I answer it with evolution, so the egg came first, and the first chicken came from an egg laid by something very close to, but not quite, a chicken.

But it also makes me wonder: How far apart in mutations does something have to be before it is considered an entirely new thing?

The chicken came first. Chicken-ness begins at conception.

This conversation has been swirling since forever, and the answer is that both came first

It really comes down to the fact that we have arbitrary scientific conventions, and we have to slot everything into its little hole

It is impossible to make the determination, outside of the human perspective, which came first

In one sense, the egg. Animals had been laying eggs for millions of years before anything like a chicken evolved.

If we’re limiting our scope to just chicken eggs though, things get a little murkier.

When we talk about chicken eggs, are we talking about eggs laid by a chicken, or are we talking about eggs from which a chicken can hatch? Or do both need to be true for it to truly be a chicken egg?

In the first and last case, the chicken obviously needs to come first, a non-chicken can’t lay a chicken egg if that’s the criteria you’re going by.

That middle ground though is interesting.

The chicken is descended from the red junglefowl. Look up some pictures, they’re pretty damn chicken-y, I might even say they may look even more like a chicken than some modern chicken breeds. If I was out walking around and a junglefowl ran across the street in front of me, I’d probably chuckle to myself while I pondered the age-old question of “why did the chicken cross the road?” If one showed up in my friends’ backyard flock of assorted chicken breeds, it wouldn’t look at all out of place.

But it is not a chicken.

Chickens, however, are junglefowl. We consider them to be a subspecies of junglefowl- Gallus gallus domesticus

Chickens did not emerge in a single instant. It took many years of selective breeding and evolution for the modern chicken to come into being. Countless generations of junglefowl gradually becoming more chicken-y until the modern chicken emerged.

At one point in time, a bird was hatched that checked all of the boxes for us to call it a chicken instead of a junglefowl. The egg it hatched from was laid by a bird that was just on the other side of the arbitrary line from being a chicken. Unless you sequenced the two birds genomes you would probably be pretty hard-pressed to say which was the chicken and which was the junglefowl.

So the first chicken hatched from an egg said by a junglefowl.

However, that is one true chicken in a flock of not-quite-chickens. Odds are that chicken did not breed with another true chicken, but instead one of those near-chicken junglefowl. So its eggs would not hatch into a true chicken, but instead a chicken-junglefowl hybrid.

And there was probably a long period of time where things teetered on that line, the occasional true chicken hatched, and then laid eggs that hatched into non-chickens, those non-chickens getting closer and closer to the line over many generations.

Until finally it happened. Two true chickens bred, and lay an egg that also matches into a true chicken. The first chicken hatched from an egg laid by a chicken.

But again you’d be pretty hard pressed to pinpoint which bird that was in the flock. It was probably a wholly unremarkable bird that looked pretty much the same as all of the chickens and non-chicken junglefowl around it.

The lines we draw separating different species and subspecies are pretty arbitrary. It’s more for our convenience to categorize things than it is to reflect any absolute truth about the animals around us. That line could have been drawn just about anywhere in the history of chickens and it would still be valid.

There’s also potentially a nature vs nurture angle here. Chickens are social creatures who raise their young, they’re not running on pure instinct, to some extent they learn how to be a chicken from other chickens. A true chicken raised by junglefowl may act more like a junglefowl than a chicken in some ways, and vice versa. Is that important when determining what the bird is? When the differences between them are so small, I think it might be. As they say, if it looks like a duck, swims like a duck, quacks like a duck, it’s probably a duck.

So there’s perhaps an argument to be made that maybe the first true chicken didn’t appear until at least a generation or two after that first chicken hatched from an egg laid by a chicken. After all, if the young aren’t being raised by and around other chickens, maybe they’re not really chickens.

The egg… laid by a bird that wasn’t a chicken

Neil D Tyson

The explanation goes as follows:

Since any offspring is never going to be 100% genetically similar to its parent, eventually an offsprings genome will mutate into what we humans would classify as a chicken within our “scientific” definitions.

Imo the concept of a chicken is an illusion. It’s a bird thing that I can eat, and sometimes they’re really nice and lay eggs, that’s what a chicken is.

The chicken. When it decided to cross the road

That’s a statement not a question

Anyway, the hen came first which then traveled back in time to lay the egg first, so it then could hatch into the chicken.

It’s a language question, not a biological one.
The answer is “depends on your definition of chicken and egg”.
“Chicken” isn’t a thing that exists in nature, it’s a category humans assign to some birds.

According to Last-Thursdayism, both came at the same time - last Thursday, when the universe was created

Eggs predate chickens. Chicken eggs evolved simultaneously with chickens. There was no first chicken, nor first chicken egg.

Define “chicken”

egg was being used by a lot of lizards and sea life long before chickens came around

Trust me, when it comes down to chickens, the chickens always come first.

Why? Because they are vicious little buggers, and if you try to make them wait they will eat you.

"Oh, hello monkey, is that a treat for me in your hand? How lovely, nom nom nom. What? I took your finger with the lovely dried bug? So sorry. Oh, hello monkey, is that an open wound in your hand for me? Nomnomnom. What? I’m not supposed to devour the flesh from your bones? So sorry. Oh, hello monkey, is that a bone sticking out from where your finger used to be…

You get the idea.

So, I can say with authority that if the egg had come first, the chicken would have eaten it.

Eggs existed for millions of years before chickens, why is this still a debate?

The egg is the only possible correct answer to this.

Modern chickens didn’t exist until something like 10,000 years ago. The egg was a key development in allowing animals to live on land, and first came about somewhere around 300 million years ago.

But if you want to narrow it down to just chicken eggs, then you have it right. The immediate predecessor to the first thing that can be called a ‘chicken’ laid a chicken egg from which hatched a chicken.

The egg absolutely came first.