Yes, it’s the egg. It has actually been definitely answered for almost 20 years that Wikipedia has a section on this

By most every definition of the dilemma it will be the egg which came first. The very first “egg” in our world came long before birds are a thing. If we are strictly talking about chicken eggs, since the modern chicken is a domesticated animal, strictly speaking the first true domesticated chicken came from two non-domestic chicken parents… which created a fertilized egg that became the first domesticated chicken.