Summary

Humans sleep for approximately a third of their lives, yet we have yet to figure out why, Bryson writes in Chapter 16. Every part of the body benefits from sleep and being deprived of sleep will eventually kill a person. In 1989 researchers at the University of Chicago did a cruel experiment in which they deprived rats of sleep. They died between 11 and 32 days after the experiment started. Although people have long believed that sleep consolidates or transfers memories, researchers say there is little evidence for this. Researchers have found evidence that almost all animals sleep, although the amount each animal needs varies. Elephants and horses sleep only two or three hours a night, while sloths sleep for about 10 hours.

Much of what we know about sleep comes from Eugene Aserinsky, a sleep researcher at the University of Chicago who, in 1951, measured his 8-year-old son...