... it depends on semantics. Just as a sort of gedankenexperiment (thought experiment), allow me to take this one on. Deep breath...
The first step involves the need to be really clear about what we mean when we say “a chicken”. You could start this by collecting a sample of birds, say a hundred or so, male and female, that you’re happy to call healthy, modern chickens. You put them all in your chicken shack (you’re going to need a very big shack for this).
Then you invent some sort of super genetic compatibility tester that can scan an individual bird’s genome and test for potential reproductive compatibility with all the chickens in your shack that are of opposite sex to the one under test. If your bird can successfully make fertile offspring with these, your tester flashes green.
Now you scour the world, testing every candidate for chickenhood in existence. Green light – the tested bird meets your definition of a chicken and goes into your shack. Red light – it’s not a chicken.
Next step involves building a time machine. If you travel back a few hundred million years, you won’t find a candidate for your chicken tester anywhere in the world. In fact, you won’t find any birds at all. Fast forward to about 100 million years ago and there are plenty of birds about, but it’s highly unlikely that any of them will pass your test with a green light. Your modern chickens will be just too genetically dissimilar to them. But some point further on from there, you’ll find your first candidates and start testing them. And you travel forward through time, testing every single candidate for chickenhood that has ever lived. Only the green lighters go in the shack. Naturally, these get more numerous as you approach our present time.
At the end of this process, you will have a shack that contains every chicken that has ever lived and met your criteria. The whole point of this, of course, is to show that it’s possible to consider as a mathematical set “every chicken ever”.
Now it has to be the case that one bird in your shack qualifies as the first ever chicken (you could say that you’re going to decide that using perfect data about, for example, the precise instant your chicken cracked its eggshell). This one bird was born to parents who are both NOT in your shack (they red lighted on the test). If you go and find them, they will most likely look like chickens to you. They will squawk like a chicken. If you slaughter them and eat them – hey, tastes like chicken! But they’re not chickens. They failed your test.
Now, we only need to define what we mean by the egg in the question. It has to be a chicken egg, right? As has been said, there are millions of other eggs about which it would just not make sense to enquire. But what do we mean by a chicken egg? Any egg laid by a chicken? Or an egg from which a chicken can hatch?
If you opt for the former, then the chicken came before the egg. “The egg” in this case was either laid by our first chicken (if it’s female) or by the first female in your collection to lay an egg (if your first chicken happens to be male). If you opt for the latter definition, then the egg came before the chicken, and was laid by the non-chicken mother of your first born chicken.
So, there are the possible answers. The choice I'll leave with you.
