Biologically, the egg must have come first because the gentic structure of an organism does not change throughout the course of the organism's life. Couldn't be bothered to explain it all, but it comes down to the fact each generation produces minor mutations, as per Darwin's theory of evolution, minutely altering the genetic makeup of the chicken. Eventuually an egg was produced, with the dna/genes ect of the chicken, which was slightly different to the parents, because of both the combination of sex cells and natural mutations.
Yeah, over the top, whatever
Just answered the fucking question