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

Critically, though, Evans’ programs are also controlled by releasing stimuli that
are external to the wasp. In particular, one behaviour in the sequence is presumed
to produce an environmental signal that serves to initiate the next behaviour in
the sequence. For instance, in Evans’ (1966) model of the construction of a burrow
by a solitary digger wasp, the digging behaviour of a wasp produces loosened soil,
which serves as a signal for the wasp to initiate scraping behaviour. This behaviour
in turn causes the burrow to be clogged, which serves as a signal for clearing
behaviour. Having a sequence of behaviours under the control of both internal
drives and external releasers provides a balance between rigidity and flexibility; the
internal drives serve to provide a general behavioural goal, while variations in external
releasers can produce variations in behaviours: e.g., resulting in an atypical nest
structure when nest damage elicits a varied behavioural sequence. “Each element
in the ‘reaction chain’ is dependent upon that preceding it as well as upon certain
factors in the environment (often gestalts), and each act is capable a certain latitude
of execution” (p. 144).
If an individual’s behaviour is a program whose actions are under some environmental
control (Evans, 1966; Evans & West-Eberhard, 1970), then it is a small
step to imagine how the actions of one member of a colony can affect the later
actions of other members, even in the extreme case where there is absolutely no
direct communication amongst colony members; an individual in the colony simply
changes the environment in such a way that new behaviours are triggered by other
colony members.
This kind of theorizing is prominent in modern accounts of nest construction
by social paper wasps (Theraulaz & Bonabeau, 1999). A nest for such wasps consists
of a lattice of cells, where each cell is essentially a comb created from a hexagonal
arrangement of walls. When a large nest is under construction, where will new cells
be added?
Theraulaz and Bonabeau (1999) answered this question by assuming that the
addition of new cells was under environmental control. They hypothesized that an
individual wasp’s decision about where to build a new cell wall was driven by its perception
of existing walls. Their theory consisted of two simple rules. First, if there
is a location on the nest in which three walls of a cell already existed, then this was
proposed as a stimulus to cause a wasp to add another wall here with high probability.
Second, if only two walls already existed as part of a cell, this was also a stimulus
to add a wall, but this stimulus produced this action with a much lower probability.
The crucial characteristic of this approach is that behaviour is controlled, and
the activities of the members of a colony are coordinated, by a dynamic environment.
That is, when an individual is triggered to add a cell wall to the nest, then the
nest structure changes. Such changes in nest appearance in turn affect the behaviour
of other wasps, affecting choices about the locations where walls will be added
214 Chapter 5