BokkChoi beat me to it.
[Edit]
For clarification:
We like to think that something came before the chicken, and its egg eventually hatched into the chicken because of evolution. We have lots of proof of this. Check out Los Galapagos Isles.
Gman went back in time , couldn't get back because he needed energy to use his time power. So he needed an egg to eat so he got it used the last of his powers to cook it but did it wrong it hatched and out came A CHICKON.