Eventually other deviant behavior emerged. Mice who had been raised improperly or kicked out of the nest early often failed to develop healthy social bonds, and therefore struggled in adulthood with social interactions. Maladjusted females began isolating themselves like hermits in empty apartments - unusual behavior among mice. Maladjusted males, meanwhile, took to grooming all day-preening and licking themselves hour after hour. Calhoun called them "the beautiful ones." And yet, even while obsessing over their appearance, these males had zero interest in courting females, zero interest in sex.
Intriguingly, Calhoun had noticed in earlier utopias that such maladjusted behavior could spread like a contagion from mouse to mouse. He dubbed this phenomenon "the behavioral sink."
Between the lack of sex, which lowered the birth rate, and inability to raise pups properly, which sharply increased infant mortality, the population of Universe 25 began to plummet. By the 21st month, newborn pups rarely survived more than a few days. Soon, new births stopped altogether. Older mice lingered for a while-hiding like hermits or grooming all day-but eventually they died out as well. By spring 1973, less than five years after the experiment started, the population had crashed from 2,200 to 0. Mouse heaven had gone extinct.
Recently, however, human birth rates have dropped sharply in many developed countries-often below replacement levels- and young people in those places have reportedly lost interest in sex. The parallels to Universe 25 seem spooky.
