Pharyngula

Bleh. MSNBC is running a terrible article that claims they have “proof” that chickens came before eggs. It’s just an awful mess, and one of the scientists is at least partly responsible.

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.

“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.

No. 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.

What were the people involved in this story thinking?