BBC Earth Unplugged - Zoo La La - Why are eggs shaped like eggs?
http://www.youtube.com/watch?v=D4nDoi7qxb8
Hello and welcome to Zoo La La, we’re here in the belly of Bristol City museum to ask the question. Why are eggs so, well, egg-shaped? At just over a centimeter, this hummingbird egg is one of the smallest in the world. But weighting in, at their modest, 1.5 kilograms, the ostrich egg is the largest.
So there’s something with this eggy shape that makes it a winning formula, but what is it? There are a number of different theories. Theory number one, it’s about keeping warm. That eggy shape allows them to fit tightly together in the nest, minimizing the egg gap in-between.
Several ground-nesting birds lay their eggs like mini-pyramid with a sharp point at the end. This allows 3 to 4 eggs to fit snuggly together in the nest, so that mom can keep them warm more efficiently.
So why else would a bird want to lay an egg-shaped egg? Theory number two, it’s all about safety. Eggs are often laid in a precarious location, and one small knock can send them tumbling to the ground. But that special egg shape means they tend to roll around the inside of the nest, rather than fall off the edge. Many cleft-nesting birds have taken this to the extreme. Razorbill and Guillemot lays extremely conical shape eggs, meaning they roll in a very tight circle, keeping them on the cleft, and not in the sea. In contrast, many birds who nest in burrows or cavities lay more spherical-shaped eggs. Like this Tony Owl egg, laid in the tree hollow, there’s little chance it’s going to roll into the path of danger, so not all eggs are egg-shaped. Extremely small birds like the hummingbirds lay elongated eggs. These small birds have such a tiny pelvis; they simply couldn’t lay a large round egg. Yet there has to be enough substance inside the egg to ensure the survival of the embryo, so they simply lay a long narrow egg.
Theory number three, might come of a little bit of surprise. It all about strength, egg has no sharp edges, which mean they can withstand more force that you might imagine. Most structure break at the corners and edges, these points concentrated the force to one area and this can leads to disaster. It’s the same reason of a piece of paper is relatively easy to tear apart when there’s a rip already in it. The force is concentrated around the tear, making it really easy to rip apart. On the other hand, if any forces placed on an egg, it’s evenly distributed across the whole surface. There is no one area for it to concentrate. In fact the shape is so strong that this egg should remain intact if I squeeze it equally from every direction. That’s amazing, it actually won’t break. If pressure is apply equally from all sides, even the world strongest man couldn’t break it.
The shape simply disperses the force evenly across the shell, and it gets better. Although this shape can withstand a lot of compression, it’s actually really weak in the opposite direction, so the chicks inside can break free.
So for whatever reason eggs are egg-shaped, we should be grateful because they fits so perfectly into our egg cups. If you have any weird animal questions, then type them into the comment box below. See you next time on Zoo-La-La!
