Human Extinction Could Be Imminent, Mouse Experiment Suggests

In 1968, Dr John B Calhoun, a behavioural researcher at the US National Institute of Mental Health (NIMH), began a groundbreaking study that may hold chilling warnings for humanity's future. Nicknamed Universe 25, officially titled the "Mortality-Inhibiting Environment for Mice", the experiment placed mice in a sealed, predator-free habitat measuring 4.6 feet (1.37 m) per side, stocked with unlimited food, water, nesting material, and climate control. The enclosure featured 256 nest boxes linked by mesh tunnels, creating a supposed rodent paradise, but what unfolded hinted at the potential path to human extinction.

Universe 25 began with just eight healthy albino mice, four male and four female. After about 3 and half months, the first offspring were born. Thereafter, the mice population doubled every 55 days. 

By around month 19, the population peaked at approximately 2,200 mice. Despite the environment being capable of supporting up to 3,800-4,000 mice, reproduction began to slow as density increased. 

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With overcrowding came social breakdown. Young male "dropouts" unable to attain dominance amassed in the pen's centre, often engaging in violent brawls. Dominant males could no longer protect females, who in turn neglected or attacked their young. Females abandoned litters before weaning; some even turned aggressive towards their pups. 

Abnormal behaviours intensified: females isolated themselves, while certain males, termed "the beautiful ones", spent their days grooming, eating, and sleeping but avoided mating or social interaction. This phenomenon was described by Calhoun as the "behavioural sink", a collapse of social behaviour under extreme overcrowding. 

As social pathology increased, births ceased within about 600 days of the experiment's start, and the population rapidly declined toward extinction. By the early 1970s, all the mice in Universe 25 had died.