Biochemistry Volunteers
Wild Animals Lacking Pain
Pain is the evolutionary alarm system that protects organisms from bodily harm. But pain and suffering aren't always the dynamic duo that they're made out to be. It's not just plants, fungi, and surgical patients that benefit from a lack of pain. Indeed, lacking pain can actually enhance the physical health, welfare, and even evolutionary fitness of animals.
Several naked mole-rat (Heterocephalus glaber) 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 signalling (Rowe et al., 2013).
Many birds lack sensitivity to capsaicin too (Mason et al., 1991).
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But tunicates by far, have the strangest method for opting out of pain. Also known as sea squirts, these bizarre creatures offer a glimpse into early animal evolution, straddling their lives between a conscious mobile stage and a mature but vegetable-like animal.
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Adult sea squirts with skeletons leftover from the tadpole stage.
Sea squirts are, indeed, otherworldly, as they absorb their own central nervous systems when converting from their tadpole-like developmental stage into mature and immobile filter feeders. In doing so, they lose any capacity for subjective experience attributable to these tissues (Okamura et al., 2005; Zaniolo et al., 2002).
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The existence of thriving animals, including humans, who experience dramatically less suffering, gives us pause to question our long-held beliefs. For example, a Buddhist might maintain that suffering is a "Noble Truth," but these examples demonstrate that it is certainly not a universal one.