Some scientists seem to believe the egg evolved first but the best explanation I can find is from Richard Dawkins (famous scientist) who didn’t come up with an definitive answer. Basically he says that every animal has got to have parents and all animals will be recognisable from the generation before them but not from generations thousands of years apart. His point is that the chicken evolved very slowly over time and it is very difficult to pin down exactly when it became a chicken or an egg for that matter ? ?. It is confusing (I’m confused!!) but I hope this helps
My argument is very close to Karens, but could also be totally wrong.
Imagine you have a creature which looks like a chicken, and acts like a chicken, but it doesn’t make the right clucking noise that a chicken does. Instead, it moo’s. I’m going to call this creature a “proto-chicken”.
When the “proto-chicken” lays an egg, evolution decides that the baby is instead going to cluck, because clucking is a better noise. And so, when the egg hatches, you get your first chicken. So egg came first (kind of).
Evolution (of course) isn’t as simple as this. As Karen said, each generation of “proto-chicken” is only slightly different to the one that came before (each chick is like it’s mom, but just slightly different). But a chick is very, very different from its great-great-great-great-great-great-great-grandmother, because lots of changes happened over those generations.