Probing the need for sleep.

• Position: SCIENCE - Brief Article - Illustration

To better understand why we humans sleep as we do--and why sleep even exists--scientists are examining the slumber habits of a wide range of animal species.

HOURS OF EYE POSITION ANIMAL SLEEP PER DAY DURING SLEEP Hairy armadillo 20.4 * * both closed Brown bat 19.9 * * Southern opossum 19.4 * * Ground squirrel 14.5 * * Domestic ferret 14.5 * * Mountain beaver 14.4 * * Burrowing owl 14.3 * ** one eye sometimes open Cat 13.2 * * Pigeon 11.9 * ** Domestic...