A story on NPR examines "social jet lag", an obscure phenomenon in which people stay up late and sleep in late on the weekends ("Jet-Lagged By Your Social Calendar? Better Check Your Waistline").
"Unfortunately, we have caveman's hard-core wiring," Emsellem says, "and insufficient sleep in primitive times was read by the body: Danger, store fat," she says.
Aaaack! So toddlers and the elderly are nature's chosen people, and ... oh, I can't even finish that thought. If I read one more time about the hard-core wiring of cavemen, I'm going to unleash the Morlock horde on these people.