Above: Image © istockphoto.com/Graffizone
Did you know? Chickens and other birds evolved from reptiles, and they still have some reptile DNA.“Which came first, the chicken or the egg?” You’ve probably heard the question. Have you ever tried to answer it? Of course, a philosopher would say that the question doesn’t really have an answer. It’s a circular dilemma that can be pondered and debated forever. But scientists are equipped to provide an answer! Several answers, in fact, depending on the definitions they use.
First let’s make sure we really understand the question. Of course, it doesn’t refer to just any kind of egg. After all, dinosaur eggs existed long before chickens did. So what the question really means is: “Which came first, the mother chicken or the chicken egg?”
Every chicken is born from a chicken egg. You need a mother to lay the egg. But each chicken’s mother also came from an egg. Is your head spinning yet?
To properly answer the question (the one about the chicken, not the one about your head spinning), we need to be clear and precise. To begin with, what is a chicken? We need a definition that will tell us if an animal “ is a chicken” or “isn’t a chicken” (“maybe” is not an option!).
Did you know? The chicken was the first bird to have its entire genome sequenced.Let’s use DNA, because it’s a sort of recipe for making a chicken. The DNA of a chicken fetus inside an egg is the same as the DNA of the chicken that grows out of it.
However, the animal that laid the chicken egg wasn’t necessarily a chicken. Do you have exactly the same DNA as your mother? No, because approximately half of your DNA comes from your father. So two almost-but-not-quite-chicken parents could have a baby chicken.
That’s how the first ever chicken was born. With a bit of evolutionary luck, the most chicken-like parts of these parents’ DNA came together to make a baby chicken. Or rather, the almost-but-not-quite-chicken mother laid a chicken egg, from which a baby chicken emerged. So the egg comes first: before a chicken can be born, there must be an egg! And the egg didn't necessarily come from a chicken.
That settles it, right? Not quite! Because by using slightly different definitions, we arrive at a completely different answer.
For example, in 2010, scientists at the University of Warwick focused their attention on the shell instead of the chicken fetus inside. They defined “chicken-ness” as the ability to lay eggs with that kind of shell (the poor roosters must have felt very left out!).
Did you know? Hens that are specially bred for egg production lay about 300 eggs per year.This approach changes the question completely, because the shell was made by the hen that laid the egg. And if the hen could lay a chicken egg, she must have been a chicken. However, she might have been born from an egg with a non-chicken shell. So by using a different definition, we get a different answer: the chicken came first.
What do you think? Did the chicken come first? The egg? Or is the questions best left to the philosophers?
Most of the content of this article was developed for classroom visits and during discussions with students. We would like to thank C.E. Barry Intermediate School in Hope, B.C., and Agassiz Elementary Secondary School in Agassiz, B.C., for their participation.
Scientists reverse evolution with snouted chicken (Nick Colins, The Telegraph UK) Science answers the question: Which came first, the chicken or the egg? (Lesley Ciarula Taylor, Toronto Star) Researchers Compare Chicken, Human Genomes (National Institutes of Health)
Poultry and Egg Market Information (Agriculture and Agri-Food Canada)
Building a Dinosaur from a Chicken (Jack Horner, TED Talks)
Freeman C et al. 2010. Structural Control of Crystal Nuclei by an Eggshell Protein. Angewandte Chemie. 49(30):5135–5137.