By Mark W. Moffett, Ph.D.
Forming groups is a basic human drive. Modern humans are all simultaneously members of many groups — there is the book club, your poker buddies, all those fellow sport team enthusiasts. Most basic of all these groups is the connection we form with our society. This is one group people have always been willing to die for. During most of human history, foreigners have been shunned or killed. Allowing an outsider to join a society is typically an arduous process, when it is permitted at all.
A fundamental attribute of any society is that it has a clearly defined membership. It is possible for a species to be social and yet not form societies: consider herds of zebra, where the animals interact socially but can readily enter and leave the group. A society is different. It is defined by the capacity of its members to distinguish one another from outsiders, and reject outsiders on that basis. For most animals, however, surprisingly few studies have been done on this key feature of social life.
In an article just published online in the journal Behavioral Ecology I describe two methods used by different organisms to identify the members of their societies. The first appears to be used by virtually every vertebrate species other than humans. In individual recognition societies, each member has to recognize as an individual every other member of its society. This takes a lot of memory, so it might be no surprise that such societies attain a modest size, with a general limit of about a hundred individuals.
The alternative are the anonymous societies, typical of social insects. Here, the members do not necessarily know their comrades individually. Actually, some ant societies are so large that many individuals never meet each other. They are nevertheless bonded by shared “markers” called identity cues. Among social insects these cues are the hydrocarbon molecules they smell on one another, which act like a national flag embedded in each member’s body surface. As long as an ant has the right scent, its nestmates will accept it as one of them. Foreign ants have a different scent and are shunned or killed.
Human societies are anonymous, too. In the history of our species we have used language and ethnic or cultural traits (flags included) in a manner similar to how ants use hydrocarbons (though of course our social cues are more complicated and varied). So while each of us has many friends, we are like the ants in that we don’t need to know each and every individual living in our nations.
Anonymity has advantages. For one thing there need be no limit to the size a society can achieve. That doesn’t mean such societies are always large: most ants have small colonies, in some cases with a maximum of a dozen individuals. However, some ant and a few termite species are the only animals other than humans to reach populations in the low millions. More remarkable still are the even smaller number of ant species with societies that expand as long as the environment permits (competing species or an inappropriate climate can stop their growth, for example). These ants are said to have supercolonies. They are strikingly like modern humans with our expanding nations of hundreds of millions.
The size of some ant and human societies gives rise to remarkable commonalities between these organisms. Even though humans are closely related to chimpanzees, our modern civilizations are in many ways more similar to certain ant colonies than to chimpanzee communities. Living in groups of at most 100, no chimpanzee has to deal with issues of public health, infrastructure, distribution of goods and services, market economies, mass transit problems, assembly lines, agriculture, warfare, and slavery. Ants have behavior addressing all these issues.
There are also of course radical differences between ant and human societies Here is the most interesting. Ants don’t know each other individually at all (other than being able to distinguish basic kinds of workers, such as soldiers or the queen); over an ant’s life, it develops no friends within its colony. The bond of each ant is totally to the society itself. As I describe in Behavioral Ecology:
Their unbreakable group identity makes ants in colonies powerful analogs of cells in bodies… Ants identify each other using chemical cues on their body surfaces, and in a healthy society, they invariably avoid or kill alien ants with different cues; cells identify each other by means of chemical cues on their surfaces, with the immune system attacking any cells with different cues.
On this basis, ants of all species can be said to form superorganisms.
Mark W. Moffett did his Ph.D. under the poet of the conservation movement, Edward O. Wilson. A research associate in the Department of Entomology at Smithsonian’s National Museum of Natural History, Dr. Moffett is most widely known for articles on ecology and animals in the National Geographic Magazine, but his own research is focused on animal sociality and on the structure of rainforest canopies. The Behavioral Ecology journal has made Dr Moffett’s article, Supercolonies of billions in an invasive ant: What is a society?, available for free for a limited time.