Great post. As you point out, this is one of the important unresolved questions in science, and much more research aimed at generating relevant evidence is needed.
Meanwhile, I find the evolutionary perspective especially useful at this stage, so I wanted to raise one disagreement with the claim that there is “every evolutionary reason” for relatively simple organisms to feel intense pain. The adaptive value of a rapid and dramatic response does not, by itself, tell us how intense the underlying felt state must be. Reflexive behavior, for example, can be rapid and dramatic without involving affective experience at all. Even in a sentient organism, a strong behavioral response could be triggered by a low response threshold rather than by an extremely intense felt state.
Framed as a cost–benefit question, I therefore do not think evolutionary reasoning alone makes high-intensity pain in simpler sentient organisms the parsimonious default. We explored that broader perspective here.
Briefly, affective scales help organisms prioritize among competing needs and actions. Organisms with simpler nervous systems are expected to have more limited behavioral repertoires and fewer competing motivations, in which case a lower-resolution affective scale may be sufficient. Organisms with richer behavioral and cognitive repertoires, by contrast, needs to integrate a much larger set of memories, sensory inputs, and competing priorities.
Lower resolution does not by itself imply a narrow affective range. But expanding the range to include extreme states is only one possible way of producing urgent behavioral prioritization. All else being equal, selection should favor a less costly mechanism when it provides the same functional benefit. Very high affective intensity probably involves additional energetic, physiological, or architectural demands
Taken together, these considerations do not rule out intense pain in insects or decapods. But evolution makes high-intensity pain an important hypothesis to investigate, not a default conclusion (We explored the distinction between affective range and resolution more directly here).
Great post. As you point out, this is one of the important unresolved questions in science, and much more research aimed at generating relevant evidence is needed.
Meanwhile, I find the evolutionary perspective especially useful at this stage, so I wanted to raise one disagreement with the claim that there is “every evolutionary reason” for relatively simple organisms to feel intense pain. The adaptive value of a rapid and dramatic response does not, by itself, tell us how intense the underlying felt state must be. Reflexive behavior, for example, can be rapid and dramatic without involving affective experience at all. Even in a sentient organism, a strong behavioral response could be triggered by a low response threshold rather than by an extremely intense felt state.
Framed as a cost–benefit question, I therefore do not think evolutionary reasoning alone makes high-intensity pain in simpler sentient organisms the parsimonious default. We explored that broader perspective here.
Briefly, affective scales help organisms prioritize among competing needs and actions. Organisms with simpler nervous systems are expected to have more limited behavioral repertoires and fewer competing motivations, in which case a lower-resolution affective scale may be sufficient. Organisms with richer behavioral and cognitive repertoires, by contrast, needs to integrate a much larger set of memories, sensory inputs, and competing priorities.
Lower resolution does not by itself imply a narrow affective range. But expanding the range to include extreme states is only one possible way of producing urgent behavioral prioritization. All else being equal, selection should favor a less costly mechanism when it provides the same functional benefit. Very high affective intensity probably involves additional energetic, physiological, or architectural demands
Taken together, these considerations do not rule out intense pain in insects or decapods. But evolution makes high-intensity pain an important hypothesis to investigate, not a default conclusion (We explored the distinction between affective range and resolution more directly here).
Good to debate this topic!