[Tserisa]

The animal that chickens are domesticated from did not lay a bunch of fertilized eggs. If they did not mate, they did not lay eggs.

Very few wild birds will lay an unfertilized egg. It is a terrible strain on their physical resources, attractant to predators, and can even be deadly (constantly forming eggs causes calcium deficiencies and conditions like egg-binding). So, for evolutionary and biological reasons, birds do not just lay eggs willy-nilly.

Sometimes captive wild birds will do so in strange situations (i.e. if they are stimulated to do so by a combination of diet, lighting, housing, etc.) but with wild type birds (large parrots, etc.) it is uncommon. However, in domesticated bird species -- such as fowl, cockatiels and the like -- humans have complicated matters for them so that some will start laying eggs more easily when stimulated.

Chickens, however, have been purposefully bred to lay eggs constantly. They started keeping chickens, and breeding the ones that were more likely to lay eggs when stimulated, etc. etc. until eventually the chickens were laying eggs constantly.

It is not a natural process, it is manufactured.