Rats are picky eaters who can’t vomit, making them difficult to poison. In WWII, the U.S. tried using a tasteless poison to kill rats. Over 55 blocks in Baltimore, over a million rats were eradicated. Studies then focused on observing rats in controlled environments. In an experiment, overcrowding led rats to engage in violent behavior, neglecting young, and facing high mortality- a ‘behavioral sink.’ This led to discussions about possible parallels with human overpopulation. These macabre findings are now detailed in books about Calhoun’s research and its implications for humanity.
https://www.newyorker.com/magazine/2024/10/07/dr-calhouns-mousery-lee-alan-dugatkin-book-reviews-rat-city-edmund-ramsden-and-jon-adams