Book 33, Question 2
Why do all mammals have three tiny bones in each ear?
Inside your ear are three bones called the hammer, anvil, and stirrup.
They are the smallest bones in your body. When sound hits your eardrum, the bones pass the shaking along to the inner ear. Millions of years ago, the ancestors of mammals used some of these same bones in their jaws. Over time, they became tiny helpers for hearing.