Necroseer a dit :

That's what I originally thought but apparently there's a protein in chicken eggs which only chickens themselves can produce. This means that the chicken came before the chicken egg. There was a thread on this on the old forums and this seemed to be the general concensus, and there was a link to an article about this protein. I'll try to dig around for it.

Edit: "Scientists cracked the puzzle after discovering that the formation of eggs is possible only thanks to a protein found in chicken's ovaries. That means eggs have to be formed in chickens first."

Read more: http://www.foxnews.com/scitech/2010/07/14/chicken-egg-mystery-finally-cracked/#ixzz228BFW5Qf