there’s a hypothesis that long-duration pain, the kind of pain that lasts after the abrupt piercing of flesh, is not universal to the animal kingdom. almost all animals need to be able to react to immediate negative stimuli, and do, and so they have the kind of pain receptors necessary to tell them if something is attacking them or hurting them to flee. but for animals which are not sociable, which do not care for one another, and which therefore must nurse their wounds alone, to continue to feel intense pain after the immediate threat has passed would only weaken and distract them. longer-duration pain, extended suffering, is a consequence of our ability to express pain to others, adaptive only for animals who have mothers or siblings or other conspecifics who will come to their aid when danger threatens.