Chicken and Egg

Which came first, the chicken or the egg?

Sometime ago, someone commented that a certain issue was like the chicken and egg issue. Like, which came first?

Which started me thinking. Was it really like the chicken and egg issue?

Say you are answering the question from a creationist perspective. Your answer is quite direct, that the chicken came first. Cause God created the animals. And thats about it. There is not much issue about it.

If not creationist, lets say you are answering from a naturalist / intelligent design / evolutionist / materialist / evolutionist point of view. According to this view, the chicken emerged from the reptiles (I think) or some other animal. In that case, isn't the only proper answer to the question be another: What is a chicken?

If one gradually changes to another, then how would you know when the animal stops being a reptile and starts being a chicken? And if you do not know what a chicken is, then how would you know whether it starts being a chicken from its genes or from its genes mutation (that is, from the time it is an egg or from a time in its life)

So, what is a chicken?