Chicken or egg? Sometimes, as a zoology writer, I am asked this question by a child in the front with his hand raised and looking with questioning eyes. Sometimes it’s the old man in the back with twinkling eyes. Sometimes, at the end of the lesson, when everyone is leaving, there will be a student approaching the podium. The same mischievous looks, the same sarcastic smile. “So which one came first?” they ask laughingly, unaware that this is happening Negative This is the first time I’ve been asked.
Many years ago, when I began researching the evolution of the animal egg and the role it has played in the long history of life on this planet, I had no idea that this would be the only question I would be asked. I have spent years reframing the evolution of life on Earth as a story told from the egg’s perspective; I traced this strange ship’s adaptation to land, its movement across continents, the evolution of the umbilical cord, the evolution of the placenta, menstruation, menopause… Even now that I have finally turned this journey into a book, I expect much of my dialogue with readers to be chicken-based.
Luckily, I find chickens to be a fascinating gateway species for those who have never considered animal eggs when you consider for a moment how strange and beautiful they are.
So, the question at hand is; chicken or egg? Which one really came first?
Like an egg, the problem needs some room to breathe. The chicken and egg paradox – the classic causality dilemma – playfully expresses the difficulty the human mind has in ordering actions where one thing depends on another being done first and vice versa. Aristotle, writing in the 4th century BC, thought this was an example of an infinite series with no real beginning. It was a way to imagine what eternity represented. Later, the Greek historian and biographer Plutarch spoke of the chicken and the egg as a “great and heavy problem” that forced philosophers to preoccupy themselves with questions such as whether the world had a beginning or whether it would one day end. In a way, the chicken and the egg foreshadowed modern questions about cosmology, deep time, and physics. Later, thanks to a series of exciting discoveries in the 19th century (notably the ideas of Charles Darwin and Alfred Russel Wallace, who discovered natural selection), biologists and geologists were able to offer a more evidence-based perspective on centuries-old creatures. question. So, in the next paragraph, here is the standard response you will get when you pose the “chicken or the egg” question to today’s zoologists.
A more thought-provoking way to approach the question is to ask: ‘What came first, the egg or the egg tube?’
If you think of the egg as something with a hard shell that you can break with a spoon, it means that the egg came long before chickens. Because the history of all egg-laying birds goes back a long way, millions of years ago; However, according to DNA studies and archaeological evidence, chickens have been around for less than 10,000 years. So the answer to the paradox is simple. The egg wins. About a mile. In fact, shelled eggs evolved about 160 million years ago in some (but not all) groups of dinosaurs, one of which is the ancestor of today’s birds. Other groups of dinosaurs, including the earliest long-necked dinosaurs known as Sauropods, may have developed shelled eggs as early as 195 million years ago. And so, in literal terms, there you have it: the egg, which is almost 200 million years old, is much older than the chicken, which is at most 0.01 million years old.
But this doesn’t feel satisfactory. My problem with this zoological response is that the egg is shortchanged. Because eggs are truly diverse. These multitudes of organic pots, whose primary function is to fuel genetic lineages forward in time, deserve a little more room for cooking. I like to elaborate when asked this question.
A more thought-provoking way to approach the question is to ask: “Egg or egg tube first?” Because it’s not the chickens that make many eggs look that way, but the egg tubes (known as oviducts; fallopian tubes in humans). Egg tubes are abundant throughout the animal kingdom. From egg tubes that leak milk from their walls like the eyes of sacred statues (see: some flies), to egg tubes that stick cement-like glue all over the eggs so they can stick to human hair (see: head lice). There are egg tubes where embryos fight and wrestle to the death (see: some sharks); egg tubes in which blood-sucking placentas live (see: some mammals); egg tubes surrounded by paired vaginas (see: marsupials).
