in the progressive, but not steady, improvement in function: after modifying the burrow, its acoustical performance sometimes improves and sometimes worsens. But by making certain modifications after performance worsens, and other modifications after performance improves, the cricket eventually creates a high-performance acoustical system. The only thing the cricket need carry around in its genes is the fairly simple behavioral program for burrow building and a sensory system capable of assessing the burrow's acoustical properties and correcting its structure as needed.

As physiology, there is nothing really very remarkable about this process. Feedback loops like this operate at all organizational levels within organisms to control their shapes and functions. What is remarkable about the construction of the singing burrow is that the feedback loop extends outside the cricket's body, involving a structure created by the animal and the cricket's use of energy to impose orderliness on its physical environment. The burrow, in short, is as much a part of the physiological process of communication as is the cricket's muscles, nervous system, and body.

And truly it is strange that, with such a government, the termitary should have endured through the centuries. In our own history republics that are truly democratic are in a very few years overwhelmed in defeat or submerged by tyranny; for in matters politic our multitudes affect the dog's habit of preferring unpleasant smells, and will even, with a flair that hardly ever fails, single out the most offensive of them all.

— MauRiCE MaEtERLinCk, the life of the white ant (1930)

chapter eleven

The Soul of the Superorganism

The social insects, which include the bees, wasps, ants, and termites,1 seem to attract a lot of pesky metaphor-makers. At various times, the social insects have been pressed into service as exemplars of well-ordered societies, as arguments for the necessity of monarchs, as lessons on the conflict between free will and responsibility, as linguists, as practitioners of slavery and of warfare, or, as Maeterlinck suggests, as metaphors for the failures of democracy. I could extend the list indefinitely, for the tendency to metaphor is pandemic. I might seem to be picking on philosophers, but scientists are just as prone to the disease.

In this chapter and the next, I examine one of the most powerful of the scientific metaphors that have built up around the social insects, the concept of the superorganism. I have used the word before in its adjectival form—superorganismal physiology—to describe physiological processes that extend beyond the conventionally defined boundaries of the organism. The noun has a much broader meaning: a super-organism is any association of living things that, through the coordinated actions of its members, behaves with all the attributes of an organism. Thus defined, the term has been used to describe things as varied as ecosystems, symbioses, human societies (par-

1. The bees, ants, and wasps are closely related members of the insect family Hymenoptera ("membrane wing"). The termites are only distantly related to the Hymenoptera, being members of the family Isoptera ("similar wing"), descended from the cockroaches. Estimates put the origin of termites at 75 to 150 million years ago, while the ancestors of wasps are thought to be at least 100 million years older than this.

ticularly transient and unruly associations like mobs), as well as the colonies of social insects.

In taking up the idea of the superorganism, I will be treading onto controversial ground, because it challenges strongly held notions that the living world is composed of discrete organisms. The superorganism idea has had many ups and downs in its history, for a variety of reasons. Sometimes there are just more interesting and powerful ways to think about sociality (Box 11A), and sometimes the superorganism as a model has been associated with thoughts, particularly about humans and their societies, deemed to be impure or politically distasteful. Nevertheless, no matter how assiduously the scholars of the day try to smother it, the superorganism seems, a la Mr. Micawber, to keep turning up. Indeed, the 1990s has seen a renaissance of the idea, most notably in the earth sciences, where it has reappeared in the form of the Gaia hypothesis, James Lovelock's and Lynn Margulis's remarkable conception of the Earth as a single living entity, a superorganism.

In this chapter, we will explore the idea of the superorganism in the relatively prosaic context of the social insects. In particular, I wish to explore a phenomenon known as social homeostasis. Referring to the supposed regulation of the physical environment of the nest,2 social homeostasis is the superorganismal analogue of homeostasis (or, as I shall call it from here on, organismal homeostasis). Like the regulated internal environment of an organism, the environments of many social insect nests are very stable. This stability is not evidenced by individual members of the colony; rather, it emerges only when the many individuals or

2. Some clarification of terminology is in order here, because each group of social insects has a jargon associated with it. I shall use the term colony to describe the assemblage of individual organisms that make up a familial unit. For example, a termite colony represents the descendants of a single queen, as well as the symbionts associated with them. The nest is the structure in which a colony is housed. Among honeybees, the nest is sometimes referred to as a hive. Among termites, the nest often has associated with it ancillary structures, the most spectacular being a mound.

ganize into the colony. This emergence of homeostasis in the context of the colony is what we will call social homeostasis.

My aim in this chapter is to present social homeo-stasis in the context of the "breathing" of social insect colonies, that is, the exchange of respiratory gases between an insect colony and its environment. In particular, I will focus on how structures built by social insects aid in the regulation of their nest environments.

What Homeostasis Is

In any discussion of social homeostasis, it is important at the outset to distinguish between the outcome and the process of homeostasis. The stability of some property, like an animal's body temperature or the concentration of some substance in its blood, is one obvious outcome of homeostasis. Indeed, that is the literal meaning of the word: homeo (steady)-stasis (state). Stability in and of itself, though, is not homeostasis. A fish living in the abyssal oceans will have a stable body temperature and a stable composition of salts in its blood in large part because it lives in an environment that is itself very steady. Nor is it necessarily homeosta-sis if an animal's internal environment remains steady in an unsteady environment. In contrast to your average small-bodied lizard, for example, a large monitor lizard (which can weigh in at a few dozen kilograms) has a stable body temperature throughout the day, even when faced with large daily fluctuations of environmental temperature. However, the stability of the monitor lizard's body temperature reflects more its thermal inertia than homeostasis: a large rock could be considered as "homeostatic" as a large lizard, by this logic. So simple steadiness of the internal environment—the outcome—is not sufficient evidence for ho-meostasis.

Homeostasis results, rather, from a regulatory process. To qualify as homeostasis, a system should display the signs of that process in operation—ideally, signs that are independent of the context within which it is working. That way, we are not limiting the phenom-

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