The egg came first.
You know, first there were dinosaurs wich layed eggs. Some million years and evolutions later a chicken came out of an egg.
The egg.
Somewhere along the lines there was some genetic mutation which caused the chicken to be 'born' from the egg. The egg is where the genetic mutation would've taken place. I don't think a chicken would just start laying eggs someday. Chickens would've come from eggs.