We have evolved eyelids to protect our eyes from drying out or getting scratched. When you are sleeping, it is dark anyway, so there’s not much point in your eyes being open. But your ears have evolved as an important early warning mechanism, allowing you to wake up if, say, there’s a tiger growling in the undergrowth.
Some animals, including seals, otters and hippos, can close their ears, but this is to keep water out while swimming.
Read more:
- Which evolved first: eyes or ears?
- Why do your ears pop?
- Why do our ears ring after we listen to loud music?
- Do reptiles have ears?
Subscribe to BBC Science Focus Magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.