The chicken’s egg tube is truly stunningly beautiful. Every chicken egg you held in your hand first took on a dizzying, narrow, complex corridor of life. Every egg you’ve ever cracked into a mixing bowl or boiled and served with graduate soldiers. Deep inside the chicken, the egg you hold in your hand started out as a lumpy, slimy blob. As it passed through the egg tube, it was controlled by glands on the walls of the egg tube that sprayed different chemicals onto the egg, like a vehicle going through a car wash. Some nozzles sprayed a calcium-rich foamy layer that hardened into a crust. Some squeezed small pencil-like marks onto the eggshell; others drew dots and constellations of dots. In some birds, eggs can be made in all kinds of blue and green colors thanks to these tiny nozzles. The blackbird egg (which lays in a bush near you in spring and early summer) looks as if it were carved from jade. There are even pores in the wall of the hen’s egg tube that secrete a waxy layer to protect the outer shell of the egg from microbes. The egg is then delivered polished and ready to go, like a shiny executive wagon on a forecourt.
Which came first, the egg or the tube that makes it? Why would an egg tube evolve if there was no egg to serve? How could an egg exist if there was no egg tube? We go deeper. The fact is that the egg appeared long before the evolution of the egg tube, and by a huge margin of millions of years, as is clearly visible in the fossil record. In jellyfish, one of the first animals thought to evolve, thousands of eggs often grow inside the body and are then shed directly into the water. Maybe this is how the first eggs were laid.
Eggs are very old indeed. They date back 600 million years or more, as documented by the discovery of sphere-like specimens found on ancient sea floors. Some of them, just a millimeter in diameter, look surprisingly sturdy. Some even have allegedly primitive cells inside them — two, four, eight, 16 — dividing to create a new life: an embryo, an offspring, a generation. The truth is that we don’t yet know much about the animals that hatched from these mysterious prehistoric eggs. Some are claimed to be jellyfish; others may be primitive marine worms. Either way, these eggs are very old. Much older than chickens or egg tubes. These fossil eggs date back to the Ediacaran period, about 100 million years before animals (as we know them) actually took off. The idea of the existence of a chicken—a walking, squawking, feathered creature with a mineral-enriched endoskeleton, eyes, and a beak—was unimaginable to any imaginative person at the time. But incredibly, the egg probably goes back further than that.
If you expand the parameters of the problem to allow for the inclusion of sex cells (gametes, e.g. ovary and sperm), then eggs beat chickens by 1 billion years. The uniformity and commonality of sex among such distantly related modern-day groups as algae, plants, and animals (then little more than single-celled specks, collecting debris from rocks) suggest that eggs and sperm likely evolved around 1 billion years ago. Years ago. This leads us to the conclusion that eggs and sperm existed on this planet long before animals as we know them today evolved. This was long, long before egg tubes.
And in this great paradox of the last thousand years there is the egg. Always eggs. The egg is older than the chicken. Next time I’m asked, I’ll say this before bracing myself for one last flourish. Because paradox, like the egg, has many impressive layers that still attract the human mind.
For example, there are genetics to consider. There must have been a moment when the wild grouse, the ancestor of the chicken, laid a fertilized egg; Inside this egg was the exact combination of mutations that gave rise to the lineage later verbally called “chicken” (or its early language equivalent). . So what exactly is “chicken”? The old chicken wandering around backyards pecking at grain? Or is it today’s chickens, the monstrous perversion created by the poultry industry? What we call “chicken” when viewed over thousands of years is actually a flowing river of genes and genetic lineages flowing forward in time, moving in and out of new combinations as generations pass, shaped and expertly shaped by the whims of unthinking planetary surface forces. or, more commonly for this genre, the sculpting, selective hands of the industry. Like countries across continents, the concept of “chicken” exists because there is an honest monkey on this planet who has a penchant for categories and enjoys labeling things at this precise geological moment in Earth history. So what are animals really? Are animals organisms that produce eggs to make more animals? Or are animals evolutionarily vessels for eggs to make more eggs?
Chicken or egg? Egg or egg tube? Eggs or animals? An enduring paradox imagined 2,000 years ago remains, at least in my eyes, always as delicious and exciting to contemplate. We live in an age of science, definitive evidence, journals and discoveries galore, yet this simple question has the potential to exercise the mind in a very satisfying way. And so, long live the egg, the left-most bookend of every animal’s life. Modern graduate of the egg tube. It’s truly a wonderful thing.
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Eternal Life: A Revolutionary Story of Eggs, Evolution, and Life on Earth The book by Jules Howard is published by Elliott & Thompson (£20). To support Guardian And Observer Order your copy at guardianbookshop.com. Delivery charges may apply