Why penguins can't fly

the long version

Many, many years ago, the relatives of today's penguins flew over the ocean and dove down into the water for food. As time went on, flying became unnecessary for their survival. They didn't have any enemies on land that would necessitate escape by air. Penguins spent most of their time in water; air wings gave way to flipper-like water wings. This change made penguins able to fly through water, using the same motions that other birds used to fly through the air. This is a fictional story about why penguins can't fly today.