The muscles that make hair stand up, known as arrector pili muscles, are considered vestigial in humans because they serve little practical purpose in modern life. These small muscles are attached to hair follicles and contract when you’re cold or scared, causing the phenomenon known as “goosebumps.”
In our ancestors, this reaction helped trap heat by fluffing up body hair to create insulation or made them appear larger to predators. However, since humans now have minimal body hair compared to our evolutionary predecessors, this function is largely redundant. With clothing and other means to regulate body temperature, the arrector pili muscles remain a fascinating but unnecessary evolutionary remnant.
