Why can't penguins fly?

Sure, penguins can have happy feet. But why don't they have happy wings?

It turns out that birds can be good at flying, or good at swimming, but they probably can't be good at both.

Researchers recently looked at birds like the cormorant and the murre that are okay at diving and at swimming, but not great at both. It  turns out they expend more energy than the average bird when they fly - and a lot more energy than a penguin when they dive. So the researchers believe that penguins are uniquely adapted to fast swimming using minimal energy - and that means they'll never be good at flying.

Read more at Nature: http://goo.gl/ZLgL3

(Image: Stan Shebs http://goo.gl/iiKHf from Wikipedia http://goo.gl/zI2eQ)
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