Emergence in ant colonies

Go to the ant, you sluggard;
    consider its ways and be wise!
It has no commander,
    no overseer or ruler,
yet it stores its provisions in summer

and gathers its food at harvest.

    Proverbs 6:6-8

Ant colonies are amazing. It is incredible what they can achieve. I love the video below. It highlights how complex structures and functions emerge in an ant colony even though there is no individual directing the whole operation.

Ant colonies are often cited as an example of emergence, including how complexity can emerge from simple rules. Ant colonies feature in Godel, Escher, Bach by Douglas Hofstadter, Emergence: from chaos to order by John Holland, and Emergence: The Connected Lives of Ants, Brains, Cities, and Software by Steven Johnson.

Important steps towards describing and understanding a system with emergent properties include identifying how to break down the system into single components and determining how those components interact with one another.

As described in the video the colony is composed of several distinct classes (castes) of ant: soldiers, excavators, foragers, garbage collectors, and gardeners. Each ant has a very limited repertoire of methods to interact with other ants and their environment. Ants have poor hearing and sight. They communicate with a few signals involving touch, but mostly communicate by producing trails of distinct chemicals (pheromones).  Each organic molecule is identified with a specific message such as follow this trail, detection of food, presence of an enemy, or danger.

For an ant colony the components are simple and the interactions between the parts are simple. Nevertheless, complex structures such as bridges and tree houses emerge. There is no chief engineer directing the construction of these structures or a blueprint drawn up by an architect. The queen is not a dictator mandating that the colony must last for her lifetime, which covers many generations of worker ants.

Ant colonies have characteristic properties of emergent systems. The system has properties that the individual components do not. Complex structures can emerge from a system with simple components and interactions. The properties that emerge are hard to predict a priori. That is if one only knew about the properties of individual ants and how they interact, and not the properties of the colony, it would be hard to predict that they could achieve what they do.

Universality is highlighted in a nice review article, The principles of collective animal behaviour by D.J.T Sumpter. Some of the abstract is below.

I argue that the key to understanding collective behaviour lies in identifying the principles of the behavioural algorithms followed by individual animals and of how information flows between the animals. These principles, such as positive feedback, response thresholds and individual integrity, are repeatedly observed in very different animal societies. The future of collective behaviour research lies in classifying these principles, establishing the properties they produce at a group level and asking why they have evolved in so many different and distinct natural systems.