Scientist: We Have Proof That The Chicken Came Before The Egg

"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," says Dr. Colin Freeman, from Sheffield University. Here's the explanation.

When scientists from Sheffield University and Warwick University used a supercomputer called HECToR to take a close look at egg shells, they discovered that a protein "called ovocledidin-17 (OC-17) acts as a catalyst to speed up the development of the shell." They realized that this protein is crucial to actually forming an egg shell. They also realized that this protein is found in a chicken's ovaries. Based on this, these scientists decided that the chicken must have come before the egg.

What they found was a specific molecule called ovocleidin which is a member of a family of C-type lectin-like proteins. These things are all over the place; they're cell adhesion molecules, some are involved in cell signaling, some function in modulating the immune system and blood clotting pathways. They're even found in snake venoms. They're found in everything from C. elegans to mammals. Their key property is that they bind calcium.

In birds, these proteins have been coopted to regulate egg shell formation. They bind calcium and can seed the crystallization of calcium carbonate, and also control the rate of crystal formation. Chickens have ovocleidin, but geese have an ortholog, ansocalcin, and ostriches have struthiocleidin. There seems to be a lot of lability in what particular calcium-binding protein is used in shell formation, and it's probably the case that most of the sequence is free to mutate without affecting the nucleating function.

You simply can't make the conclusion the reporter was making here. The species ancestral to Gallus gallus laid eggs, the last common ancestor of all birds laid eggs, the reptiles that preceded the birds laid eggs…the appearance of egg laying was not coincident with the evolution of ovocleidin. The first chicken that acquired the protein we call ovocleidin now by mutation of a prior protein also hatched from an egg.