The main problem is that at the beginning there was absolutely no difference between chicken and egg. The bacterium suddently divided itself into two equal bacteria, so you couldn't even tell which of both was the "mother".
So, looking at the problem from this pov, the answer is: BOTH.
However, the question is about chicken and egg. Noone said the egg had to contain a future chicken, so on the other hand the egg was absolutely first.
PS: I haven't read the last posts, I just thought about the problem a while and got to other answers 
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