Researchers at the University of Sheffield and Warwick found that a protein called ovocleidin-17 (OC-17) is essential for forming eggshells, and it's produced only inside a hen’s ovaries. This discovery strongly supports the idea that the chicken had to exist before the egg could be formed.

The protein acts as a catalyst, helping calcium carbonate crystallize into shell structure—something only a chicken’s body can do. So, based on this science, the age-old debate finally has a clear answer: the chicken came first.