Why Do Humans Have Nightmares? An Evolutionary Biologist Explains

InnovationScienceWhy Do Humans Have Nightmares? An Evolutionary Biologist ExplainsByScott Travers,Contributor.Forbes contributors publish independent expert analyses and insights. I write about biodiversity and the hidden quirks of the natural world.Follow AuthorMay 12, 2026, 08:30am EDT--:-- / --:--This voice experience is generated by AI. Learn more.This voice experience is generated by AI. Learn more.The nightmare that jolts you awake at 3 a.m. isn’t a malfunction. It may be one of the oldest survival systems in the human brain.gettyYou’re being chased. Something is behind you — you can’t see it clearly, but you know, with the particular certainty that only dreams afford, that it means to harm you. You try to scream. Nothing comes out. You try to run. Your legs are concrete. Then you wake up. Your heart is hammering, your sheets are damp, and the darkness of your bedroom slowly reassembles itself into something familiar and safe. You’ve just had a nightmare. So has virtually every other human being alive.The ancient Mesopotamians wrote about them on clay tablets. Aristotle puzzled over them in On Dreams. For most of human history, we’ve treated nightmares as visitations, omens, punishments and the work of malevolent spirits pressing down on sleeping chests. What we’ve rarely considered is a far stranger possibility: that the nightmare isn’t a malfunction. In fact, it’s probably a system working exactly as designed.Evolutionary biologists are increasingly making that case. And the evidence, drawn from neuroscience, genetics and cross-cultural psychology, is difficult to dismiss.Nightmares Might Be The Brain’s Oldest Flight SimulatorIn 2000, neuroscientist Antti Revonsuo published a paper in Behavioral and Brain Sciences that reframed how scientists think about dreaming. His argument, which he called Threat Simulation Theory, was deceptively simple: the biological function of dreaming is to simulate threatening events and rehearse the behaviors needed to survive th...