Scientists say every animal needs sleep. These fruit flies didn’t get the memo

Ask parents of newborns whether they think sleep is overrated and you’re liable to catch a death stare. Yet some fruit flies almost never nod off, according to a new study, suggesting that at least in some animals, sleep may not be all that necessary.

Sleep is potentially costly to many animals, making them vulnerable to predators and stealing time from resource-gathering or mating opportunities. For that reason, scientists have long assumed it evolved to give animals some vital, evolutionary advantage—perhaps as a means of conserving energy or of giving the brain time to organize memories. In any case, no truly sleepless animal has ever been found in the wild.

In the new study, researchers were observing Drosophila melanogaster fruit flies in the lab when they noticed a very large distribution in sleep duration. Most slept somewhere between 300 minutes and 600 minutes per day, but about 6% of females slept for less than 72 minutes per day, and three particularly restless individuals slept for only 15, 14, or 4 minutes per day, respectively.

This lack of sleep seemed to have no ill effects on health. Sleepless flies lived just as long as other flies, the researchers report today in Science Advances , and even flies with typical sleep schedules weren’t bothered when housed inside a rotating tube that forced them to lose about 96% of their sleep time.

The authors say their findings undercut the common wisdom that sleep plays an indispensable biological role. Instead, they say, we should adopt the view that sleep probably does serve some as-yet-unknown evolutionary purpose, but it isn’t strictly necessary. Just don’t tell that to new parents.