It’s that old riddle it is sparked many debates through the ages: was itthe chickenor the egg thatcame first? It’s together a tricky questionbecause you require a chicken come lay one egg,but chickens come from eggs, leaving us with an intractable circle of clucky, feather life the apparently has actually no clear beginning point.

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Thankfully, yes no must keep brooding end this forever. This is a riddle we have the right to unscramble with the devices of—more special, the ethics of evolutionary biology.

Let’s obtain cracking.

The first eggs

Eggs are found throughout the pet kingdom. Technically speaking, one egg is merely the membrane-bound vessel inside which an embryo deserve to grow and also develop until it can survive on its own.

Eggs of all shapes and sizes exist throughout the pet kingdom. Image adapted from: Adolphe Millot; CC0

But let’s emphasis on the type of bird"s egg us recognise today. These first came top top the scene with the development of the an initial amniotesmany millions of years ago. Prior to their arrival, most pets relied on water because that reproduction, laying their eggs in ponds and other moist settings so the the egg didn’t dry out.

At some point, a various kind of egg began to evolve, which had actually three extra membranes inside: the chorion, amnion and also allantois. Each membrane has actually a contempt different role but the enhancement of every these extra layers provided a conveniently enclosed, all-in-one life support system: one embryo have the right to take in stored nutrients, save excess rubbish products and respire (breathe) there is no the require of an exterior aquatic environment. The extra fluids encased in the amnion, add to the challenging outer shell, carry out extra security too.

Diagram the a chicken egg in its 9th day—an example of an amniotic egg. Image adjusted from: K.D. Schroeder; CC-BY-SA 3.0

Amniotic eggs were a huge deal. They opened up up a whole new world of methods for land-based egg-laying locations, and also the extra membranes paved the method for bigger (and mostly better) eggs.

We’re quiet not certain of precisely when this happened, largely because eggy membranes don’t make very an excellent fossils, leaving researchers with no clear document of when, or how, amniotic eggs developed. Our best guess is the the last common ancestor the both tetrapods (four-limbed pets with a backbone) and the amniotes (four-limbed animals with a backbone that lay eggs with all those extra layers) lived roughly 370-340 million year ago, though some sources placed the very first amniote species as life closer to 312 million year ago. Today’s mammals, reptiles and birds space all descendants of the very first amniotes.

(This leaves united state with an additional eggsellent question: which come first, the amniote or the amniotic egg? but let’s just stick with chickens for now.)

The first chickens

The very very first chicken in existence would have actually been the an outcome of a hereditary mutation (or mutations) following in a zygote produced by two almost-chickens (or proto-chickens). This way two proto-chickens mated, combining their DNA together to kind the very an initial cell the the very an initial chicken. Somewhere along the line, hereditary mutations developed in the very very first cell, and also those mutations replicated themselves right into every other body cell as the chicken embryo grew. The result? The an initial true chicken.

A masculine red junglefowl, the closest ancestor come the modern-day domestic chicken Image adjusted from: Philip Pikart; CC-BY-SA 4.0

So who were the likely parents of this an initial One True Chicken? The red junglefowl (Gallus gallus) is aboriginal to a selection of south-eastern eastern countries consisting of India, southern China, Indonesia, Malaysia, Singapore and Indonesia. It’s thought that the red junglefowl was tamed by people in Asia and also went on to it is in spread approximately the people as the less-aggressive and also prolific egg-layers that us know and also love today (Gallus gallus domesticus).

Archaeological evidence says that the red junglefowl was first domesticated some 10,000 year ago, although DNA analysis and math simulations indicate that the residential chicken in reality diverged native junglefowl much previously (an estimated 58,000 years ago). There’s additionally evidence to imply that the domestic chicken’s origins might be slightly much more complicated: the gene for the yellow colour seen on the legs of plenty of chooks might have come native the grey junglefowl (Gallus sonneratii), not the red, pointing to some hybridisation between types somewhere along the way.

Back come our original question: v amniotic eggs mirroring up about 340 million or so year ago, and the an initial chickens evolving at about 58 thousand years earlier at the earliest, it’s a safe bet to say the egg come first.

Eggs were around method before chickens even existed. Image adapted from: Sketching (with permission).

The very first chicken eggs

But wait—weren’t over there some scientists who claimed that, in fact, the chicken came first?

This case came from some researchers studying exactly how chicken eggshells form. Eggshell is greatly made native calcium lead carbonate (CaCO₃). Hens gain their supply of calcium because that eggshell production from dietary resources (calcium-rich seafood shells, such together oyster or prawn shells, space a famous snack for backyard hens for this reason).

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To type a shell, the calcium needs to be deposit in the form of CaCO₃ crystals, and hens count on details proteins that permit this process. One such protein, referred to as ovocleidin-17 (or OC-17 because that short), is only discovered in the ovary that a chicken, bring about the pointer that the chicken must have come prior to the chicken egg, because without OC-17, there deserve to be no chicken egg formation. (Interestingly, it seems that this protein is responsible for accelerating the rate of eggshell formation, permitting hens to develop an egg from scratch and also lay it in ~ a 24-hour timeframe.)

Domestic chickens room extremely efficient egg layers, qualified of developing a new egg around every 24 hours. Image adjusted from: Australian Academy of scientific research

So, can we lay this age-old conundrum to rest? Or are scientists and philosophers tho scrambling to uncover an answer?

At the end of the day, the question is something of a false dichotomy. Eggs definitely came before chickens, yet chicken eggs did not—you can’t have one there is no the other. However, if we absolutely had actually to pick a side, based upon the evolutionary evidence, we’re top top Team Egg.

This short article was written by Emma Berthold, content Producer, Australian Academy the and has to be reviewed by the following experts: Professor rick Shine am FAA Professor of evolutionary Biology, college of biological elafilador.nets, college of Sydney; Associate Professor Trevor Worthy Vertebrate palaeontologist and Vice-Chancellor"s Postdoctoral research Fellow, college of and also Engineering, Flinders University; Dr Walter Boles senior Fellow, Ornithology Section, Australian Museum