Goosebumps served as a vital survival tool for our hairy ancestors to trap heat and scare off predators.

Millions of years ago, our ancestors were covered in thick hair. When they got cold, goosebumps fluffed up their fur to trap a warm layer of air next to their skin. It worked just like a cozy winter jacket. If a wild animal threatened them, the standing hair made them look much bigger and scarier to attackers. Today, we still have the same reaction, even though we no longer have the thick fur to make it useful.