I solved that one way back. Solution's obvious when you look at it closely. Here's how:-
Just keep asking the question over and over ... take an egg, any chicken egg, and ask what came before it? obvious: a chicken. Now consider THAT chicken, and ask what came before it? obvious: an egg. Now consider THAT egg ... etc. Don't stop. Keep going. On, and on, way back, through time and history.
You go back up the chain of evolution.
To the predecessor of chickens, that ran around on land
to amphibians
to reptiles
to fish
to protozoa
to ...
until you come up with simple single-cellular organisms that reproduce by CELL DIVISION, creating an IDENTICAL COPY OF THEMSELVES not by creating an embryonic form or immature form.
And that's the answer.
What came first is the "chickenegg", i.e. a creature that is so simple it is both the chicken AND the egg.
QED
Of course if you're a creationist, the answer's even simpler.