I've been thinking recently about group organisms and group minds. And I've been thinking, too, about the Fermi Paradox -- about why we haven't yet discovered alien civilizations, given the vast number of star systems that could presumably host them. Here's a thought on how these two ideas might meet.
This is, of course, a version of the self-destruction solution to Fermi's paradox: Technological civilizations might frequently arise in the galaxy, but they always destroy themselves quickly, so none happen to be detectable right now. Self-destruction answers to Fermi's paradox tend to focus on the likelihood of an immensely destructive war (e.g., nuclear or biological), environmental catastrophe, or the accidental release of destructive technology (e.g., nanobots). My hypothesis is compatible with all of those, but it's also, I think, a bit different: A single superorganism might die simply of disease (e.g., a self-replicating flaw) or malnutrition (e.g., a risky bet about next year's harvest) or suicide.
For this "solution" -- or really, at best I think, partial solution -- to work, at least three things would have to be true:
(1.) Technological civilizations would have to (almost) inevitably merge into a single superorganism. I think this is at least somewhat plausible. As technological capacities develop, societies grow more intricately dependent on the functioning of all their parts. Few Californians could make it, now, as subsistence farmers. Our lives are entirely dependent upon a well-functioning system of mass agriculture and food delivery. Maybe this doesn't make California, or the United States, or the world as a whole, a full-on superorganism yet (though the case could be made). But if an organism is a tightly integrated system each of whose parts (a.) contributes in a structured way to the well-being of the system as a whole and (b.) cannot effectively survive or reproduce outside the organismic context, then it's easy to see how increasing technology might lead a civilization ever more that direction -- as the individual parts (individual human beings or their alien equivalents) gain efficiency through increasing specialization and increased reliance upon the specializations of others. Also, if we imagine competition among nation-level societies, the most-integrated, most-organismic societies might tend to outcompete the others and take over the planet.
(2.) The collapse of the superorganism would have to result in the near-permanent collapse of technological capacity. The individual human beings or aliens would have to go entirely extinct, or at least be so technologically reduced that the overwhelming majority of the planet's history is technologically primitive. One way this might go -- though not the only way -- is for something like a Maynard Smith & Szathmary major transition to occur. Just as individual cells invested their reproductive success into a germline when they merged into multicellular organisms (so that the only way for a human liver cell to continue into the next generation is for it to participate in the reproductive success of the human being as a whole), so also human reproduction might become germline-dependent at the superorganism level. Maybe our descendents will be generated from government-controlled genetic templates rather than in what we now think of as the normal way. If these descendants are individually sterile, either because that's more efficient (and thus either consciously chosen by the society or evolutionarily selected for) or because the powers-that-be want to keep tight control on reproduction, then there will be only a limited number of germlines, and the superorganism will be more susceptible to shocks to the germline.
(3.) The habitat would have to be small relative to the superorganism, with the result that there were only one or a few superorganisms. For example, the superorganism and the habitat might both be planet sized. Or there might be a few nation-sized superorganisms on one planet or across several planets -- but not millions of them distributed across multiple star systems. In other words, space colonization would have to be relatively slow compared to the life expectancy of the merged superorganisms. Again, this seems at least somewhat plausible.
To repeat: I don't think this could serve as a full solution to the Fermi paradox. If high-tech civilizations evolve easily and abundantly and visibly, we probably shouldn't expect all of them to collapse swiftly for these reasons. But perhaps it can combine with some other approaches, toward a multi-pronged solution.
It's also something to worry about, in its own right, if you're concerned about existential risks to humanity.