We know for sure the egg came first. The first true chicken hatched from an egg laid by a bird that was not quite a chicken. This is a classic example of anagenesis, where a single lineage changes gradually over time without a sharp break. Evolution works by tiny steps, not sudden leaps, so at some fuzzy boundary, a non-chicken laid an egg containing the final traits we now call “chicken.” That egg came first. Birds evolved from reptiles millions of years ago, while chicken-like animals appeared only about 58,000 years ago, with our modern domestic chicken emerging roughly 8,000 years ago.