When humans interact with their environment, incidental structures can emerge that are in some respects comparable with the emergence of kin-based structures in Australian languages. The passing of many vehicles along gravel roads produces corrugations that form parallel lines running perpendicularly to the direction of travel. Seemingly shaped by an “invisible hand”, structures such as these emerge as an unintended consequence of lots of people doing roughly the same thing. According to Rudi Keller (1994) these epiphenomena are neither completely natural nor completely artificial. An invisible hand explanation is one that causally links the emergence of macrostructures to micro-behavioural operations.
Keller’s classic example is the traffic jam that emerges out of nowhere (a motorway shockwave). Many cars are traveling down a a busy road at 100km/h when for some reason a driver needs to brake and reduce his speed to 90km/h. So as to avoid a collision the next driver reduces his/her speed to 85km/h, the next to 80km/h, the next to 75km/h, and so on. Before long the traffic grinds to a halt without the first drivers even becoming aware of the result of their braking. The emergence of a motorway shockwave can be seen in this simulation.
Both motorway shockwaves and the corrugations on gravel roads can be partially attributed to the generalised behaviour of the drivers of the vehicles. On both sorts of roads, most drivers travel at roughly equivalent speeds because two opposing preferences relating to safe driving behaviour help them decide what speed is optimal for the various conditions.
URGENCY: Preferably make haste and do not waste time. CAUTION: Preferably slow down and look out for hazards.
As a result, drivers tend to travel slow enough to be able to brake evasively, when necessary, yet fast enough to get to their destinations without excessive delays. A structural explanation for the emergence of corrugations on dirt roads relates to factors like the physical stability of the road surfaces, the number of wheel rotations, etc. On motorways, the traffic volume has a bigger impact than the stability of the road surface. Invisible hand explanations straddle the macrostructural and the micro-behavioural levels of causation. In these two cases, the same two preferences yield different emergent structures because the macro-conditions (e.g., surface stability, traffic volumes) are not equivalent.
An invisible hand explanation can be invoked for the emergence of kin-based inflections in Murrinh-Patha. On the one hand, a macro-structural explanation is provided in the gradual reanalysis of certain grammatical markers of gender, number and (non)-siblinghood (see the paper for details). On the other hand, interactional analyses reveal that the selection of these kin-based forms can be explained in micro-behavioural terms through conversational preference organization. The invisible hand explanation straddles these causal domains. Approximately equivalent preference organization across the continent has yielded similar patterns of structuration in Australian languages. Although details of these kin-based structures differ from language to language, many of the structures have converged in type.
Joe Blythe is a research fellow at the School of Language Studies, University of Melbourne, Australia and an affiliate of the Language and Cognition Department at the Max Planck Institute for Psycholinguistics, Nijmegen in the Netherlands. The research was funded by the Australian Research Council (DP110100961 and DE130100399) and the European Research Council (240853).