The egg, egg cells have been around for millions of years.
If you meant "chicken or chicken egg" then the egg, layed by a species that was not at that point classified as a chicken, but an extremely closely related 'transition species', most likely a subspecies of something else.
Thing is, humans with scientfific taxonomy werent around back then to actually witness the evolution of the chicken, but that's probably how it would have gone if we were, probably using DNA sequenses to determine the transition species.
Lol.