by The chicken or the egg? Sometimes, as a zoological author, the child at the front asks me this question with raised hand and big questioning eyes. Sometimes it’s the oldest guy behind him with a twinkle in his eye. Sometimes it’s a student who comes to the lecture at the end of a lecture while everyone else is filing away. The same mischievous eyes, the same smile. “So which one came first?” they ask, beaming, unaware that this is no the first time I was asked.
I could not have predicted, years ago, when I began to investigate the evolution of the animal egg and its role in the long history of life on this planet, that it 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 point of view, tracing the adaptation of this strange vessel to the earth, its movement across continents, the evolution of the umbilical cord, the evolution of the placenta, menstruation, menopause … even now, having finally turned this trip into a book, I expect that a lot of my conversations with readers will be based on chicken.
Fortunately, I consider chickens a great gateway species for anyone who has never stopped to think about how strange animal eggs are when you consider them for a moment.
So the question at hand – chicken or egg? Which came first?
Like an egg, the question itself needs some space to breathe. The chicken and egg paradox – the classic dilemma of causality – playfully expresses the difficulty the human mind has in ordering actions where one thing depends on the other being done first and vice versa. Aristotle, writing in the fourth century BC, considered it an example of an infinite sequence, with no real beginning. It was a way to imagine what infinity means. Later, Plutarch, the Greek historian and biographer, spoke of the “great and serious problem” of the chicken and the egg that forced philosophers to grapple with the questions of whether the world had a beginning or whether it would ever end. The chicken and the egg were, in a way, the forerunners of today’s questions about cosmology, deep time and physics. Later, through a series of exciting discoveries in the 19th century (notably the ideas of Charles Darwin and Alfred Russel Wallace, co-discoverers of natural selection), biologists and geologists were able to offer a more evidence-based perspective on the age group. question. And so, what follows in the next paragraph is the standard answer you’re likely to get if you throw a “chicken or the egg” question at today’s zoologist.
A more exciting way to approach the question is to ask the question: ‘Which came first, the egg or the egg tube?’
If you think of an egg as something with a hard shell that you can crack with a spoon, then the egg came long before chickens. Because birds, which all lay eggs, go back a long way in history, millions of years, while chickens, according to DNA studies and archaeological evidence, have been around for less than 10,000 years. So the paradox is a simple answer. Beat eggs. Under a thousand countries. In fact, scaly eggs evolved in some (but not all) groups of dinosaurs, one of which was the ancestor of today’s birds around 160m years ago. Other groups of dinosaurs, including the earliest long-necked dinosaurs known as sauropods, may have emerged 195 million years ago. And so, in a very real sense, there you have it: the egg, at nearly 200m years and counting, is much older than the chicken, which is, at most, about 0.01m years old.
But that doesn’t feel satisfying. My problem with this zoological answer is that it changes the egg. Because eggs are very diverse indeed. These numerous organic vessels, whose main function is to pass on genetic lines over time, deserve a little more space to… cook. So, when asked this question, I like to elaborate.
A more exciting way to approach the question is to ask the question: “Which came first, the egg or the fallopian tube?” Because it’s not chickens, but egg tubes (called fallopian tubes; fallopian tubes in humans) that make many eggs look the way they do. There are many egg tubes throughout the animal kingdom. From egg tubes that ooze milk from their walls like the eyes of holy statues (see: some flies), to egg tubes that stick glue like cement all over the eggs, so they can be stuck to human hair (see: head. lice). There are egg tubes in which embryos fight and fight to the death (see: some sharks); egg tubes inhabited by blood-sucking placentas (see: some mammals); egg tubes flanked by paired vaginas (see: marsupials).
