What You Can Learn From Hunter-Gatherers' Sleeping Patterns

"...The Hadza, Tsimane, and San were also strongly affected by falling temperature, much more so than failing light. They start to sleep as the night cools and begin waking up at its coldest point. “This suggests that temperature is a very strong and evolutionarily old signal that gets integrated into sleep-regulating systems in the brain, and that we could exploit better,” says van Someren. And as Siegel adds, “This temperature rhythm has been reduced or completely eliminated for most of us by our shelters and heating systems.”"

https://www.theatlantic.com/science/archive/2015/10/the-many-myths-of-paleo-sleeping/410707/

It's not what you think.