A team made up of a geneticist, philosopher and chicken farmer claim to have found an answer. It was the egg.
Put simply, the reason is down to the fact that genetic material does not change during an animal's life.
Therefore the first bird that evolved into what we would call a chicken, probably in prehistoric times, must have first existed as an embryo inside an egg.
Professor John Brookfield, a specialist in evolutionary genetics at the University of Nottingham, told the UK Press Association the pecking order was clear.
The living organism inside the eggshell would have had the same DNA as the chicken it would develop into, he said.
"Therefore, the first living thing which we could say unequivocally was a member of the species would be this first egg," he added. "So, I would conclude that the egg came first."
The same conclusion was reached by his fellow "eggsperts" Professor David Papineau, of King's College London, and poultry farmer Charles Bourns.
Mr Papineau, an expert in the philosophy of science, agreed that the first chicken came from an egg and that proves there were chicken eggs before chickens.
He told PA people were mistaken if they argued that the mutant egg belonged to the "non-chicken" bird parents.
"I would argue it is a chicken egg if it has a chicken in it," he said.
"If a kangaroo laid an egg from which an ostrich hatched, that would surely be an ostrich egg, not a kangaroo egg."
Bourns, chairman of trade body Great British Chicken, said he was also firmly in the pro-egg camp.
He said: "Eggs were around long before the first chicken arrived. Of course, they may not have been chicken eggs as we see them today, but they were eggs."
The debate, which may come as a relief to those with argumentative relatives, was organized by Disney to promote the release of the film "Chicken Little" on DVD.