The egg came first because chickens, as a species,became chickens through a long, slow process known as evolution. At some point, a chicken like bird produced an offspring that,due to some mutation in its DNA,crossed the threshold from mere chicken into chicken actuality. A proto-chicken gave birth to a real-life chicken and since that real-life official chicken came out of its own egg, we can say that the egg came first.
Source Flickr/ From prairie m
Source Popular Science