I am mtdna haplogroup J, and it is said we produce more body heat (as a favorable adaptation to northern climes) than the others-in fact, this is why I had predicted my mtdna to be J before I took the 23andMe test (despite it being a minority of about 11% where my maternal line comes from), and was not surprised when I found out I was J1c2b. To me, 'Winter is Coming' is less a pronouncement of doom than a, to paraphrase Ben Franklin in his quote about beer, proof that God loves us and wants us to be happy. This is despite the fact that I have an artificial heart valve (aorta) and take a blood thinner, which with most people makes them cold. My brother is similarly heat intolerant, but not our sister, which I chalk up to differences in body type; my brother and I are both broad chested and thick hipped while our sister is not.