Advanced social life has arisen in the insects not once but several times over, independently, in lineages far removed from one another on the tree of life — and it was this repetition, this convergence, that Wilson found most illuminating of all. For if eusociality had appeared only among the ants, it might be dismissed as a fluke, a single improbable accident. That it arose again among the termites, and again among various bees, and again among certain wasps — each lineage crossing the same threshold by its own separate path — tells us instead that the conditions favoring it must recur in nature, that there is something about the situation of certain insects that repeatedly rewards the surrender of individual reproduction to the collective. This chapter turns from the ants to the other great social insects, and to the lesson their convergence teaches.
Wilson made this comparative method central to his science, and the reason is worth stating plainly. A single case, however thoroughly studied, cannot by itself reveal which of its features are essential to social life and which are mere accidents of one lineage's history. Only by setting the independent origins side by side — asking what the ants, the termites, the social bees, and the social wasps share despite their separate ancestries, and where they differ — can one begin to distinguish the general principles of social evolution from the particular quirks of any one group. The other social insects were, for Wilson, not a lesser subject than the ants but an indispensable comparative frame, the control cases against which the ant story could be read. He complained, in fact, that the social insects were neglected in the textbooks in favor of vertebrate examples, when many of the key concepts of social biology had originated in the study of these small creatures.
Among the social insects other than ants, the bees offer perhaps the most instructive spectacle, because they display, across their many species, a complete spectrum of social organization. Wilson stressed this repeatedly: the bees range from wholly solitary species, in which each female builds and provisions her own nest and there is no society at all, through various intermediate and communal forms, up to the highly social species with their elaborate colonies. This full gradient, preserved in the living diversity of bees, is a kind of natural laboratory for the study of how sociality arises, for it lays out something close to a sequence of steps by which the solitary life might be transformed into the social one. To study the bees is to see the evolution of society not as a single leap but as a graded ascent, each rung of which is occupied by some living species.
At the summit of bee sociality stands the honeybee, whose colony Wilson regarded as one of the most sophisticated societies on Earth. The honeybee colony is organized much as an ant colony is, around a single reproductive queen served by a force of sterile female workers, but it has evolved its own remarkable specializations, above all in the realm of communication. The celebrated waggle dance, by which a returning forager conveys to her nestmates both the direction and the distance of a food source through a stylized movement performed in the darkness of the hive, is a symbolic communication system of a sophistication unmatched among the insects and rare anywhere outside human language. Wilson treated the dance as a high-water mark of what insect communication can achieve, a signal that conveys abstract information about a place the receiver has never seen. That the honeybees should have evolved so different a solution from the chemical trails of the ants — a dance where the ants use scent — is itself a lesson in how convergent social evolution can arrive at the same functional end, the sharing of information about food, by strikingly different means.
The honeybee, so long the classic subject of behavioral study, has in recent decades become a subject of molecular study as well, and Wilson followed this development with interest. The sequencing of the honeybee genome opened the way to what he and Hölldobler called sociogenomics — the study of the genes involved in social behavior, an effort to trace the molecular underpinnings of caste, division of labor, and communication down to the level of DNA. Here the oldest questions of insect sociology met the newest tools of genetics, and Wilson, ever the champion of uniting fields, welcomed the convergence. The honeybee, whose dance had revealed the behavioral sophistication of insect society to an earlier generation, now promised to reveal its genetic foundations to a new one — the same animal serving as a model organism across a century of changing science.
Between the solitary bees and the honeybee lie the bumblebees, and Wilson valued them precisely for their in-between status. The bumblebees form colonies smaller and typically annual, founded anew each year by a lone queen, lacking the great perennial permanence of the honeybee hive — an instructive intermediate grade of sociality, neither solitary nor fully advanced. In such intermediate forms one can watch the machinery of society in a simpler state, the division of labor less rigid, the colony cycle more compressed, the queen still doing work that in the honeybee would fall entirely to workers. Comparing the bumblebee with the honeybee at one extreme and the solitary bees at the other, Wilson could trace how increasing social complexity transforms the life of a colony step by step. The bees, taken together, are the social insects' great demonstration that sociality is not all-or-nothing but a matter of degree.
