Here’s a question that someone raised with me – did our ancestors sleep longer in winter? He said he’d been told that our bodies are not meant to sleep for the full winter night, that in Tudor times people would get up in the middle of the night and do their accounts or some housework then have another ‘little sleep’.
This makes no sense to me. Being in bed keeps you warm, so no need for fires. Cold weather wears you out maintaining your body temperature, so a long time in bed makes sense.
Closer to home, I once shared a house with a woman from Iceland and she definitely slept a lot more in winter and drove us mad with her early rising and late nights in summer.