"Humans are just barely intelligent tool users; Darwinian evolutionary selection stopped when language and tool use converged, leaving the average hairy meme carrier sadly deficient in smarts. Now the brightly burning beacon of sapience isn't held by humans anymore – their cross-infectious enthusiasms have spread to a myriad of other hosts, several types of which are qualitatively better at thinking. At last count, there were about a thousand nonhuman intelligent species in Sol space, split evenly between posthumans on one side, naturally self-organizing AIs in the middle, and mammalian nonhumans on the other. ... Conscious civilizations sooner or later convert all their available mass into computronium, powered by solar output. They don't go interstellar because they want to stay near the core where the bandwidth is high and latency is low, and sooner or later, competition for resources hatches a new level of metacompetition that obsoletes them."