The problem with Evolutionary Psychology is that it’s easy to construct this sort of “just so” story for pretty much any causal link, and they are not falsifiable.
IMO the simpler hypothesis here is that this isn’t anything adaptive, it’s just another example of how biology is like spaghetti code; changing one chemical signal will affect an essentially random set of downstream systems, some of which can be causally connected to psychology/behavior.
Wildfires are worse in areas where the wrong type of trees were planted as well which is common in logging areas or places cheaply "reforested" that don't do much research on what should be growing there. Wildfires themselves aren't bad per say either as certain trees only grow from fires. Not to say that climate change isn't a factor though, but there are a lot of varibles too.
> you would expect protective social anxiety to arise in people whose situation hasn't much changed except that they've encountered people whose has (as with sedentary villagers encountering nomads who may or may not be about to ransack their settlement).
No, you would not expect that. If rats that self-isolate when their gut micro-biomes change avoid diseases that other rats get afflicted with, then evolution will lead to the mechanism spreading through the rats over time. The rats do not need to know why self-isolating helps, they do not need to even know that self-isolating helps, and they do not need to be in the position where it would help the most.
GP's hypothesis is that diet/environment microbiome changes induce a protective social anxiety. However, a nomadic population - the most likely to exhibit those changes - are successful when exhibiting prosocial or confrontational characteristics, the opposite of social anxiety. Social anxiety is most protective for sedentary groups, who probably should be suspicious of outsiders.
Nothing you said contradicts this, and I'm not sure how to square the circle, even though microbiome-mediated behavior as an explanation for broad, otherwise irrational behavior patterns is attractive.
> IMO the simpler hypothesis here is that this isn’t anything adaptive, it’s just another example of how biology is like spaghetti code; changing one chemical signal will affect an essentially random set of downstream systems, some of which can be causally connected to psychology/behavior.
That's not a competing hypothesis. Obviously the change to the gut affects other things, some of which happen to impact psychology and behavior.
The question is why does this particular change to gut microbiome have such a similar impact on two different species that diverged many tens of millions of years ago? "It just does" is not a very satisfying answer.
That isn't a problem because no one speaks of these suppositions in terms of "just so" but in terms of "could be due to." If you want to prove something as just so you have to do a lot more work describing a mechanism of action and that involves reaching into a different toolbox.
Could also be like climate change, where it correctly describes a broad phenomenon, but cannot be used to identify or classify any individual event. E.g., Wildfires are probably getting worse because of climate change, but it's difficult to say if the Pacific Palisades fire would not have happened in a cooler global climate.
So, is microbiome-mediated social anxiety selected for as an advantageous trait for societies subject to communicable diseases and the travails of nomadism? Maybe. Did YOUR microbiome-mediated social anxiety arise because it was advantageous for your community? Probably impossible to say.
Also, a hole in GP's logic: you would expect protective social anxiety to arise in people whose situation hasn't much changed except that they've encountered people whose has (as with sedentary villagers encountering nomads who may or may not be about to ransack their settlement).