My understanding is that REM isn't particularly deep. Quick web searches aren't actually defining it as more like light or deep sleep, but many of our systems a

My understanding is that REM isn't particularly deep. Quick web searches aren't actually defining it as more like light or deep sleep, but many of our systems are more active than other stages[1][2]. Still I don't think it's super surprising that we spend more time in REM since our brains are uniquely complex and we spend a lot of energy on perception and interpretation, which REM seems to help with [1][3]. And I would be willing to be safety and comfort also play a decent role in it as well! 1: https://www.healthline.com/health/how-much-deep-sleep-do-you-need#waking-up-tired https://www.healthline.com/health/how-much-deep-sleep-do-you... 2: https://www.health.harvard.edu/healthy-aging-and-longevity/rem-sleep-what-is-it-why-is-it-important-and-how-can-you-get-more-of-it https://www.health.harvard.edu/healthy-aging-and-longevity/r... 3: https://www.sleepfoundation.org/stages-of-sleep/rem-sleep https://www.sleepfoundation.org/stages-of-sleep/rem-sleep