What Came First, the Chicken or the Egg? Not Even Close

At least 125 million years separate the first amniotes in the fossil record from the oldest preserved eggshell anyone has ever dug up. That gap is stated outright by Koen Stein and colleagues in Scientific Reports, and it changes what the riddle is asking.

The answer itself is settled and dull. What has moved is the evidence underneath it: three of the facts people carry into this argument have been overturned, two of them since 2022.

What came first, the chicken or the egg?

The egg came first, by hundreds of millions of years. Egg-laying land vertebrates called amniotes were leaving footprints about 355 million years ago, while the oldest confirmed bones of a domestic chicken date to roughly 1650 to 1250 BCE in Thailand. Eggs existed long before any chicken did.

The 2010 headline was a chemistry paper

In July 2010 the story went round that British scientists had settled it in the chicken’s favour. NBC News ran it with a line from Colin Freeman of Sheffield University: “It had long been suspected that the egg came first but now we have the scientific proof that shows that in fact the chicken came first.”

The paper under that sentence was Freeman, Harding, Quigley and Rodger, “Structural Control of Crystal Nuclei by an Eggshell Protein,” in Angewandte Chemie International Edition, volume 49, issue 30, pages 5135 to 5137. Its published abstract opens “Growing a good egg” and reports metadynamics simulations in which the eggshell protein ovocleidin-17 induces calcite crystals to form out of amorphous calcium carbonate nanoparticles, then proposes a catalytic cycle for the first stages of shell formation.

The study that supposedly settled the riddle was a computer simulation of calcium carbonate crystallising, and its published abstract is about a catalytic cycle inside a hen rather than about which animal arrived first. No fossil is examined. No date is proposed for anything. Confident answers about animals travel much further than the evidence behind them, which is also the story of what a hyena is doing when it giggles.

The amniote date moved in 2025

In 2025, John Long and colleagues published “Earliest amniote tracks recalibrate the timeline of tetrapod evolution” in Nature. A single track-bearing slab from the Snowy Plains Formation at Barjarg, on Taungurung Country in Victoria, Australia, carries footprints with sharp claw impressions, which mark the trackmaker as a crown-group amniote rather than an amphibian.

The rock sits in the early Tournaisian, probably 358.9 to 354 million years old. That pushes the likely origin of crown-group amniotes back by at least 35 to 40 million years from the previous molecular estimate, whose median age across thirty studies was 319 million years. Any page still putting the first egg-layers at around 319 million years is working from the number this slab displaced.

The shell arrived 125 million years late

An amniote is an animal whose embryo develops inside its own set of membranes, and that membrane system is the invention the riddle’s “egg” refers to. A hard chalky shell is a separate and much later idea. Inside a hen, the ovum is fertilized at the top of the oviduct before its white, membranes and shell are added further along.

The oldest known amniote eggs are Early Jurassic, from the Sinemurian, 195 to 192 million years ago: sauropodomorph dinosaur eggs whose calcareous layer measures only 60 to 100 micrometres over a thick fibrillar shell membrane. Stein’s team read those as thin but rigid. A 2020 Nature paper led by Mark Norell reached the opposite conclusion about what came before them, reconstructing the ancestral state and finding that the first dinosaur egg was soft-shelled, with the calcified hard-shelled egg evolving independently at least three times across the Mesozoic.

The egg of the answer and the egg of the riddle are not the same object. Amniotes were laying eggs on land for well over a hundred million years before anything laid one with a shell hard enough to fossilise.

Stein’s team measured that blank stretch at 125 million years against the amniote dates available in 2019. The Australian trackway stretches it to roughly 160. Whole chapters of animal reproduction stay off the record like this, which is why nobody has ever watched an eel spawn in the wild either.

The chicken is about 3,600 years old

In 2022 a team led by Joris Peters and Greger Larson assessed more than 600 archaeological sites across 89 countries for PNAS and placed the first unambiguous domestic chicken bones at the Neolithic moated site of Ban Non Wat in Thailand, dated to about 1650 to 1250 BCE, where more than 95% of the bird bones belong to Gallus.

They deal with the older claims directly: “Previous claims for the presence of chickens in the Yellow River basin 11,000 to 8,000 y ago are not supported by either the climatic, palynological, or archaeofaunal records,” and a reanalysis of those bones found the remains were not chickens.

A companion paper in Antiquity radiocarbon-dated 23 chicken bones from presumed early contexts. Eighteen of the 23 returned dates later than their stratigraphy suggested, only five matched their reported phasing, and no chicken turns up in Europe before the first millennium BC. Peters’s team proposes an agricultural trigger: fields of millet and rainfed rice, and the fallow ground beside them, may have drawn red junglefowl in towards human settlements. The chickens kept at least one junglefowl habit: a rooster’s dawn crow descends from the red junglefowl’s territorial call, and its timing comes from a clock inside the bird rather than from the sunrise.

Event	Date	Source
Oldest amniote tracks	358.9 to 354 million years ago	Long et al., Nature, 2025
Oldest known amniote eggs	195 to 192 million years ago	Stein et al., Scientific Reports, 2019
First unambiguous chicken bones	about 1650 to 1250 BCE	Peters et al., PNAS, 2022
Chickens reach Mediterranean Europe	about 700 BCE	Peters et al., PNAS, 2022

There is no first chicken

The riddle’s second move is the definitional dodge, the one that asks whether you meant a chicken’s egg specifically. That version assumes a first chicken existed, one bird standing on the far side of a line its parents were on the near side of. No such bird hatched. Domestication is a process, and the boundary between red junglefowl and chicken is a label applied afterwards to a continuum.

The genetics push harder still. Yellow skin in domestic chickens does not trace to the red junglefowl at all. Jonas Eriksson, Greger Larson and colleagues traced the allele to another junglefowl species, most likely the grey junglefowl, Gallus sonneratii, and called their result “the first conclusive evidence for a hybrid origin of the domestic chicken” in PLoS Genetics. The chicken is not the tidy descendant of one wild species, which makes a single founding bird harder to imagine than ever.

Labels get applied after the fact and then set like concrete, which is roughly how a US state ends up better known by a nickname than by its name.

So the egg wins, by a margin large enough to stop meaning much. What survives is the shape of the question, which asks which end of a loop came first while handing you a species boundary biology never drew and a hard shell that shows up 160 million years after the egg it covers. Both of those parts were painted on later, by people who needed the riddle to have two ends. Strictly FYI.