This is one of those questions that has been circulated around for many years, even I can remember debating it at school many years ago.
According to Genesis, the chicken came first, but scientists over at National Geographic magazine have been considering this thorny old question and have come down firmly on the side of the egg.
Apparently, reptiles were laying eggs thousands of years before chickens ever appeared. So a long time ago, an egg that was not quite a chicken’s egg was laid by a bird that was not quite a chicken. Evolution took it from there.
What’s your theory?