[Epistemic status: Thinking out loud; copying my EA Forum comment about these papers from a couple weeks ago]

If the evolutionary logic here is right, I'd naively also expect non-human animals to suffer more to the extent they're (a) more social, and (b) better at communicating specific, achievable needs and desires.

There are reasons the logic might not generalize, though. Humans have fine-grained language that lets us express very complicated propositions about our internal states. That puts a lot of pressure on individual humans to have a totally ironclad, consistent "story" they can express to others. I'd expect there to be a lot more evolutionary pressure to actually experience suffering, since a human will be better at spotting holes in the narratives of a human who fakes it (compared to, e.g., a bonobo trying to detect whether another bonobo is really in that much pain).

It seems like there should be an arms race across many social species to give increasingly costly signals of distress, up until the costs outweigh the amount of help they can hope to get. But if you don't have the language to actually express concrete propositions like "Bob took care of me the last time I got sick, six months ago, and he can attest that I had a hard time walking that time too", then those costly signals might be mostly or entirely things like "shriek louder in response to percept X", rather than things like "internally represent a hard-to-endure pain-state so I can more convincingly stick to a verbal narrative going forward about how hard-to-endure this was".

Wow, this is fascinating speculation, thanks for posting.

The section on pain varying with the social environment was especially interesting. It reminded me of the (common but not uncontroversial) parenting strategy whereby babies are left to cry at night, so as to avoid positively reinforcing crying and instead train them to sleep unaided.

Would it suggest that exhortations to 'stop being a wuss' were actually effective? The nearby people are effectively precommitting to not be moved by visible suffering, which might reduce the incentive for the victim to experience pain.

To me this is interesting evidence suggesting that one purpose of pain in humans is to be visible (attracting help). It doesn't go very far to suggest that this is pain's only purpose, which I think is what would be needed for me to hypothesize that solitary animals feel little or no pain.

I'm currently in school for physical therapy assisting; as you might imagine, pain is a big topic for us! The standard hypothesis we've been taught is that pain is most typically experienced as a signal to the person experiencing it that something needs to be done. (This is the model where the pain you feel on burning your hand is what causes you to take it off the hot stove—or more accurately, what causes you not to put your hand right back on the stove, because you've probably had a reflex reaction that removed your hand from the hot stove before the signal reached your conscious awareness.) It's easy to see how in humans "something needs to be done" can include a much broader range of behaviors than simply moving away from something unpleasant, avoiding immediate weight-bearing on a sprained ankle, etc. But the pain is already useful even if the reaction to it is smaller. If you've sprained your ankle, it's a good idea to be a bit more sedentary than usual the next day even if you never cry and try hard not to limp. It seems to me like a lot of animals that we think of as showing less pain may show it in subtle behavioral ways that would not be noticeable to their typical predators. (These may also be harder to observe in situations that don't allow for normal behavior, such as a laboratory.)

But you're right that pain is very complicated, and it doesn't always correspond to tissue damage, especially in the case of chronic pain. It may be that some situations in which humans feel pain have evolved specifically in tandem with our complex social behavior. I would just be very wary of extending that to acute pain in general, which does seem to be strongly associated with tissue damage in humans in a broad variety of cases—and for which there is often a direct physical response the pain seems adapted to provoke.

Physical damage which is self-induced is less painful. They give as examples “runner’s high”, cosmetic procedures like hair removal, and self-harm.

I wonder how certain we are that this is about pain levels, rather than the addition of emotions like uncertainty or alarm to pain that comes from others. If I knowingly cut myself with a knife, I'm ready for the pain; I can predict what will happen and steel myself. If someone else cuts me with a knife, I'm not prepared in the same way, and many other negative emotions are going to be flooding my system.

This makes me wonder whether accidental self-harm is more painful than purposeful self-harm (e.g. I cut myself while cutting up vegetables). If not, evidence for social factors mediating pain; if so, evidence for the role of surprise.

Thanks for writing this.

How would this model explain Cluster Headaches? They are not particularly more incapacitating than migraines, yet they are (possibly literally*) thousands of times more acutely painful than them. What is the role of this X1000 multiplier on phenomenal pain in such cases? As far as I can tell, in the ancestral environment nobody could have done anything to help you if you were having a Cluster Headache, and your chances of reproduction seem to be the same whether that pain was a thousand times less bad (which would still be VERY bad, but not in the level of ultra-Hellish pain). In particular, other species are known the have Cluster Headaches too, such as cats. So perhaps we should cluster pains into two buckets - those that have social significance and those that don't. I worry that this study will make people dismiss extreme suffering in nonhuman animals, but that should only really apply to socially-useful pains. I suspect that there are many species-specific ultra-painful experiences that we will not discover (and prioritize!) unless we look for them.

*See: https://forum.effectivealtruism.org/posts/gtGe8WkeFvqucYLAF/logarithmic-scales-of-pleasure-and-pain-rating-ranking-and

I think it's worth qualifying these statements with "all else equal".

But note that all else is not equal. Humans, having greater capacity to reason and make predictions, can probably anticipate pain (and its end) and negative outcomes better. This could cause anticipatory anxiety, but it could also help us avoid pain in the first place, or rationalize our pain. Nonhuman animals have to rely much more directly on their pain signal reinforcement. So is the pain signal more useful to us or to them? I don't think the answer is clear either way.

Also, don't forget that we're attempting interpersonal utility comparisons. If we scaled up the intensity of all experiences without affecting how an animal behaves, we wouldn't be able to tell the difference.

This is a fascinating idea! I have a question though. I'm not exactly sure why (2) (more women have chronic pain, less pain tolerance etc) is evidence for this. Is the idea that women in the ancestral environment were more in need of assistance (eg because they were physically weaker, or made more vulnerable by bearing/raising children), and therefore evolved more capacity to feel (and thus express) pain?