There is the opinion of some scientists that intelligence was brought to Earth by extraterrestrial civilizations. Moreover, the aliens, allegedly, conducted experiments with the genome of not only primates (future humans), but also rats.
Rats are very similar in structure to humans, and not only physically, they have almost the same genome. It is not surprising that these small predators are distinguished by their excellent intelligence.
It is for this reason that rats were taken as a starting material for the creation of combat super-creatures that can survive in any conditions and at the same time be invisible to the enemy. In order to create such a "biological weapon", in 1929 a secret laboratory appeared in the USSR in Saratov. But this case was never brought to an end, although in fifty years the rats were made into real mutant killers. And when, before the collapse of the USSR, it was decided to close the laboratory and destroy all the experimental animals, the rats were simply not found. The rats somehow knew that they would eventually want to be exterminated, and over the years they gnawed through a multi-meter concrete wall, making a hole for retreat into the sewer.
It was at that time (1989-1990) that terrible and incredible news about mutant rats in the Moscow metro appeared in the media, and not only in the metro and not only in the capital. Today, many researchers are sure that those artificially bred rats went to the "underground floors" of the largest cities and created their own civilization there with certain laws, hierarchy and even a kind of culture.
For more information on this, as well as how the rats saved humanity from the second "black plague" and at the same time almost destroyed the besieged Leningrad, watch the video. Let us add only in conclusion that "rattus sapiens" - a rational rat - is a completely possible option for the further development of civilization on our planet.