Which Came First? The Chicken or the Egg?

You can’t lay an egg without the chicken… but how do you get the chicken without laying an egg? Which came first? The chicken or the egg? Talk about a paradox! So, now what if we told you that we know which one came first? Think you know? Spoiler alert! The egg came first! Read on to find out how we figured it out!

The Egg: An Evolutionary Breakthrough

Amphibians like frogs and salamanders lay eggs, but their eggs are not watertight. This means that they need to be laid in water or else their watery contents leak and the eggs dry up and die. This is why amphibians need to live near water for their species to survive. Birds lay eggs too, but their eggs are different, known as “amniotic" eggs. They have a hard exterior shell that keeps their watery contents safely inside and also protects them from predators and illness.   

From what we know, animals —reptiles more specifically— started laying eggs about 318 million years ago. So how did birds get in on laying eggs too?

Birds: Descendants of the Dinosaurs

Birds are direct descendants of dinosaurs… which makes them descendants of reptiles! The very first birds are thought to have appeared during the Jurassic Period, about 150 to 160 million years ago. At first, they looked more like small reptiles covered in feathers than the birds we see today. But over the course of time, these colourful Jurassic birds evolved into all kinds of different species that spread out across the world.

Now back to our chickens! Even if we aren’t exactly sure when chickens first appeared, it is thought that they became domesticated animals about 3,500 years ago in Southeast Asia. And get a load of this: chickens are some of the closest descendants of the ferocious Tyrannosaurus rex!  

An Undisputed Winner

Alright, recap! Chickens lay amniotic eggs, a trick they inherited from their reptilian ancestors. So that means that the egg came first, before the chicken! Feel free to share this tidbit with your family during your next meal, maybe as you enjoy an omelette together!

Nature is confronted with all sorts of challenges, but it ingeniously innovates and is always full of surprises! Come watch Animal Kingdom 3D: A Tale of Six Families at the IMAX®TELUS theatre and see for yourself!

Sources

• Benton, M. J., & Donoghue, P. C. J. (2007). Paleontological Evidence to Date the Tree of Life. Molecular Biology and Evolution, 24(1), 26‑53. https://doi.org/10.1093/molbev/msl150

• Ford, D. P., & Benson, R. B. J. (2020). The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae. Nature Ecology & Evolution, 4(1), Article 1. https://doi.org/10.1038/s41559-019-1047-3

• Magazine, S., & Gamillo, E. (s. d.). Researchers Pinpoint Date When Chickens Were First Domesticated. Smithsonian Magazine. Accessed May 8, 2023 at https://www.smithsonianmag.com/smart-news/researchers-pinpoint-date-when-chickens-were-first-domesticated-180980212/

• News, O. H. 10am-5pm M.-S. C. C. D. A. 1 W. S. S. N. 2010 A. P. +61 2 9320 6000 www australian museum C. © 2023 T. A. M. A. 85 407 224 698 V. M. (s. d.). The first birds. The Australian Museum. https://australian.museum/learn/dinosaurs/the-first-birds/australian.museum/learn/dinosaurs/the-first-birds/

• Romer, A. S. (1957). Origin of the Amniote Egg. The Scientific Monthly, 85(2), 57‑63.

• Starck, J. M., Stewart, J. R., & Blackburn, D. G. (2021). Phylogeny and evolutionary history of the amniote egg. Journal of Morphology, 282(7), 1080‑1122. https://doi.org/10.1002/jmor.21380