The scientific and philosophical mystery was purportedly unraveled by researchers at Sheffield and Warwick universities, according to the Daily Mail newspaper.
The scientists found that a protein found only in a chicken's ovaries is necessary for the formation of the egg, according to the paper Wednesday. The egg can therefore only exist if it has been created inside a chicken.
The protein speeds up the development of the hard shell, which is essential in protecting the delicate yolk and fluids while the chick grows inside the egg, the report 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," said Dr. Colin Freeman, from Sheffield University's Department of Engineering Materials, according to the Mail.
"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," he said."