Well my first thought would be egg, but then who laid the egg? If it was a chicken where did the chicken hatch from? However if we look back chickens have not been on earth from the start so most likely the egg did come first, but that egg had a mother that was very close to the chicken that hatched from the egg, but that mother most likely came from an egg herself. ♥ In short if you put some thought into it it seems the egg is most likely. ♥ So I would have to say egg. ♥
I'd choose Chicken for this one. There is this one theory about dinosaurs stating that the reason why they are humongous compared to the height of the lizards nowadays is because they lived in Earth's period wherein there was a low oxygen percentage in the planet. Because of that, there is an occurrence of animal gigantism. In the world we live in today, we have an oxygen percentage of around 20 - 30 percent, which caused us (and the lizards) to shrink to our size today. Pairing this theory with another one stating that the animal kingdom was formed through bacteria (or something, I don't really remember) and took shape for a hundred or so million years, it is possible that chicken are formed first and laid eggs. Though there is also the statement about eggs coming first with the reason of proto-birds thingy mated (two different breeds) and out came a chicken, which I really do not believe much, but it can be a pretty solid theory.
Meh. I don't want to think about this anymore because this is confusing lol.
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I think the chicken. Or going back, not literally a chicken as we know it today, but other types of creatures that mutated/evolved into the chicken, which had themselves evolved from other lifeforms. There was a discovery a while back that the creation of eggs is only possible due to a protein found in chicken’s ovaries. So yeah, I think the creature came first, reproduced via laying eggs, and eventually a chicken happened xD Like I don't think the question literally means a chicken, just any egg-laying creature.