To add to this developing theory:-
Some years ago, one of my daughters had a DNA test at uni for an ancestral
trait.
Turns out to have been of viking origin, so wife and self followed suit.
As I had worked extensively in the Baltic and loved every moment, I assumed
it was my genes, and felt quite privileged.
Not so it transpired, it was 'er indoors to her great delight.
My wife can sleep under 2 x 15 tog duvets at any time and loves 30C+ temps.
I dispense with 5 tog duvets over 15C and a hot day commences at 20C.
Need less to say, we have separate sleeping arrangements!
Peter J