Elephants only sleep two hours a night

By Ross Pomeroy
Real Clear Wire

The study was quite the sensation when it was published in March of 2017. Scientists affiliated with University of the Witwatersrand in South Africa tracked African elephants in the wilds of Botswana for a month straight, and found that they only slept for two hours per day on average. What’s more, the animals could skip a night's sleep without needing extra naps the next day. Huh? How? Could we learn to sleep like that?

Alas, elephants' amazingly efficient sleep schedule is likely unique to them, not something humans could adopt through scientific means.

The study further evinced a trend that extends across the mammalian class: the bigger the mammal, the less sleep it needs. 

Some of the tiniest bats routinely sleep 18 hours a day. Cats sleep between 12 and 16. Chimpanzees doze about 10 hours. Cows snooze for about four. Yes, there are exceptions here and there – prey animals sleep less, predators more – but the trend is pretty consistent.

One of the tidiest theories to explain it was proposed almost two decades ago, and it has held up remarkably well. Scientists Van Savage and Geoffrey West at the Santa Fe Institute speculated that, "the process identified as sleep is a special state of the brain that is devoted primarily to the critical activities of repair and reorganization." Other organs and tissues could be repaired when awake, but not the brain.

Larger mammals thus need fewer hours of sleep because they have slower metabolisms than small mammals. This fact follows a biological law called Kleiber's Law, named for the biologist who discovered it. The law states that for the vast majority of animals, an organism's metabolic rate scales to the 3⁄4 power of its body mass. Pound for pound, smaller animals consume more energy.

This applies to all tissues and organs, even the brain. Each cell in the half-gram brain of a mouse demands more energy than a comparable cell inside a five kilogram elephant brain. Smaller brains thus produce proportionally more waste products and become more 'damaged' during operation per unit mass than large ones, requiring more time asleep to get them back into working order.

"The theory is able to explain sleep times that differ by a factor of seven across organisms that differ in mass by six orders of magnitude," Savage and West wrote.

It also explains why elephants can thrive with just a couple hours of shut eye.