By Rebecca MorelleScience reporter, BBC World Service

In the water, penguins can swim with agility and ease – but this ability might have cost these creatures the power of flight

The puzzle of why the penguin is unable to fly may have finally been solved.

Researchers believe that the bird’s underwater prowess may have cost it its ability to fly.

By looking at seabirds closely related to the penguin, scientists confirmed that a wing that is good for flying cannot also be good for diving and swimming.

The study is published in the Proceedings of the National Academy of Sciences.

Professor John Speakman, from the University of Aberdeen and the Chinese Academy of Sciences, said: “Like many people, I’ve always been interested in penguins, and seeing them do these phenomenal marches across the ice, I’ve often thought: ‘Why don’t they just fly?’

“And it’s really great to be involved in the group of people that have solved it.”

Stubby wings