WILD ANIMALS
Pain acts as an alarm system, helping to safeguard animals from bodily harm. However, chronic pain and other pain disorders negatively affect the physical and mental health of animals. Greater pain tolerance has improved the evolutionary success of some species to such an extent that they may have completely lost sensitivity to certain noxious stimuli.
Several mole-rat species have naturally evolved insensitivities to otherwise painful stimuli (Smith et al., 2020). They show no signs of distress when exposed to acids and capsaicin (Lewin et al., 2021; Smith et al., 2020), nor develop thermal hyperalgesia after inflammation (Park et al., 2008).
Scorpion venom usually induces intense pain, but grasshopper mice turn venom into painkillers via an act of molecular aikido. Instead of agony, they reverse the action of the venom to actually block pain signaling (Rowe et al., 2013).
Many birds lack sensitivity to capsaicin also (Mason et al., 1991). ​The existence of thriving animals, including humans, who experience dramatically less pain and suffering indicates that eliminating chronic and other types of pathological pain can be done without harming animals' ability to protect themselves. Similar adaptative reductions in pain can be achieved through selective breeding.​