Goosebumps and Chills Have an Evolutionary Purpose
Chills happen when tiny muscles around the base of each hair follicle tense and erect the body hair. Thousands of years ago, human hair was a lot thicker, kind of like fur. And getting the chills would fluff up the fur, giving the body more insulation.
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As for goosebumps, they’re more of a defense mechanism. It’s a process similar to how mammals bulk up their fur when threatened so that they look bigger and more intimidating to their predators.