Reminds me of Calhoun's Mouse Utopia experiments: "Other young mice growing into adulthood exhibited an even different type of behavior. Dr. Calhoun called these individuals “the beautiful ones.” Their time was devoted solely to grooming, eating and sleeping. They never involved themselves with others, engaged in sex, nor would they fight. All appeared [outwardly] as a beautiful exhibit of the species with keen, alert eyes and a healthy, well-kept body. These mice, however, could not cope with unusual stimuli. Though they looked inquisitive, they were in fact, very stupid."
Like many psychology and sociology papers, Mouse Utopia is now discredited because nobody could reproduce those results: https://www.gwern.net/Mouse-Utopia
"Kessler 1966 only somewhat resembles Calhoun’s results: while Kessler does describe deviant mice behavior driven by density (such as homosexual matings) and high infant mortality/cannibalism, on the other hand, there are no population crashes or cessation of reproduction but stable populations after initial growth, there are no behavioral sinks, any ‘beautiful ones’ or ‘drinkers’ or ‘autistic’ mice are not described as such by Kessler, the mice are healthy overall, and transplanted mice revert"
https://fee.org/articles/john-b-calhoun-s-mouse-utopia-exper...