I guess it is quite logical that the "chicken" was first. First live forms to be were reproducing themselves by dividing their cells. Once they evolved into more complicated beings, they begun to adapt more sophisticated ways to reproduce, depending on the conditions they lived in and how they were living (i.e. on trees or in the water). All those changes took place over many generations, of course, but it practically means that first there was a "chicken", and then it begun to lay eggs.
Correct me if I am wrong.
