Goosebumps are actually a useless holdover from our hairier days and we get them in reaction to the cold, to fear or any other strong emotion.
What happens is, when we walk into a freezer or suddenly find ourselves face-to-face with a grizzly, the part of our brain called the hypothalamus kicks in.
It signals our body to produce adrenaline, which then causes muscles at the base of our hairs to contract and stand on end.
We're not exactly covered in a dense coat of hair these days . . . well, at least not most of us . . . so all we see are raised bumps.
But back in the good old days, those raised hairs allowed us to trap a layer of air, insulating us from the cold, and this hair-raising reaction also had the benefit of making us look bigger to predators, which gave us a fraction of time to either run or 'bring it.'
Well, I'll be a monkey's uncle! Er, distant relative . . . whatever.