The egg came before the chicken, now what the hell is a pre-chicken?

Okay, the egg came before the chicken, and here's why: What we define as a chicken came about through a gradual series of mutations from some other animal. There is a threshold that separates what we call a chicken from its ancestor. One genetic mutation between chicken, and not chicken. That mutation occurs at conception, and so the egg contains the mutated animal that is a chicken, laid by it's non-mutated parent, not a chicken. QED.

Now that we have an answer for that, we can finally move on to other questions about existence, like what should we call the strange monster that came before the egg (Pre-chicken)? And how is that related to what McDonald's used to make McNuggets out of before they switched to 100% real chicken?