I have an actual answer, when chickens had not existed there was a creature that was super similar to the chicken, not quite a chicken then when that creature laid its egg and the egg was fertilized the egg had a mutation, which gave it a defining trait of a chicken, the egg hatched and became the first official chicken of that makes sense, basically at one point the almost chicken creatures evolved into a chicken by laying an egg and the embryos through a combination of genes and mutations became the first chicken so the egg came first, because the chicken evolved into chickens in the egg