Granted I don't have any sort of a time machine and it may well be that God simply created humans without fur coats.
Nonetheless IF humans originally had fur coats and subsequently lost them, and particularly if they lost them via any sort of a process which you might describe as microevolution, then none of the explanations or attempted explanations for it which I've ever seen really work.
Best attempts I've seen are those of Elaine Morgan and Danny Vendramini but I still could not recommend either for various reasons, and neither really provides any idea of an ADVANTAGE which losing fur coats might have conferred.
But just from my own studies, I've come up with one really big advantage which losing a fur coat would confer, assuming you didn't freeze to death in the process i.e. before you learned to manufacture clothing.
What I'm talking about here is handling fire. Picture some poor homo erectite or Neanderthal eating a piece of raw meat on some hunting trip and thinking to himself:
"Man I wish I could cook this stuff and I would if I were safely back in my cafe without all this damned WIND, but NO WAY am I gonna risk catching my own butt and myown 6" fur coat on fire...
THAT would be the one really big edge to losing the fur coat and naturally you'd only ever see it on a creature which handled fire.