Thought this might be of interest. https://academic.oup.com/rheumatolo...tract/doi/10.1093/rheumatology/kez027/5366191 Sci Hub, https://sci-hub.tw/https://academic...tract/doi/10.1093/rheumatology/kez027/5366191
While pain is usually regarded as a fairly somatic phenomenon, both fatigue and depression have traditionally been regarded as more-or-less of psychological origin. Goodness knows what that is supposed to mean or where it come from. The idea that depression is of psychological origin suggests that the authors don't really know what they mean by their basic terms. The stuff about evolution, multifaceted.. deeply conserved ... seems like the usual recycled drivel.