A sound night’s sleep grows more elusive as people get older, but what some call insomnia may actually be an age-old survival mechanism.

Trouble sleeping is a common complaint among older folks, but what if their insomnia traces back to prehistoric times when Grandma and Grandpa were in charge of keeping the cave safe at night?

If your sleep is getting worse with age, evolution might be to blame. A study recently published in Proceedings of the Royal Society B found that humans' age-specific sleep patterns may have evolved to protect mixed-age groups from potential danger in the night. And in this scenario, the elderly members of these groups may have drawn the short straw—their restless sleep made them perfect for the night watch.

You may not look forward to sleeping less as you get older. But maybe it wouldn’t seem as bad if you knew it once played an important role in human survival.

Poor sleep is often regarded as a modern affliction linked to our sedentary lifestyles, electric lighting and smartphones on the bedside table.