The question, while witty, is too vague. "Chicken" brings up some difficulties, most notably, what would distinguish the earliest chickens from their evolutionary predecessor? Evolution is generally a slow process - very slow, occurring over tens of thousands of years at the swiftest pace. In any case, I'd argue egg - if the chicken is (genetically) indistinguishable at it's earliest stages from the evolutionary predecessor, you probably would not announce that the chicken species has really emerged.