At one point, we were all pretty hairy. Completely hairy. While most of us have lost the bulk of our body hair, the internal wiring is still present, as evidenced by goosebumps. (or goosepimples as I’ve heard some folks say)
Goosebumps are an automatic reaction of the nervous system that flexes the piloerector muscle found at every hair follicle. Piloerector literally means making the hair stand on end. This reaction is caused by one of two things… either you are cold, or you are scared.
Looking at cats, or anything else more furry than us, they can puff up their fur when it’s cold to trap and hold more air around thier body, thus insulating and staying warmer. Our goosebumps are trying to do the same thing.
As for being scared, the fur puffing reaction is seen in many animals as an attempt to make themselves appear larger and more threatening than they are. Again, without fur, it ain’t so scary… unless you fear chicken skin.
Today the only benefit of chest hair is that it keeps your chilly gold medallion from directly contacting your skin.