[Finally Revealed]*Chicken or Egg First? | Biggest Question of Universe

In 2010 a headline went around the world: “Scientists prove the chicken came first.” It is still the most-shared answer to the oldest riddle there is — and it is wrong. The real answer is clear, it has a date on it, and it comes with a twist that was only discovered in 2023. Here is the chicken-or-egg question, finally settled.

The riddle is at least 2,300 years old — Aristotle argued about it.

The verdict

The egg came first. By about 300 million years.

Eggs with shells existed long before birds, let alone chickens. The first chicken hatched from an egg laid by a bird that was almost a chicken. So the egg wins — just not a chicken egg.

The 2010 “chicken first” claim — and why it fails

Researchers at the universities of Sheffield and Warwick used a supercomputer to study ovocleidin-17 (OC-17), a protein in a hen’s ovary that speeds up the formation of eggshell crystals. Since the protein is made in the hen, the press release concluded that “the chicken must have come first”. Newspapers loved it.

The problem is the logic, not the chemistry. OC-17 helps build a chicken eggshell faster, but it is not the only way to make an eggshell: ancestors of chickens laid perfectly good shelled eggs with their own versions of the protein for millions of years. The study answered “how does a hen make a shell?” — not “which came first?”. Even one of the authors later said the headline was the media’s, not theirs.

The real answer in four steps

1. Eggs are ancient. Fish and amphibians have laid eggs for over 500 million years. The hard, waterproof amniotic egg — the kind with a shell — appeared around 320–340 million years ago, in the ancestors of reptiles, dinosaurs and birds.
2. Dinosaurs laid eggs 230 million years ago, and birds are dinosaurs. The oldest known hard-shelled dinosaur eggs date to the Early Jurassic; chicken-style eggs are a late remix.
3. Chickens are only about 8,000 years old. They were domesticated from the red junglefowl of South and Southeast Asia — a 2022 study puts it around 1650 BCE in Thailand, linked to rice farming.
4. Species change gradually, so at some point a bird that was not quite a chicken laid an egg containing a mutation that made the chick, by definition, the first chicken. That chick hatched from an egg. Egg first.

The 2023 twist nobody expected

Here is where it gets interesting. In June 2023, a study in Nature Ecology & Evolution analysed 51 fossil species and 29 living ones and found that the earliest ancestors of reptiles and birds probably did not lay hard eggs at all. They kept embryos inside the body — “extended embryo retention” — and gave birth to live young or laid eggs very late in development. The hard-shelled egg evolved afterwards.

So if you ask “did the shelled egg come before the animals that laid it?”, the answer is no — the animals came first and invented the egg. But those animals were lizard-like creatures from 300 million years ago, not chickens. For the chicken question, the egg still wins comfortably.

Five egg facts to drop at the dinner table

24–26 hoursTo make one egg inside a hen — about 20 of those hours are spent building the shell, at roughly 10 grams of calcium carbonate.

~8,000 eggsA hen’s ovary holds thousands of potential eggs at hatch; a commercial layer produces about 300 a year.

No rooster neededHens lay eggs whether or not a male is around. Supermarket eggs are unfertilised — they could never become chicks.

Egg-laying mammals existThe platypus and the echidna lay eggs, proving the egg predates not just birds but mammals too.

Blue eggsAraucana chickens lay blue eggs because of a virus that inserted a pigment gene into their DNA centuries ago.

Myth busters

Three chicken-and-egg “facts” the internet keeps getting wrong

✗Scientists proved the chicken came first.
The 2010 study explained how a hen builds a shell. It never addressed evolution — and eggs predate chickens by hundreds of millions of years.

✗Brown eggs are healthier than white eggs.
Shell colour depends on the breed of hen. Nutrition is identical.

✗The riddle is unanswerable.
It only feels that way if you assume chickens have always existed. Once you know they evolved, the egg is the obvious answer.

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Sources: Nature Ecology & Evolution (2023) – extended embryo retention in early amniotes · Nature Ecology & Evolution (2022) – chicken domestication date · TIME – the 2010 OC-17 study · LITFL – chicken or the egg, the science · Britannica – which came first?

Last fact-checked: October 2026.