Science Matters

One life may comprise many lives

Boyce Rensberger

(9/2022) How is an ant colony like a human body? As far-fetched as this riddle might seem, there are so many similarities that for more than a century biologists have suggested that there are many parallels. They say we can think of an ant colony not as a family of many individual organisms but as a single "superorganism." In this concept, each ant is like a cell of our body.

In recent years this view was promoted by the late Edward O. Wilson, the Harvard biologist who was the world’s foremost authority on ants and who helped establish the specialty of sociobiology. Scientists in that field argue that the social behavior of animals—that is, how individuals behave when interacting with other individuals—is controlled by genes that have evolved through the same processes of natural selection that shaped body form. Wilson, who died in 2021, also argued that both the human body and the ant colony appear to be governed by similar rules.

In one case, the rules control an early human embryo’s clump of undifferentiated cells as it develops into a complex organism of many specialized cells. In the other case, similar rules guide the organization of a newly founded ant colony, producing a tightly knit society in which different forms of ants carry out specialized jobs as part of a single colony.

The two processes of development—embryogenesis and sociogenesis—are normally considered unrelated. But Wilson held that evolution, in dealing with similar problems, has converged on similar solutions. His ideas offer a fascinating reminder that, for all the diversity among various forms of life, there is an underlying unity in its fundamental aspects.

Wilson's ideas revived a concept that has intrigued biologists for much of a century—that colonies of social insects (ants, bees, and wasps, for example), because they are such rigorously structured organizations of specialized individuals, should be regarded as a "superorganism." A few years before he died, Wilson elaborated on these ideas in a book with Bert Holldöbler, another biologist, called The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies.

A corollary idea holds that multicelled organisms—such as animals like us—may be thought of as superorganisms made up of many one-celled creatures that have become specialized for different functions. After all, some human cells still resemble free-living microbes: there are white blood cells called macrophages that behave like amoebas, slithering about the body, eating bacteria and other bodily wastes. Sperm cells propel themselves with whiplike flagellae like those of some protozoans. Most cells in our bodies can be extracted and placed in a dish of nutrient broth, whereupon they will revert into an amoebalike shape and begin crawling about, a fully independent organism.

In making his case, Wilson noted first that social insect colonies may be surprisingly large, containing millions of individuals. Single colonies of African driver ants, for example, may contain more than 20 million workers. Within a colony, workers come in many physical forms, called castes, each suited to a different job. If the colony is considered a superorganism, the castes would be analogous to organs. There are "soldier" castes with big heads and powerful jaws that stay near the nest’s entrance to defend against invaders. Other castes leave the nest to forage for food and bring it back to share. Still others stay behind and tend the eggs, or feed the egg-laying queen, or process food so that yet others may feed larvae.

Even the position of the insect in the colony's elaborately subdivided nest may be fixed. There are, for example, ants that live most of their lives outside the nest, others that perform their jobs in the nest’s more peripheral chambers and still others that remain deep inside, never seeing the light of day. And, like circulatory and nervous systems, there are ants that travel among all the chambers, carrying food or messages. Social insects communicate with one another by releasing odors, called pheromones, a process analogous to the way our cells communicate through the release of hormones.

Among certain termites, specialties exist even within what might be called the colony's digestive system—castes that gather blades of grass and turn them over to other specialists that eat the grass, digest it partially and excrete the material onto the colony’s fungus-growing chambers. Workers of various castes that remain inside the nest eat only the excreted material and produce the final feces.

In most ant species the castes differ in form and size, some being as much as 300 times larger than their siblings in other castes. Often workers are so specialized that they lack the abilities of ordinary individual organisms. Nearly all workers, for example, have no reproductive organs, leaving the queen and a few fertile males to function as the colony’s reproductive system.

Underlying a colony’s analogies with an organism, Wilson asserted, is a developmental process that creates a new colony from a mated queen in a way remarkably like the process that produces a new organism from a fertilized ovum. All the cells of an individual organism have identical sets of genes, of course; the differences that give rise to organs arise as cells selectively shut off specific genes and activate others.

In much the same way, all the descendants of the queen are as alike genetically as the cells of any one of us humans and yet develop into ants of many different sizes, shapes, and behaviors.

The first offspring of a new queen tend to be much alike, but as she lays more eggs and enlarges the nest, the specialties appear, the result of such factors as differences in the size of the egg, the kind of food given to larvae, chemicals secreted by adult members of the colony, and the age of the individual. Some workers pass through different castes as they mature. Over time, the nest becomes more complex architecturally and the social relationships among individuals grow more interdependent. A human embryo is much the same.

Wilson's assertions about developmental rules were the result of experiments on ant colonies he kept in his laboratory, where I visited numerous times. By manipulating the colonies—removing an entire caste, for example, or changing the population ratios of one caste to another—Wilson was able to study how the colony responds.

Such experiments are like those of embryologists when they tinker with an animal embryo to learn when and how a cell becomes specialized and whether a specialized cell can revert and change into a different cell type—perhaps even go back to being a stem cell—to rebuild damaged tissue.

The rules that have emerged are complex but, in general, they reveal that embryogenesis and sociogenesis are the result of evolution arriving at the most efficient patterns of information processing.

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