Why Are Bird Eggs Egg-Shaped? An Eggsplainer

Ed Yong in The Atlantic:

When Mary Caswell Stoddard started measuring bird eggs from hundreds of species, she wasn’t expecting to learn that most eggs are not egg-shaped.

Think about an egg and you’ll probably conjure up an ellipse that’s slightly fatter at one end—the classic chicken egg. But chickens are outliers. Hummingbirds lay eggs that look like Tic Tacs, owls lay nigh-perfect spheres, and sandpipers lay almost conical eggs that end in a rounded point. After analyzing hundreds of species, Stoddard showed that the most common shape—exemplified by an unremarkable songbird called the graceful prinia—is more pointed than a chicken’s.

“We mapped egg shapes like astronomers map stars,” Stoddard says. “And our concept of an egg is on the periphery of egg shapes.”

Beyond displacing chickens as the Platonic ideal of egg-dom, Stoddard’s data also helped her to solve a mystery that scientists have debated for centuries: Why exactly are eggs shaped the way they are?

More here.