Mind, Body, World- Foundations of Cognitive Science, 2013a

next. Theraulaz and Bonabeau (1999) created a nest building simulation that only
used these two rules, and demonstrated that it created simulated nests that were
very similar in structure to real wasp nests.
In addition to adding cells laterally to the nest, wasps must also lengthen existing
walls to accommodate the growth of larvae that live inside the cells. Karsai
(1999) proposed another environmentally controlled model of this aspect of nest
building. His theory is that wasps perceive the relative difference between the longest
and the shortest wall of a cell. If this difference was below a threshold value, then
the cell was untouched. However, if this difference exceeded a certain threshold,
then this would cause a wasp to lengthen the shortest wall. Karsai used a computer
simulation to demonstrate that this simple model provided an accurate account of
the three-dimensional growth of a wasp nest over time.
The externalization of control illustrated in theories of wasp nest construction
is called stigmergy (Grasse, 1959). The term comes from the Greek stigma, meaning
“sting,” and ergon, meaning “work,” capturing the notion that the environment
is a stimulus that causes particular work, or behaviour, to occur. It was first used
in theories of termite mound construction proposed by French zoologist Pierre-
Paul Grassé (Theraulaz & Bonabeau, 1999). Grassé demonstrated that the termites
themselves do not coordinate or regulate their building behaviour, but that this is
instead controlled by the mound structure itself.
Stigmergy is appealing because it can explain how very simple agents create
extremely complex products, particularly in the case where the final product,
such as a termite mound, is extended in space and time far beyond the life
expectancy of the organisms that create it. As well, it accounts for the building of
large, sophisticated nests without the need for a complete blueprint and without
the need for direct communication amongst colony members (Bonabeau et al.,
1998; Downing & Jeanne, 1988; Grasse, 1959; Karsai, 1999; Karsai & Penzes, 1998;
Karsai & Wenzel, 2000; Theraulaz & Bonabeau, 1995).
Stigmergy places an emphasis on the importance of the environment that is
typically absent in the classical sandwich that characterizes theories in both classical
and connectionist cognitive science. However, early classical theories were
sympathetic to the role of stigmergy (Simon, 1969). In Simon’s famous parable of
the ant, observers recorded the path travelled by an ant along a beach. How might
we account for the complicated twists and turns of the ant’s route? Cognitive scientists
tend to explain complex behaviours by invoking complicated representational
mechanisms (Braitenberg, 1984). In contrast, Simon (1969) noted that the path
might result from simple internal processes reacting to complex external forces—
the various obstacles along the natural terrain of the beach: “Viewed as a geometric
figure, the ant’s path is irregular, complex, hard to describe. But its complexity is
really a complexity in the surface of the beach, not a complexity in the ant” (p. 24).
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