The researchers, from the Duke University in South Carolina, believe their findings could also explain why our quality of sleep typically gets worse as we get older.

“The idea that there's a benefit to living with grandparents has been around for a while, but this study extends that idea to vigilance during nighttime sleep,” Dr David Samson, co-author of the study, told the Evening Standard.

And the researchers believe their study shows the evolutionary advantage of not getting enough sleep.

“A lot of older people go to doctors complaining that they wake up early and can’t get back to sleep,” Charlie Nunn, another co-author of the study, added.

“But maybe there’s nothing wrong with them. Maybe some of the medical issues we have today could be explained not as disorders, but as a relic of an evolutionary past in which they were beneficial.”

So next time you find yourself counting sheep in the early hours, take comfort in the fact your body probably knows what it’s doing.

Images: iStock

Insomnia is awful, but scientists have revealed the amazing reason why you have it