Affectivity as a Biological Fitness Function
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Producing Adaptive Behavior: Affectivity & Sensitivity
To make sense of representation we have to dig deeper into adaptive behavior. How, precisely, is it that our kind manages to produce adaptive behavior? In humans, adaptive behavior is largely driven by affectivity, an evolutionary development we share with the rest of the animal world. Affectivity is the ability to produce an affective response (also known simply as "affect"), an embodied, one-dimensional feeling that is elicited continuously as we live and interact with our environments; it ranges from pleasant to unpleasant in different intensities. When they arise, biological imbalances like thirst and hunger elicit negative affect, a coercive and unpleasant feeling that demands action take place to make it go away. Negative affects are also elicited when we interact with the environment in injurious ways, motivating corrective action that helps us stay out of harm's way. In contrast, positive affects are pleasant feelings that signal well-being; they arise from interactions with biologically significant elements and are our only positive indication that whatever is happening is good for us.
We can think of affectivity as an embodied fitness function, a felt sense of adequacy and harmony with our surroundings.
As a force that motivates adaptive behavior, affect is of great adaptive value. Although far from perfect, it is our "way of knowing" if something ought to be done; it rewards behavior that tends to be adaptive while punishing behavior that tends to be maladaptive. I discussed human affect in Experiential Costs:
“Human affect (...) makes situations either costly to endure or rewarding to have. Affect, in a way, turns experience into a cost function, but one that you can feel. I want to stress that. A cost function takes some input and returns a value that somehow represents the cost or reward associated to the input. The higher the absolute value of it is, the higher the cost or the reward obtained. Similarly, the cost function of your experience takes the situation you are living as input but, instead of returning a value, it returns a feeling. This feeling, or affect, can be costly or rewarding to have and constitutes a primary appraisal of the experience you are having.”
The emergence of affective responsiveness in animals tells us that at some point during the evolution of biological forms, survival and behavior stopped being random processes. At this turning point, behavior stopped being merely "something that happens" to become something that happens towards something — behavior became a directed process. Instead of a random walk in which only a few roads led to survival, organisms started taking a safer route directing their behavior towards the objects of survival (e.g., food, water, minerals, shelter). But to get a sense of where these biologically significant elements might be found, affectivity is not enough: While it is certainly important for a creature to know whether it has found food or shelter, it is of equal or greater relevance they know when they encounter something that isn't food nor shelter but merely signals their proximity. To direct their behavior towards the objects of survival, organisms had to develop sensitivity to the objects and stimuli associated with them. Consider, for the sake of illustration, the sensitivity developed by spiders to mechanical vibrations: To the web-spinning spider, vibrations are intimately associated with feeding as they indicate a victim has been snared on the web and provide a sense of direction that can be used to locate the victim. Spiders also use vibrations to stay clear of predators, using hair-like structures on their legs to detect the chirp of hunting birds or the flapping wings of larger insects.
Sensitivity is the ability to respond to signals, to "see behind" what is presented to us.
Sensitivity is of great adaptive value because it lets organisms use objects and stimuli of indirect biological significance (positive or negative) to trigger and direct behavior. Developing sensitivity speaks of a higher adaptedness to the environment and a familiarity to the patterns in which it delivers bounty and hazard. Together with affectivity, it gives animal forms their distinctive liveliness and responsiveness.