In these days of uniform food production, hens are sticking with an asymmetrical, tapered oval shape for good reasons. It certainly isn’t because they fit nicely into the container in your fridge!
Box shaped eggs will be very strong at the corners, but weak in the middle of the walls. And they’d be really tough to lay! Eggs are laid with the blunt end coming out first, followed by the tapered end. The tapered end has the ideal shape for the hen’s muscles to push on. You can imagine the difference if you think about squeezing a tapered cherry pit between your fingers and squirting it some distance, compared with trying to project a cube of sugar by squeezing it between your fingers.
Although a spherical shape is the strongest shape of all, completely round eggs would easily roll away down a hill and be lost. Eggs with the asymmetrical, tapered shape roll back to you if you nudge them, moving in a circle around a pointed end. It’s interesting that eggs of cliff dwelling birds are generally more oval than birds that nest on the ground. They roll in a very tight circle, and are less likely to roll off the cliff.
Another advantage of the egg shape is that eggs pack together nicely in the nest with only small air spaces between them. This means that more eggs fit into the nest and they help keep each other warm while hatching.
So next time you crack an egg, marvel at it’s ideal shape.