Why Are Eggs Egg-Shaped?

Thinkstock / Thinkstock

There’s only one thing in this world shaped like an egg. Not exactly spherical, not exactly an oval, it’s kind of hard to describe what an egg looks like. “Asymmetric tapered oval”? Sure, why not.

But why are eggs shaped this way? Evolution, my dear Watson. Evolution.

If eggs were perfectly spherical, they would be more likely to roll out of a nest and break. Instead, because they have a tapered end, they make a circular path when they roll. This path keeps them within the safe confines of their nests. Amazingly enough, birds that nest on cliffs have more oval-like eggs that roll in tighter circles. These eggs are even less likely to roll out of a nest and off of the cliff. Conversely, birds that nest on the ground lay eggs that are less oval-shaped.

The tapered shape of eggs also allows them to fit more snugly inside the nest and keep each other warm.

Additionally, eggs are tapered because an asymmetric tapered oval is the ideal shape for an egg to be pushed out of a hen. Eggs travel through the cloaca and emerge from a part of the anatomy called the vent located just under the tail, and because the tapered end of an egg has more surface area than the blunt end, the chicken’s muscles have an easier time squeezing it out. (Fun fact: A chicken's intestine is also connected to the vent, so hens relieve themselves and push out eggs via the same opening.)