"By day 560, the mouse population reached 2,200, and then steadily declined back down to unrecoverable extinction. Few females carried pregnancies to term, and the ones that did seemed to simply forget about their babies. They'd move half their litter away from danger and forget the rest. Sometimes they'd drop and abandon a baby while they were carrying it."
-- Dr. John B. Calhoun's 'Mouse Utopia' experiment