3 ultimate causes for excessive pain

If you want deep explanations for pain, you have to stare into the abyss of deep time and biology. Todd Hargrove did: in a post I missed last year, he explored the ways an evolutionary perspective might shed light on why pain sometimes transmogrifies from a useful alarm system into something that seems to be disconnected from reality, pain that’s too strong and goes on for too long, for no apparent reason, formally known as “nociplastic” pain.

“One of [evolutionary medicine's] goals is to provide “ultimate” explanations for disease as opposed to merely “proximate” explanations. This is the difference between understanding why disease happens versus just how.”

He mainly frames the “why” of pain as a defence mechanism that motivates protective behaviours, a principle that is famously demonstrated by how badly things go for animals that can’t feel pain. We hurt because we must; life breaks without it. (Nerdy note: The physiology is what adapts and evolves to serve a “purpose,” while pain is what we feel and experience. They aren’t the same, but I’m conflating them for clarity here.)

Humans are unusual animals, and we have more high-level processing involved in our self-defence systems. For instance, we probably extend it to emotional pain — anxiety, depression — because that may also serve defensive or adaptive purposes, like avoiding social rejection or infection, or strategic withdrawal in the face of loss or failure.

A circular cladogram, a better symbol for evolution than the problematic “March of Progress” image. • This diagrams shows millions of species and tens of thousands of distinct evolutionary trees, all meticulously merged here, representing all 2.3 million named species (as of 2015). But Earth has about 8.7 million species, with about 15,000 still being identified annually. And most of them, if not all, have some kind of pain system — because pain is fundamental to life, a “highly conserved” feature of biology. (Credit: Stephen Smith, “Synthesis of Phylogeny and Taxonomy into a Comprehensive Tree of Life,” by Cody E. Hinchliff et al., PNAS, 2015.)

“It’s a defence mechanism” is a broad principle that doesn’t explain pain that seems glitchy. Hargrove suggests three ways an evolutionary perspective may help to explain why pain (and emotional suffering) may become excessively intense or persistent:

1. One possibility is the “smoke detector principle”: natural selection just favours hypersensitive defences to avoid catastrophic mistakes.
2. Another is “evolutionary mismatch” — modern life overstimulates systems tuned for ancestral environments (although there are many problems with some of the most popular speculative examples).

3. Advanced adaptive systems like pain and immunity come with built-in vulnerabilities, including the risk of dysfunction. In other words, you can't get robust benefits without complications and impossible dilemmas …

   “If the immune system gets more active it will get better at killing infections, but it all also make us sick more often and increase the risk for auto-immune diseases. A pain system that can modulate its sensitivity level (increasing sensitivity after an injury, and then returning to baseline after healing) provides a great benefit in fine-tuning the sensitivity to meet the circumstances. But it also runs the risk of getting ‘stuck’ in the sensitized position if the system becomes dysregulated or confused in how it processes information related to threat.”