The social wasps offered Wilson yet another independent origin of advanced society, and with it another angle on the general problem. Like the ants and bees, the social wasps had crossed the threshold into cooperative, brood-rearing colony life on their own separate line of descent, and Wilson prized them for the comparative leverage they provided. Their nests — the intricate constructions of paper, chewed wood fashioned into combs and envelopes — are marvels of collective building, their architecture reflecting at once the organization of the colony and its needs for defense and the rearing of brood. But it was in the matter of caste that the wasps proved most illuminating, for they revealed a route to the division of labor quite different from the fixed anatomical castes of the ants and termites.
Among many social wasps, Wilson observed, reproductive roles are settled not by irreversible morphological castes, built into the body during development, but through ongoing dominance interactions among the adult females of the colony. Which female lays the eggs and which do the labor is determined by contest and rank, a social hierarchy negotiated and continually renegotiated among individuals who are, anatomically, much alike. This means that caste in such wasps is behavioral and flexible rather than fixed: an individual can shift its role as circumstances and colony needs change, and a worker may, on the death of a dominant, ascend to reproduce herself. Wilson recognized in this flexibility a window onto an earlier, more fluid stage in the evolution of caste — a condition from which the rigid, irreversible castes of the more advanced societies might have descended. The wasps show the division of labor still in a plastic, contested state, not yet frozen into anatomy.
That plasticity comes at a price, and Wilson did not overlook it. Because reproductive roles among such wasps are settled by contest, wasp colonies are riven by an often intense competition among the potential reproductives, a reproductive conflict that exposes, more nakedly than the serene division of labor of an ant colony, the fundamental tension at the heart of all social life: the tension between cooperation for the good of the colony and the self-interest of each individual in leaving offspring of its own. In the dominance struggles of the social wasps, the cooperative and the competitive impulses stand side by side, unreconciled and visible. Wilson saw in this not a defect of wasp society but a revelation of something usually hidden — a reminder that even the most cooperative societies are built over a substratum of individual interest that is never entirely extinguished, and that the harmony of a colony is an achievement wrung from conflict, not a simple absence of it.
But of all the social insects, it was the termites that Wilson found most theoretically arresting, for they are the great exception, the one major group of social insects that arose entirely outside the order Hymenoptera to which the ants, bees, and wasps all belong. The termites evolved their sociality separately, among the ancestral relatives of the cockroaches, on a line of descent utterly distinct from that of the other social insects — and they achieved a sociality every bit as advanced. And they did so, crucially, as ordinary diploid organisms. Where the ants, bees, and wasps share the peculiar haplodiploid genetics that has so often been invoked to explain the evolution of their sterile castes, the termites have no such peculiarity: both males and females serve as sterile workers, and their society cannot rest on the special genetic relatedness that haplodiploidy produces.
This made the termites, for Wilson, a standing challenge to any tidy genetic explanation of insect society, and he confronted the difficulty with characteristic honesty. If the advanced sociality of the ants, bees, and wasps owed itself chiefly to the extra relatedness among sisters that haplodiploidy creates, then how had the termites, lacking that advantage entirely, arrived at an equally advanced sociality? The termite exception, he candidly acknowledged, shows that relatedness alone cannot be the whole story — that other forces, ecological and developmental, must be admitted into any full account of how eusociality evolves. Among these he pointed to the advantages of defending a rich and long-lasting resource — the nest in a log of wood, which is at once shelter and food — and to the role of a life spent together in a protected space. The termites, in short, kept Wilson honest, forbidding any single-factor theory and insisting that the evolution of society is a phenomenon of several causes.
For all their separate origin and different genetics, the termites converged with the ants to a degree Wilson found striking, and the convergence is itself among the strongest evidence for his comparative approach. Termites evolved elaborate caste systems — workers, soldiers, and reproductives, each produced by its own developmental pathway from similar beginnings — closely paralleling the castes of the ants, though built on wholly independent evolutionary foundations. Their soldier castes, like those of the ants, include forms with bizarre and highly modified defensive structures, division of labor carried to a morphological extreme. They build nests, the great mounds and galleries that rank among the most impressive structures made by any animal, embodying collective construction and the sophisticated regulation of the internal environment. And they occupy comparable ecological roles, turning soil and recycling dead plant matter on a massive scale. That two lineages so distantly related should have arrived independently at such similar societies is, Wilson argued, powerful evidence that social evolution follows deep and repeatable rules.
