I am unaware of bird-themed riddles that have sparked more conversation and arguments than the legendary “Which came first—the chicken or the egg?”
The riddle has always especially intrigued children who faced a mind-tickling paradox. True, chickens hatch from eggs, but you also need a chicken to lay an egg in the first place, right?
Could the puzzle ever be solved?
Fortunately, we have evolutionary biology to spoil the magic of an endless argument and answer the question once and for all.
Origins of The Chicken-Egg Dilemma
The chicken-or-egg question is so ancient that its origins cannot be traced. Aristotle first wrote about it in the fourth century BC, saying that it had no true origins and that it has sort of always existed.
Some four hundred years later, Plutarch returned to the dilemma and wrote about it in his essay “The Symposiacs” in the 1st century CE. He referred to it as a difficult problem whose ultimate point is questioning whether the world had a beginning.
In Medieval Europe, with the dominance of Western Christianity, the answer was easily decided upon. The Book of Creation points out that God directly created animals. Thus, the chicken had to appear before the egg within this doctrine.
Then, the philosophers of the Enlightenment heavily questioned this stance, slowly leading to our current scientific perspective of the chicken vs egg story.
How Chickens Came To Exist?
We take chickens for granted, but they come from an extraordinary evolutionary line of birds we group in the order Galliformes. These include ground-dwelling, stocky birds like pheasants, quails, peafowl, turkeys, and – chickens.
So, what’s so special about Galliformes? First, they are probably the most successful group of ground-dwelling birds in terms of distribution, species number, and individual numbers. And that’s even if we discount the domesticated chicken, officially the world’s most numerous and widespread bird, outnumbering humans who breed them by a factor of 3 to 1.
Second, the ancestors of today’s Galliformes are likely the only branch of the avian family to survive the K-T Event – the great asteroid impact that killed dinosaurs. However, it would be more precise to say “all other dinosaurs” except for small, quail-like ground-dwelling birds (you know that birds are dinosaurs, right?)
But, what are chickens anyway?
Fowl, including various chicken fowl species, belong to the Galliformes family Phasianidae, or pheasant family, and the genera Gallus, junglefowl.
The bird we widely recognize as “chicken” is the domesticated version of the Red Junglefowl, with some other related fowl added to the gene mix. However, the domestic fowl and the Red Junglefowl share 71-79% of the genome.
Now, back to the question of chicken origins. Junglefowls (as a group) are much more ancient than the date of domestication. For example, extinct species of junglefowl have been present throughout Eurasia thousands of years ago. Moreover, the oldest fossil records of phasianids are around 30 million years old.
Genomic studies estimate that chicken domestication happened in Thailand around 8,000 years ago. Other researchers believe that chicken domestication went hand-in-hand (or wing-in-stem, if you want) with rice culturing.
Perhaps it is needless to point out, but for all these millions of years, phasianids, junglefowl, and chickens have been hatching out of eggs. There is no alternative breeding strategy.
How Eggs Came to Be?
So, if the closest chicken cousins have been around for 30 million years, could eggs be really older than that?
Of course, they could – and they are.
In the simplest terms, an egg is an organic chamber originating from a female egg cell; it carries, protects, and helps incubate the embryo inside.
All eggs have a protective membrane around them. When the embryo develops and becomes a fetus, it can break the membrane—hatch—and continue its existence outside of the egg.
Many animals—most arthropods, mollusks, and vertebrates (excluding most mammals)—lay eggs. Eggs are almost as old as multicellular life itself.
Still, not all eggs are made equal.
The Amniote Egg Revolution
During the early history of vertebrates, eggs completely depended on water to survive due to their thin membrane and simple gas exchange mechanisms. We can still see this today in fish eggs and amphibian eggs, for example. Also, many invertebrate eggs require moist conditions to thrive, even if they’re terrestrial.
The eggs of amniotes (true land tetrapod vertebrates) were a game-changer.
Unlike the simpleton fish eggs, reptiles, birds, and the freaky monotremes (the only egg-laying mammals) have evolved complex membrane systems and thicker shells that allow happy parents to lay their eggs in the fully terrestrial environment.
Amniote eggs have three additional membranes:
- Chorion
- Amnion
- Allantois
Thanks to these membranes, the embryo can absorb its nutrient reserves, breathe, and even store waste products without needing aquatic surroundings. The extra layers and fluids, plus the tougher shell, also offer physical protection (including from dehydration). In short, the amniote egg is the animal baby’s complete terrestrial life support system.
Since eggs are rarely well-preserved in fossil form, scientists are unsure when this advanced egg first evolved. The first presumed amniote probably lived some 312 million years ago. Reptiles, birds, and mammals are all descendants of this creature, which also likely produced the first amniotic (“advanced”) eggs.
Thus, we conclude that the bird egg “model” is more than ten times older than the first phasianid bird, again confirming that the egg is much, much more ancient than the chicken.
Plot Twists (For Argument’s Sake)
I hope that by now, it is clear why the egg is a much older evolutionary invention than a chicken—and all birds, for that matter. Thus, we can confidently say that the egg came first.
However, to keep up the dispute, we can look at things differently. Are there scenarios in which we could say that chicken came first?
Here’s one. Domesticated chickens are a product of the domestication process that included (and still includes) human selection and hybridization with other fowl. In that sense, the wild Red Junglefowl – the “wild chicken” certainly came before the first domesticated chicken egg. There had to be the wild chicken hen to the first hybrid-domestic chicken egg.
I admit that the above argument is a little flimsy. The truth is that the egg “wins” no matter from which side you look at the topic. However, complicating things around chicken egg origin and the chicken domestication process is a nice exercise for the mind, and it will at least allow you to have another round of friendly bickering.
I’ll underscore the word friendly here – because the arguments have been known to turn nasty.
In Conclusion
I have to break it to you like a chicken egg at breakfast time – here is where the mystery ends.
Following an evolutionary trail of both chickens and eggs, we find that the egg—the amniote bird egg we know today—definitely appeared before the chicken. This is especially true for domestic chickens, which have existed for only around 8,000 years or so. On the other hand, amniote eggs first appeared on Earth more than 300 million years ago.
Still, this causality dilemma remains an important cultural phenomenon and a great metaphor to illustrate the sometimes blurry line between cause and effect.
