I'm having some malaise today after my second shingles vaccine, and the thought struck me that malaise may have an evolutionary basis in decreasing mobility of sick individuals to limit spread of infectious disease, or perhaps even to slow down sick prey so they (and their genes) are culled from the herd.
Sure enough, someone has theorized this. It took me down a wormhole to, believe it or not, autism and Neanderthals.
"there is a method to the madness, beginning with the need to survive in a hostile microbial environment in ancestral times, and ultimately resulting in the legacy of an inflammatory bias which when triggered or fostered by environmental conditions can lead to a host of maladies that are overrepresented in the modern world including allergic disorders, cardiovascular disease, diabetes, cancer and neuropsychiatric disorders..."
"From the behavioral side, reorganization of priorities to fighting infection and wound healing requires reduced exploratory behavior...as well as hypervigilance against future attack...Thus, as the immune and nervous systems developed hand-in-hand through evolutionary time, it should not be surprising that one of the consequences of our bias to inflammatory responses is a vulnerability to behavioral disorders that are coupled to inflammation including reduced exploratory behavior in the form of depression and hypervigilance in the form of anxiety. In support of this notion are recent data indicating that depression risk [genes] are regularly associated with immune responses to infection that were likely to enhance survival in the ancestral environment..."
"the infection-defense hypothesis not only incorporates the above noted advantages of energy conservation through the depressive symptoms of anhedonia, social withdrawal, fatigue and psychomotor retardation but also invokes the impact of depressive behaviors on reducing exposure to further challenge from infectious or other environmental stressors as well as decreasing the spread of infection to social conspecifics..."
"depression is associated with decreased concentrations of oxytocin...a molecule believed to be intimately involved in social relationships, thereby reducing the spread of infection through inhibitory effects on molecular pathways that mediate social attachment..."
"healthy volunteers administered endotoxin and typhoid vaccination have revealed that in the context of an inflammatory stimuli, multiple brain regions are involved in behavioral change including the basal ganglia and limbic regions..."
The paper goes on to elaborate on the links between infection/inflammation in early childhood and subsequent depression, schizophrenia, and autism.
Malaise, Melancholia and Madness: The Evolutionary Legacy of an Inflammatory Bias
One more curious fact in this paper, that we get our immune prowess from Neanderthals: "data suggest that European and Asian peoples were the beneficiaries of a critical immunologic boost through interbreeding with Neanderthals...genes derived from Neanderthals* that cluster in the human major histocompatibility locus and are associated with a more aggressive immune response to pathogens including viruses."
* I also didn't realize that actual Neanderthal DNA has been found and sequenced. "DNA extracted from Late Pleistocene remains make its study challenging. The DNA is invariably degraded to a small average size of less than 200 base pairs" - https://science.sciencemag.org/content/328/5979/710.full
And the extent of Neanderthal DNA in our genome has been extrapolated by statistical means "They developed a statistical approach to identify genetic signatures suggestive of Neanderthal ancestry in the genomes of 379 European and 286 East Asian individuals." - https://www.google.com/amp/s/www.the-scientist.com/features/neanderthal-dna-in-modern-human-genomes-is-not-silent-66299/amp
A good discussion of the science of Neanderthal DNA from the Smithsonian included this interesting discovery: " Because Neanderthals likely evolve outside of Africa (no Neanderthal fossils have been found in Africa to date) it was thought that there would be no trace of Neanderthal DNA in African modern humans. However, a study in 2020 demonstrated that there is Neanderthal DNA in all African Homo sapiens (Chen at el., 2020). This is a good indicator of how human migration out of Africa worked: that Homo sapiens did not leave Africa in one or more major dispersals, but that there was gene flow back and forth over time that brough Neanderthal DNA into Africa."
https://humanorigins.si.edu/evidence/genetics/ancient-dna-and-neanderthals
Also from that article, both Neanderthals and humans developed pale skin: " Vitamin D is synthesized when the sun’s UV rays penetrate our skin... Therefore, it would be beneficial for populations in colder climates to have paler skin so that they can create enough vitamin D even with less sun exposure."
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