The chicken or the egg? Sometimes, as a zoology writer, I am asked this question by the child in the front with the raised hand and big questioning eyes. Sometimes it’s the older guy in the back with a twinkle in his eye. Sometimes it is a student who approaches the lectern at the end of a lecture while everyone else is expounding. The same mischievous eyes, the same wry smile. “So what came first?” they asked beaming, unaware that it was not the first time I was asked.
I did not realize, years ago, when I began to investigate the evolution of the animal egg and the role it has played in the long history of life on this planet, that this would become more or less the only question I asked would not be I have spent years reframing the evolution of life on Earth as a story told from the egg’s perspective, and this strange craft’s adaptation to land, its movement across continents, the evolution of the umbilical cord, the evolution of tracing the placenta, menstruation, menopause… but even now, having finally turned this journey into a book, I expect a large part of my dialogue with readers to be chicken-based.
Fortunately, I consider chickens a fascinating gateway species for anyone who has never really stopped to think about how strange and beautiful animal eggs are when you consider them for a moment.
So, the question at hand – chicken or egg? What really came first?
Like an egg, the question itself needs some room to breathe. The chicken-and-egg paradox – the classic causality dilemma – playfully expresses the difficulty the human mind has in sequencing actions where one thing depends on the other being done first and vice versa. Aristotle, writing in the fourth century BC, considered this to be an example of an infinite sequence, with no true beginning. It was a way of imagining what infinity represented. Later, Plutarch, the Greek historian and biographer, spoke of the chicken and egg being a “great and weighty problem” that forced philosophers to engage with questions about whether the world had a beginning and whether it ever would. end. The chicken and the egg were, in a way, precursors to modern-day questions about cosmology, deep time and physics. Later, through a series of exciting discoveries in the 19th century (especially 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-old question. And so, what follows in the next paragraph is the standard response you’re likely to get if you throw a “chicken or egg” question to a contemporary zoologist.
If you think of an egg as something with a hard shell that you can crack with a spoon, then the egg arrived long before chickens. Because birds, which all lay eggs, go back a long time in history, many millions of years, while chickens according to DNA studies and archaeological evidence, has been around for less than 10,000 years. So the answer to the paradox is simple. Egg wins. By a country mile. In fact, shelled eggs have evolved in some (but not all) dinosaur groups, one of which was the ancestor of modern birds, about 160m years ago. Other dinosaur groups, including the earliest long-necked dinosaurs known as sauropods, may have evolved shelled eggs 195 million years ago. And so, in a very real way, there you have it: the egg, almost 200m years and more, is significantly older than the chicken, which is at most about 0.01m years old.
But it doesn’t feel satisfying. My problem with this go-to zoological reaction is that it shortens the egg. Because eggs are indeed very diverse. These numerous organic vessels, whose primary function is to fire genetic lineages forward through time, deserve a little more space to… cook. So, when asked this question, I would like to elaborate.
A more thought-provoking way to approach the question is to ask: “Which came first, the egg or the fallopian tube?” Because it’s not chickens, but fallopian tubes (known as oviducts; fallopian tubes in humans) that make many eggs look the way they do. Oviducts abound across the animal kingdom. Of egg tubes that leak milk from their walls like the eyes of holy statues (see: some flies), to egg tubes that stick cement-like glue all over the eggs, so that they can be stuck to human hair (see: head lice). There are egg tubes where embryos wrestle and fight to the death (see: some sharks); oviducts inhabited by blood-sucking placenta (see: some mammals); oviducts surrounded by paired vaginas (see: marsupials).
