Sleep

Humans spend a third of their life sleeping (25 years or more).h Humans can survive longer without food than they can without sleep.e During the first two years of a baby’s life, new parents will miss six months of sleep on average.e In 1894, Russian scientist Marie Mikhaïlovna de Manacééne conducted one of the earliest experiments on extreme sleep deprivation. She found that when she deprived puppies of sleep, they all died within four or five days, despite every effort to keep them alive. The younger the puppy, the more quickly it died.k Giraffes sleep just 1.9 hours a day while koalas sleep up to 22 hours a day Giraffes sleep only 1.9 hours a day in five- to 10-minute sessions. Koalas, however, are the longest-sleeping mammals, sleeping up to 22 hours a day.a,b The word “sleep” derives from the Proto-European base *sleb, “to be weak,” and is related to “slack.” “To sleep around” was first recorded in 1928.j Sleep is a universal characteristic of complex living organisms and has been observed in insects, mollusks, fish, amphibians, birds, and mammals.f Only one half of a dolphin’s brain goes to sleep at a time. Dolphins are capable of what is known as unihemispheric sleep, in which one hemisphere of the brain goes into a deep sleep while the other hemisphere remains awake. This allows dolphins to sleep under water without drowning. Dolphins spend approximately one third of their lives asleep.k Slow-wave sleep appeared about 180 million years ago. REM sleep is believed to have appeared 50 million years later. Humans most likely developed a monophasic sleep/wake pattern in the Neolithic period (10,000 B.C.).k In Greek mythology, Hypnos (Somnus in Roman mythology) was the god of sleep. Thanatos, or death, was his twin. Poppies and other sleep-inducing plants grew at the entrance of Hypnos’ cave.k