The chicken, no, the egg, no, the chicken, no, the egg. It's enough to make your head spin right off your neck. We've all been through the logic; most of us end up at the same place. As Luna Lovegood, the dreamy yet dotty witch from Harry Potter put it when asked the riddle, "A circle has no beginning." And indeed, attempting to identify the first case of a circular cause and consequence is an exercise in utter futility. For those who don't have a pat story involving a divine being who spits out perfectly formed species, it's a no-win situation
Basically, many, many moons ago there was a chicken-like bird. It was genetically close to a chicken but wasn't a full-blown chicken yet. The video calls it a proto-chicken. So proto-hen laid an egg, and proto-rooster fertilized it. But when the genes from ma and pa almost-chicken fused, they combined in a new way, creating a mutation that accidentally made the baby different from its parents. Although it would take millennia for the difference to be noticed, that egg was different enough to become the official progenitor of a new species, now known as... the chicken! So in a nutshell (or an eggshell, if you like), two birds that weren't really chickens created a chicken egg, and hence, we have an answer: The egg came first, and then it hatched a chicken.