It's the age-old question that has puzzled the finest minds for thousands of years - which came first: The chicken or the egg?
Now, scientists claim to have finally discovered the answer to the conundrum - it's the chicken which came first.
A team from University of Sheffield and University of Warwick has found that a protein called ovocleidin (OC-17) is crucial in the formation of eggshells.
It is produced in the pregnant hen's ovaries so the correct reply to the egg riddle must be that the chicken came first, the scientists say.
However, the research does not come up with how the protein-producing chicken existed in the first place, the 'Daily Express' reported.
The team used a hi-tech computer, called HECToR, to look at the molecular structure of a shell.
They discovered that OC-17 acts as a catalyst, kick-starting the conversion of calcium carbonate in the chicken's body into calcite crystals.
It is these that make up the hard shell that houses the yolk and its protective fluids while the chick develops.
Lead scientist Dr Colin Freeman of Sheffield University said: "It had long been suspected that the egg came first but now we have the scientific proof that shows that in fact the chicken came first.
"The protein had been identified before and it was linked to egg formation but by examining it closely we have been able to see how it controls the process. It's very interesting to find that different types of avian species seem to have a variation of the protein that does the same job."
The scientists now hope the breakthrough could be used in industry to help develop new materials.
Team member Prof John Harding said: "Nature has found innovative solutions that work for all kinds of problems in materials science and technology. We learn a lot from them."
Calcite crystals are found in numerous bones and shells but chickens form them quicker than any other species, creating six grams (0.2oz) of shell every 24 hours. Once the shell has formed, the chicken expels the egg.