E.O. Wilson and Bert Hölldobler have spent much of their long careers studying ants and the boggling intricacies of their society. In the fall they published The Superorganism, a sequel of sorts to 1990’s Ants, the landmark work that won them a Pulitzer Prize. The new work is a book-length explication of the title’s conceit: A colony of insects such as ants, comprising many thousands of individuals, acts as a single organism. This may sound like a facile concept, but it is actually a precise one, and one that provides real insight into how such a society functions. But more important, the idea and the species it describes serve as the test case in the latest round of a long fight in evolutionary theory over the origins of altruism, one that dates back to Darwin.
According to Wilson and Hölldobler, the individual in a superorganismic society performs functions that, in less social species, are the responsibility of an organelle, cell, or organ, making a superorganism analogous at every level to a simple organism. So, for example, the queen is the only member of an ant colony that procreates; thus, the queen is the colony’s gonad. A hive of honeybees, too, can be thought of as a superorganism. An individual honeybee has a weak immune system, but the weakness of an individual honeybee’s immune system is compensated for by the fastidiousness of certain colony members. Those cleaners are the cells of a collective immune system, one that is located not within the body, but within the group.
In superorganismic societies, as Hölldobler and Wilson explore in great detail, there exist different castes — queen, gyne, and various worker subcastes — each of which plays a specific role determined ultimately by its genetics. The trait of cleanliness, for example, is passed to the workers by their mother, the queen, since she is the sole source of genetic material for the colony. Yet she does not clean.
Cleanliness is not the only trait distinct from queenliness — parental care and foraging are also carried by the queen but not expressed. “There are traits that are expressed in the workers that are not expressed in the queen,” says Hölldobler. “The colony’s traits are the phenotype of the queen, but it is not really the queen’s phenotype. It is the extended phenotype. The colony, even the nest structure, is part of this extended phenotype.”
It is the colony, say Hölldobler and Wilson, that natural selection evaluates — not the individual, as is usually the case — and so fitness is a measure of group performance. A fitter individual does not produce more copies of herself, and how could she, since unless she is a queen she does not reproduce? But a fitter colony, by managing its resources well, produces more females who will go on to found colonies of their own. The result of selection is not more individuals, really, but more colonies.
This phenomenon of selection at the group level is well established and universally acknowledged among those who study eusocial insects (such as ants, termites, and some bees and wasps). But it is impossible to call it “group selection” without stirring up a hornet’s nest: A theory called group selection was refuted and abandoned in the 1960s, replaced by W.D. Hamilton’s theory of kin selection and inclusive fitness that became, and remains, the standard description of what powers evolution.
E.O. Wilson subscribed to Hamilton’s theory too. But in the year or so leading up to the publication of The Superorganism, Wilson publicly reversed his thinking on group selection. In late 2007 he teamed up with unreconstructed group selectionist David Sloan Wilson to publish a manifesto-like review article titled “Rethinking the Foundations of Sociobiology,” the field that E.O. Wilson synthesized. By doing so, E.O. Wilson made a brash statement in favor of Sloan Wilson and the démodé theory he has been hashing out for the past 40 years. Now called multilevel selection — to reflect the belief that selection can operate on many levels, including the gene, the individual, the group, the species, and even the ecosystem — it’s an idea, say the Wilsons, that deserves a second look.
The reaction to E.O. Wilson’s volte-face has in some cases been vehement. Iain Couzin, a professor of animal behavior at Princeton who studies group decision making in fish, has been shocked by how provocative the debate has become.
“They’re at each other’s throats,” he says. “But I’ve admired Ed Wilson my whole career. It’s good to see him on the edge of the controversy. It can only be a good thing.”
