Biology
What causes goosebumps when we don't have fur?
Quick fact
Goosebumps are caused by tiny muscles (arrector pili) contracting at the base of hair follicles, pulling hairs upright—a response that once helped our ancestors trap heat and appear larger to predators.
Why this is interesting
Goosebumps are a useless leftover from our furry past—but the reflex that causes them still fires every time you get scared or cold, even though there's no fur to stand on end.