Whose research first helped explain that mammalian fur is an adaptation for insulation and sensing the environment?

Fur is one of the defining features of mammals, and its functions were established gradually through comparative biology. Scientists showed that fur helps regulate body temperature, protect the skin, and in some mammals assist touch and sensing through specialized whiskers. The study of fur and hair also became important in evolution and taxonomy. Mammalian pelage is now understood as a multifunctional adaptation rather than just a coat.