Chicken or egg? A zoologist’s attempt to solve the riddle came first

The chicken or the egg? Sometimes, as a zoology author, I am asked this question by the little boy in the front with the raised hand and big questioning eyes. Sometimes it’s the older man in the back with a glint in his eye. Sometimes it is a student who comes to the lectern at the end of a lecture while everyone else is leaving. The same mischievous eyes, the same wry smile. “So what came first?” they ask, beaming, unaware that this is the case not the first time I was asked.

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 did not anticipate that this would become virtually the only question I would be asked. I have spent years reframing the evolution of life on Earth as a story told from the perspective of the egg, exploring the adaptation of this strange ship to land, its movement across continents, the evolution of the umbilical cord, the evolution of the placenta, menstruation, menopause… even now that I’ve finally turned this journey into a book, I expect that much of my dialogue with readers will be chicken-based.

Luckily, I consider chickens to be a fascinating gateway for anyone who’s never really thought about how strange and beautiful animal eggs are when you stop to think about them.

So the question at hand: chicken or egg? What really came first?

Like an egg, the question itself needs some space to breathe. The chicken-and-egg paradox – the classic causality dilemma – playfully expresses the difficulty the human mind has in sequencing actions where one depends on the other being done first and vice versa. Aristotle, writing in the fourth century BC, considered it an example of an infinite series, without a real beginning. It was a way to imagine what infinity represents. Later, Plutarch, the Greek historian and biographer, spoke of the chicken and the egg as a “great and grievous problem” that forced philosophers to deal with questions about whether the world had a beginning or would ever end. The chicken and the egg were in a sense the precursors of modern questions about cosmology, deep time and physics. Later, through a series of exciting discoveries in the 19th century (particularly the ideas of Charles Darwin and Alfred Russell Wallace, co-discoverers of natural selection), biologists and geologists were able to provide a more evidence-based perspective on the ancient history of nature. ask. And so what follows in the next paragraph is the standard answer you are likely to get if you ask a contemporary zoologist a “chicken or egg” question.

A more thought-provoking way to approach the question is to ask, “Which came first, the egg or the egg boiler?”

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, all of which lay eggs, go back a long time in history, many millions of years, while chickens have been around for less than 10,000 years, according to DNA research and archaeological evidence. So the answer to the paradox is simple. Egg wins. A country mile. In some (but not all) dinosaur groups, one of which was the ancestor of today’s birds, shell eggs evolved about 160 million 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, you have it: the egg, almost 200 million years old, is considerably older than the chicken, which is at most about 0.01 million years old.

But that doesn’t give you a satisfying feeling. My problem with this zoological answer is that it sells the egg short. Because eggs are indeed very varied. These numerous organic vessels, whose primary function is to fire genetic lineages through time, deserve a little more space to… cook. So when I ask this question, I like to go into more detail.

A more thought-provoking way to approach the question is to ask, “Which came first, the egg or the egg boiler?” Because it is not the chickens, but the egg tubes (known to humans as fallopian tubes) that cause many eggs to look like this. Egg tubes are plentiful in the animal kingdom. From egg tubes that leak milk from the walls like the eyes of holy statues (see: some flies), to egg tubes that stick cement-like glue over the eggs so they can be stuck to human hair (see: head lice). There are egg tubes in which embryos struggle and fight to the death (see: some sharks); egg tubes inhabited by blood-sucking placentae (see: some mammals); egg tubes flanked by paired vaginas (see: marsupials).

The chicken egg tube is truly astonishingly beautiful. Every goose egg you’ve ever held was first clothed in a dizzying, constricted, complicated lifespan. Every egg you’ve ever cracked or boiled into a mixing bowl and served with soldiers who graduated it. Deep inside the chicken, the egg you held in your hand started out as a gloomy, slimy blob. As it passed through the egg tube, it was attended to by glands in the walls of the egg tube that spotted various chemicals onto the egg, almost as if it were a vehicle going through a car wash. Some sprinklers sprayed a frothy, calcium-rich layer that hardened into a shell. Some squirted small pencil-like marks onto the eggshell; others painted constellations from dots and spots. In some birds, these little nozzles can produce eggs in all kinds of blues and greens. The blackbird (placed in a bush near you in spring and early summer) looks almost as if it has been carved into jade. There are even pores in the wall of the chicken’s egg case, which secrete a waxy layer on the outer shell of the egg to protect it from microbes. And then the egg is delivered, like a shiny executive car at a car lot, polished and ready to go.

What came first: the egg or the tube that made it? Why would an egg tube evolve if there was no egg to serve? How could there be an egg if there was no egg tube? We go deeper. The truth is that the egg has come a long way before the evolution of the egg tube, and by a wide margin – many millions of years, clearly visible in the fossil record. In jellyfish, one of the very first animals thought to have evolved, the eggs are grown inside the body and then released directly into the water, often by the thousands. Perhaps the first eggs were shed this way.

Eggs are truly ancient. They go back 600 million years or more, as documented by discoveries of spherical specimens found in slabs of ancient seabeds. Some are barely a millimeter wide and some look surprisingly intact. Some even have so-called primitive cells within them – two, four, eight, sixteen – that divide to become new life: an embryo, a young, a generation. The truth is, we don’t know much yet about the animals that hatched from these mysterious prehistoric eggs. Some are said to be jellyfish; others may have been primitive marine worms. Anyway, 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) really got going. The very idea of ​​the existence of a chicken – a walking, screeching, feathered creature with an internal skeleton, eyes and a beak enriched with minerals – would have been unthinkable at the time for something that captured the imagination. But incredibly, the egg probably goes back even further in time.

If you expand the parameters of the question to allow the inclusion of sex cells (gametes), for example, eggs and sperm, then eggs beat chickens by a billion years. The uniformity and commonality of sex among distantly related contemporary groups, such as algae, plants, and animals (then mostly little more than single-celled specks, sucking up detritus from rocks), suggests that eggs and sperm probably evolved somewhere around 1 billion. years ago. This leads us to the conclusion that there were eggs and sperm on this planet long before animals as we know them evolved. This was long, long, before egg tubes.

And so in this great paradox of the past 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 ready myself for one final flourish. Because the paradox, like the egg, still has many fascinating layers that continue to attract the human mind.

For example, there are genetics to consider. There must have been a point in time when the chicken’s ancestor, the wild junglefowl, laid a fertilized egg containing the exact combination of mutations that gave rise to the lineage then given the spoken label “chicken” (or its equivalent in the early language). . And what exactly is a “chicken”? The chicken of old, who strode through the backyards and pecked at grain? Or today’s broilers, the monstrous perversion created by the poultry industry? What we call a “chicken” is in reality, viewed across the millennia, a tumbling river of genes and genetic lineages flowing forward in time, shuffling in and out of new combinations as the generations pass, chiseled and refined by the whims of unthinking planetary surface forces. or, more commonly for this species, the sculpting, selective hands of industry. Like countries on continents, the concept of “chicken” only exists because there is an upright ape on this planet with a penchant for categories and a penchant for labeling things as they are at this precise geological moment in Earth’s history. And what are animals anyway? 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 egg tubes? Eggs or animals? An enduring paradox conceived 2,000 years ago remains, at least in my eyes, as delightful and exciting to ponder as ever. We live in an age of science, of rigorous 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 leftmost bookend for all animal life. Modern graduate of the egg tube. Truly a wonderful thing.

  • Infinite life: a revolutionary story about eggs, evolution and life on earth by Jules Howard is published by Elliott & Thompson (£20). In support of the Guardian And Observer Order your copy at Delivery charges may apply

Leave a Comment