Triggers, Signals and Intentionality

I was recently recommended to read Ruth Millikan's work on biological intentionality. Intentionality is widely thought to be the result of anticipatory capacities of one sort or another, but quite how these capacities manifest themselves on a neurological level is a fiercely debated subject upon which Millikan takes a radical but I think entirely mistaken line. Millikan takes the view, not only that brain states are representational, but that they are essentially semantic: ‘Biosemantic.’

In the next few paragraphs I aim to show why biosemantics fails to achieve its goal of naturalising representational content, and I aim to do this by way of a discussion of the evolutionary emergence of the most basic form of signalling commonly observed in nature (i.e. rabbits thumping the ground, the tail splashing of beavers and numerous other rudimentary alarm signals).

Organisms need to be sensitive to changes in their environment and to be differentially responsive to available stimuli, i.e. capable of adjusting their  responsiveness according to prevailing circumstances. If a certain advantageous or disadvantageous circumstance is commonly preceded by other regularly occurring stimuli, then it is of significant advantage for organisms to be capable of responding effectively to these antecedent environmental triggers.

Environmental triggers, of whatever kind, should never be confused with signals. The scent that leads an organism to a source of food is not a literal signal propagated by the food, nonetheless it is a potentially detectible property in the environment propagated by the food. Strictly speaking, a passing shadow or rustling in the undergrowth etc. are not signals, signs or indicators of impending danger, because they are not deliberately produced, i.e. they are not intentional. They are simply detectable characteristics of the environment that occasionally precede threatening events. As we will see, this fact about the necessary intentionality of signalling is one of the principal weaknesses in mainstream theories of intentionality like Millikan’s. If intentionality is dependent upon representations and representations are dependent upon intention then there is no way to break into the circle.

So, what do we know about the emergence of signalling in a biological context? Or, more to the point, how can a publicly perceptible behavioural trigger (a startle response, say) evolve into an intentional signalling behaviour of the rabbit ground-thumping variety?

In order to answer this question we first need to recognise that vulnerable organisms benefit  from social coexistence because this provides a safer environment in which the probability of attack is greatly reduced. Additionally, when any one individual is attacked, the ensuing commotion has the potential to trigger evasive responses on the part of neighbouring individuals. Any individuals failing to detect and respond to such disturbances will be vulnerable to further attacks and will consequently be less likely to survive.

In order for a behavioural trigger to become a signal then, the following conditions need to be met:

1. A group of organisms must be under selective pressure.
2. These organisms must behave in regular and conspicuous ways when attacked, thereby producing a stimulus with the potential to be used as a signal.
3. Consumers must be capable of detecting the stimulus. 
4. Behaviours triggered by the signal must be advantageous to both producer and consumers in the majority of instances*. 
5. Producers must become capable of producing the signal independent of its standard causes if the signal is to have efficacy over and above that provided by ordinary behaviour.

As can be seen, the steps necessary for even the most basic form of signaling are complex and demand very different circumstances than those that pertain amongst the cell structures of the brain. Quite how an analogous form of signaling, of the kind that Millikan and others impute, could evolve through the interaction of brain cells awaits even the most basic demonstration.

What needs no demonstration though, is the fact that many creatures produce publicly perceptible signals. All that needs to be recognised is that it is the capacity to produce such representations that is instrumental in cases of intentionality, not some alleged but so far entirely undetectable representations flitting around inside our heads.

*Individuals may benefit by “crying wolf” in certain circumstances but the efficacy of this strategy will be limited in the long term. Similarly, withholding a signal may have short term advantages and would explain why many animals respond to alarm calls by increased attention instead of shelter-seeking behaviour.