Where does the shape of eggs come from?

Eggs are initially soft inside of the animal and they harden due to calcium deposits only gradually over time. Thereby, the egg is constantly pressed together by the surrounding muscles. And because the egg seeks the path to the outside, it will be more pressed together at the upper side than at the bottom. Therefore, the bottom, that comes out even first, is rounder than the top.
2012-06-25 at 20:22

The egg-shaped or in the special jargon ovoid egg, has some evolutionary advantages, so that it possibly established itself on that basis. First is, of course, an advantage when laying eggs. Rounding makes it possible to lay eggs without harming. Simultaneously, the place in the eggg is at its maxium at a low surface. Although the ratio of round eggs would still be a little bit better, but then the size of the eye had also to be much larger, may be too large to lay the egg.

From this near-optimal relationship between surface and content also results that the eye does not cool down quickly (large surface area emits much temperature) and so increase the chances of survival. In addition, eggs in the form can be arranged good and near to each other in the nest, because the gaps are minimal. Also this reduces the heat loss.

Another advantage, everyone can understand when cooking or baking. Imagine, the eggs would be round. With this, rather more eggs would end up on the kitchen floor and would be destroyed. This advantage is also an advantage in the nest. Round eggs would much easier roll out of the nest, while egg-shaped eggs roll in a circle until they come to rest at some time. So, animals with egg-shaped eggs should have more survived progenies and therefore, this shape can also be prevailed.
2012-06-25 at 09:44

There are also round eggs. But as far as I know, this is only the case with soft eggs, which, with there characteristics, do not have the problem that they could not fit through the narrow passage first. Take, for example, the eggs of a fish or a frog. Frogspawn is initially quite small and pinched and then it swells in water to a perfect roundness.
2012-06-26 at 09:12