Scaling immunity: sickness as a host defense strategy, 2026, Sparling

[Jonathan Edwards]

It could also not be an evolved trait to improve survival.

We tend to assume that all such things evolve through conferring survival. I find it hard to see how such a complex set of physiologic changes could be epiphenomenal. And if you block TNF, for instance, whch is a major 'sickness behaviour' mediator, in infection you get a massive increase in death rate. Anti-TNF infliximab was invented for sepsis and turned out to be a disaster. Luckily it was rather good for rheumatoid arthritis.

 

[Creekside]

We tend to assume that all such things evolve through conferring survival.

Yes, but it could be the result of multiple factors evolving for their specific benefits (increasing transport of a certain molecule into a certain cell type, for example), rather than with a broad goal of "keeping the victim from being active". Studies might show that acting on sickness behaviour (staying in bed) does increase survival by >.3%, but that doesn't prove that it's an evolved and important trait for recovery. Nit-picking perhaps, but it might be the difference between funding research identifying specific mechanics of the body's responses to viral infection, and funding development of a drug to make you feel too lousy to get out of bed (because staying in bed is the important part) or funding BPS treatments based on thinking yourself out of bed or some such thing.