Hi I dontknowagoodname.
I believe it stemmed from the fact that food was something that one had to find or slay to survive. As a result, every part of the animal was put to use. By maximising the potential of a carcass, native man probably didnt have to go hunting for food so often. Every tried slaying a mammoth?
Anyway, in drying hides, one possibly stumbled upon the ability to also use that hide to increase warmth, and then in all probability it followed from there much like the same as all things have developed. An initial concept, that is then built on continually.
Shaz