The Threat Simulation Theory proposes that dreams evolved to allow us to practice and prepare for threatening situations.

Developed by Finnish cognitive neuroscientist Antti Revonsuo, the Threat Simulation Theory (TST) posits that the primary biological function of dreaming is to simulate threatening events and rehearse threat perception and avoidance. If our ancestors frequently faced predators or other dangers, dreaming provided a safe, virtual environment to practice responses, honing fight-or-flight mechanisms and improving survival instincts. The commonality of themes like being chased, falling, or confronting danger in dreams supports this theory. Revonsuo argues that if dreams were merely random noise, they wouldn't consistently feature such vivid and emotionally charged scenarios relevant to survival. The theory suggests that this 'training' would confer an evolutionary advantage by better preparing individuals for real-world threats, thereby increasing their chances of survival and reproduction. While not universally accepted as the sole purpose, TST provides a compelling evolutionary explanation for the prevalence of negative or challenging dream content.