The egg tube of the chicken is very beautiful. Every chicken egg you’ve ever had was first laid in a dizzying, restricted, twisted life. Every egg you felt was put into a mixing bowl or boiled and served to soldiers who stepped out of it. Deep inside the chicken, the egg you held in your hand began as a slimy, slimy blob. As it passed through the egg tube, the walls of the egg tube were attached to glands that sprayed various chemicals onto the egg, almost as if it were a vehicle going through a car wash. Several nozzles sprayed a layer of calcium-rich foam that hardened into the shell. Some sprayed tiny pencil-like marks on the eggshell; others painted constellations of dots and spots. In some birds, the eggs can be made all kinds of blues and greens through these little nozzles. The black egg (laid in spring and early summer in a bush near you) looks almost as if it is carved in jade. There are even pores in the wall of the chicken egg tubes that extend a waxy layer to the outer shell of the egg, to protect it from microbes. And then the egg is delivered, like a shiny executive wagon on a car forecourt, polished and ready to go.
Which came first, the egg or the tube that did it? Why would an egg tube change if there was no egg in it? How could there be an egg if there was no egg tube? Deeper we go. The truth is that the egg came long before the evolution of the egg tube, and by a wide margin – millions of years, clearly visible in the fossil record. In jellyfish, among the first animals thought to have evolved, eggs are cultivated in the body and then released into the water, often in their thousands. Perhaps this is how the earliest eggs are lost.
Eggs are really ancient. They date back 600m years or more, as documented by discoveries of sphere-like specimens found in ancient sea floor slabs. Barely a millimeter or so across, some look surprisingly intact. Some even have primitive cells within them – two, four, eight, 16 – that divide to become a new life: embryo, brood, generation. The truth is that we still don’t know much about the animals that hatched from these mysterious prehistoric eggs. Some are claimed to be jellyfish; others may have been primitive marine worms. Either way, these eggs are very old. Much older than chickens or egg tubes. These fossilized eggs date back to the Ediacaran period, about 100m years before animals (as we know them) really began. The idea that a chicken existed – a walking, squawking, feathered thing with a mineral-enriched internal skeleton, eyes and beak – would have been unimaginable to anything that could imagine at that time. But, remarkably, the egg probably goes back further than this.
If you widen the parameters of the question to include sex cells (gametes), e.g. ovum and sperm, then chicken eggs blow through, give or take, 1bn years. The uniformity and commonality of sex among distantly related modern groups, such as algae, plants and animals (so usually little more than single-celled specks, debris of the rocks), suggests that eggs probably evolved and sperm at some point around 1bn. long ago. This leads us to conclude that there were eggs and sperm on this planet long before the development of animals as we know them today. This was long, long, before egg tubes.
And so, in this amazing paradox thousands of years ago, it is the egg. Always the egg. The egg is older than the chicken. That’s what I’ll say the next time I’m asked, before I prepare myself for ultimate success. Because the paradox, like the egg, still has many interesting layers that continue to fascinate the human mind.
There is genetics to consider, for example. There must have been a time when the ancestor of the chicken, a wild jungle fowl, laid a fertilized egg, within which was the exact combination of mutations that gave rise to the offspring then colloquially labeled “chicken” (or its early linguistic equivalent ). And what exactly is “chicken”? The old chicken, strolling around the backyard picking corn? Or today’s broiler, the monstrous waste that spawned the poultry industry? What we call a “chicken” is actually, when viewed over thousands of years, a tumultuous river of genes and genetic variants flowing through time, churning in and out of novel combinations of as the generations go by, being layered and refined by the whims of unthinking planetary surface forces. or, more commonly to this species, the sculptural, optional hands of industry. Like countries on continents, the concept of “chicken” only exists because there is a monkey standing on this planet who is attached to categories and appreciates labeling things as they stand at this precise geological moment in the history of the World. And what are animals, really? Are animals organisms that produce eggs to make more animals? Or are animals the vessels that eggs use, in an evolutionary way, to make more eggs?
Chicken or egg? Eggs or egg tubes? Eggs or animals? An enduring paradox, imagined 2,000 years ago, is still, at least in my eyes, as delicious and exciting as ever to think about. We live in a scientific age, with rigorous evidence and many journals and discoveries, yet this simple question has the potential to exercise the mind in a very satisfying way. And so, long live the egg, the book furthest left of all animal life. The modern graduate of the egg tube. A truly wonderful thing.
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Uncertain Life: The Revolutionary Story of Eggs, Evolution and Life on Earth by Jules Howard published by Elliott & Thompson (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply
