Asked by: Zvi Albert, Manchester
If you trace the family tree of any chicken back through its ancestors, you will find that each one hatched from an egg that was in turn laid by a chicken and so on. But if you go back over 10,000 years, you eventually reach the wild ancestors of the domestic chicken, which were probably the red and grey jungle fowls of Southeast Asia.
You could draw a line there and say all ancestors prior to that were not chickens, but everything from that point on was. Whatever attributes qualified this individual to be a chicken, they were set at the moment the egg and sperm met. I would argue this means the egg came first.
This argument does depend on the acceptance of modern theories of evolution and genetics. A Lamarckian view of evolution (in which animals could pass on physical characteristics acquired in their lifetimes) would imply that a non-chicken could evolve into a chicken within its own lifetime and thus the chicken would have come first.