My theory (similar to what owl said) Is the egg.
Because
The egg must have came from an evolution animal. specifically dinosaurs. It started to evolve to turn into the chickens w eknow today. The first chicken in evolution had to come from an egg given birth to by an animal in evolution. More specifically as mentioned before, a dinosaur. The chicken came after the egg. So the answer in my opinion is.......
The egg came first!
Okay, but really...
The came first—
The egg, obviously.
