John Calhoun's Universe 25 (1968–1973): 8 mice placed in a enclosure with unlimited food, water, and nesting space. No disease, no predators. A literal utopia.

What happened:

🔵 Normal mice reproduced normally at first

🔴 Aggressive mice emerged as density increased — disrupting social hierarchies

🟡 "Beautiful Ones" appeared — mice that completely withdrew from society, spending all day grooming, never fighting, never mating

📉 Once the Beautiful One fraction crossed \~25%, reproduction essentially stopped — even as population dropped and space opened back up

Calhoun's key finding: the collapse was behavioral, not resource-based. Mice raised during the chaos never learned normal social behaviors. Even with plenty of space and food, they couldn't recover.

This simulation models the stress-cascade and state transitions he described. Built in Python with NumPy.

Full 10-minute simulation: [https://youtu.be/wXfq6jY00Lk](https://youtu.be/wXfq6jY00Lk)

In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end.