The termites depart from the Hymenopteran pattern in one further respect that Wilson thought significant: the structure of reproduction at the colony's head. Where an ant or bee or wasp colony is typically founded and headed by a queen alone, the male having died soon after mating, a termite colony is founded and led by a long-lived royal pair, a king and queen who reproduce together over many years. This enduring partnership of both sexes at the reproductive center fundamentally alters the colony's genetics and social structure, and it is one more way in which the termites, having built a society convergent with the ants in so many respects, nonetheless built it differently at the root. Wilson relished such differences, for they are the natural experiments from which the general laws of social evolution can be inferred.
The termites also underwrite their entire way of life through a partnership of another kind, one that fascinated Wilson as an instance of how deeply symbiosis runs in the living world. Termites feed on wood, but no animal can digest the cellulose of wood unaided; the termites accomplish it only through the gut-dwelling microbial symbionts they harbor, communities of protozoa and bacteria that break down the cellulose their hosts cannot. This mutualism lies at the very foundation of termite ecology and success — the termite society is, in a sense, built upon a partnership with microbes invisible within it, a superorganism resting upon a microbial community. Wilson pointed to this dependence as a reminder that even the most impressive animal societies are embedded in, and reliant upon, the larger web of life, down to the microorganisms in a termite's gut.
Taken all together — ants, termites, bees, and wasps — the social insects came to dominate the terrestrial world of invertebrates in a way Wilson never tired of documenting. They compose an outsized share of the animal biomass of the land, particularly in the tropics, and their collective activities of soil-turning, pollination, predation, and decomposition help to structure whole ecosystems. Wilson presented this ecological dominance as the ultimate measure of the success of social life: the surrender of individual reproduction, so puzzling in the abstract, had produced in practice the most ecologically powerful insects on Earth. That the same broad outcome was reached independently by the Hymenopteran social insects and by the termites only underscored the point — social organization, wherever it arose, proved a formula for ecological triumph, lifting the lineages that achieved it to dominance over their solitary relatives.
When the ants and termites meet, as they do wherever both abound, the result is often war, and Wilson — always alert to the drama of the small — recounted such clashes with relish. The predatory ants that assault termite colonies in organized raids, and the defensive countermeasures the termites deploy against them, together compose an evolutionary arms race, each side's weapons and tactics honed against the other over ages. In one memorable passage Wilson described a battle between termites and raiding ants as a clash of insect civilizations, a miniature epic playing out on the forest floor, two independently evolved social orders meeting in combat. Such encounters are more than spectacle: they are a reminder that the social insects, ants and termites alike, are dominant players in the terrestrial world, and that their interactions structure the communities around them. Between them, ants and termites shape the soil, recycle a vast tonnage of dead matter, and compose much of the animal biomass of the lands they share.
Standing back from the particulars — the dancing bees, the contending wasps, the mound-building termites — one sees the larger point Wilson meant them to serve. The independent origins of eusociality, arising again and again in unrelated lineages, are among the clearest evidence in all of biology that evolution, presented with similar problems and opportunities, tends to arrive at similar solutions. The convergence of ants and termites upon caste, nest-building, and ecological dominance, despite their vast evolutionary separation, testifies to the power of natural selection to build the same kind of order by different roads. And the full spectrum of bee sociality, from solitary to highly social, testifies that this order is approached not by a single leap but by graded steps that living species still occupy. The other social insects, in their variety and their convergence, are the comparative evidence on which Wilson's whole understanding of social evolution rests.
It is fitting, then, that they close the opening part of this book, for they complete the foundation on which everything else is built. The social insects — ants, termites, bees, and wasps together — are the pinnacle of invertebrate social life, and their study gave Wilson the concepts, the puzzles, and the comparative method that he would carry outward, in the chapters to come, to the whole animal kingdom and at last to humanity itself. The great question their convergence poses — how and why the surrender of individual reproduction to the collective should have evolved, not once but many times — is the question that would lead him to sociobiology and to the storm it raised (see Chapter 5, The Evolution of Social Behavior, and Chapter 6, Sociobiology). The small societies underfoot, in their marvelous and repeated invention of cooperation, are where Wilson learned the questions that would occupy the rest of his life, and the rest of this book.