One of nature's most efficient life-support systems is the egg. Eggs evolved over 300 million years ago as vertebrate animals adapted to living on land. And since then, they've taken on numerous shapes, especially among birds.
Biologists have long wondered why there are so many shapes, and what determines each one. Hummingbirds, for example, have eggs like Tic Tacs. Birds called murres produce eggs shaped like big teardrops. Some eggs are more like pingpong balls.
Now, an international team of scientists believes it has solved the mystery of the eggs.