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The chicken’s egg tube is really stunningly beautiful. Every chicken egg you’ve ever held was first clothed in a dizzying, cramped, complicated way of life. Every egg you’ve ever cracked in a mixing bowl or boiled and served with soldiers graduated from it. Deep inside the chicken, the egg you held in your hand began as a gloomy, slimy lump. As it passed through the fallopian tube, it was tended to by glands in the walls of the fallopian tube that sprayed various chemicals onto the egg, almost as if it were a vehicle going through a car wash. Some nozzles sprayed a foamy calcium-rich coating that hardened into shell. Some sprayed small pencil-like marks on the eggshell; others painted constellations of dots and spots. In some birds the eggs can be made all kinds of blue and green by these little nozzles. The blackbird egg (laid in a shrub near you in spring and early summer) almost looks like it was carved in jade. There are even pores in the wall of the chicken’s oviduct that secrete a waxy layer to the external shell of the egg, to protect it from microbes. And then the egg is delivered, like a shiny executive wagon on a car’s forecourt, polished and ready to go.
What came first, the egg or the tube that made it? Why would an oviduct develop if there was no egg to serve? How can there be an egg if there was no fallopian tube? Deeper we go. The truth is that the egg came a long way before the evolution of the oviduct, and by an extended margin – many millions of years, clearly visible in the fossil record. In jellyfish, one of the very first animals thought to have evolved, eggs are grown inside the body and then deposited directly into the water, often in their thousands. Perhaps the earliest eggs were laid this way.
Eggs are really old. They go back 600m years or more, as documented by discoveries of spherical specimens found in slabs of ancient sea floors. Barely a millimeter or so across, some seem surprisingly intact. Some even have what is claimed primitive cells within them – two, four, eight, 16 – split to become new life: an embryo, a brood, a 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 fossil leaders go back to the Ediacaran period, about 100m years before animals (as we know them) really got going. The mere idea of the existence of a chicken—a walking, wriggling, feathered thing with an internal mineral-enriched skeleton, eyes, and a beak—would have been unimaginable to anything capable of imagination at the time. Yet, incredibly, the egg probably goes further back in time, even than that.
If you expand the parameters of the question to include gametes, e.g. ova and sperm, to be allowed, then eggs beat chickens by, give or take, 1 billion years. The uniformity and commonality of sex among distantly related modern-day groups, such as algae, plants and animals (then mostly little more than single-celled specks, sucking waste from rocks), suggests that eggs and sperm probably at some time around 1 billion developed. years back. This leads us to the conclusion that there were eggs and sperm on this planet long before animals as we know them today evolved. It was long, long, before fallopian tubes.
And so, in this great paradox of recent millennia, it is the egg. Always the egg. The egg is older than the chicken. That’s what I’ll say next time I’m asked, before I brace myself for a final flourish. Because the paradox, like the egg, still has many fascinating layers that continue to attract the human mind.
For example, there is the genetics to consider. There must have been a moment when the chicken’s ancestor, a wild junglefowl, laid a fertilized egg, within which was the exact combination of mutations that gave rise to the lineage that was then colloquially labeled “chicken” (or its early linguistic equivalent). was given. . And what exactly is a “chicken”? The chicken of old that walks around backyards pecking grain? Or the modern-day broiler, the monstrous perversion spawned by the poultry industry? What we call a “chicken” is actually, when viewed over millennia, a tumbling river of genes and genetic lineages flowing forward in time, shuffling in and out of new combinations as generations pass, chiseled and refined by the vagaries of thoughtless planetary surface forces or, more commonly for this species, the sculptural, selective hands of industry. Like countries on continents, the concept of “chicken” only exists because there is an upright monkey on this planet with a knack for categories and a penchant for labeling things as they are at this exact geological moment in Earth ‘s history stands. And what are animals, really? Are animals organisms that produce eggs to make more animals? Or are animals the vessels that use eggs in an evolutionary way to make more eggs?
Chicken or egg? Eggs or fallopian tubes? Eggs or animals? An enduring paradox, invented 2,000 years ago, remains, in my eyes at least, just as fun and exciting to consider. We live in an age of science, of rigorous evidence and 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-hand bookend for every animal life. Modern graduate of the fallopian tube. A truly wonderful thing.
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Infinite Life: A Revolutionary Story of Eggs, Evolution, and Life on Earth by Jules Howard is published by Elliott & Thompson (£20). Around the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply
