How Do Eggs Get Their Shapes? Scientists Think They've Cracked It

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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.

Biologist Mary Caswell Stoddard of Princeton University led the team. She had heard the shape theories: Cone-shape eggs don't roll away, they roll in a tight circle so maybe that's good for birds that nest on cliffs. Or elliptical eggs, like slightly flattened spheres, might stack closer in nests and incubate better.

Stoddard looked at nearly 50,000 eggs and cross-checked them with 1,400 bird species. "We are able to look at the egg in many dimensions and crack the mystery," she says.