Which came first, the egg or the chicken? A team of scientists has introduced a fresh theory that may finally solve the age-old debate.
Before adulthood brought worries like taxes, bills, and life choices, our biggest dilemmas were simpler—like what to have for dinner, when the next playdate was, or the classic question: chicken or egg?
Now, researchers from the University of Bristol’s School of Earth Sciences have tackled this question head-on.
Some believe eggs came first, laid by the dinosaur ancestors of modern chickens, while others argue that the chicken came first, laying eggs thereafter. A study published in Nature Ecology & Evolution took a deep dive into the debate by examining 51 fossil species and 29 living ones. They grouped them into two categories: oviparous (egg-layers) and viviparous (those giving live birth, like humans).
The results showed that early reptilian ancestors of chickens were viviparous—they gave birth to live young instead of laying eggs.
Although both the University of Bristol and Nanjing University teams acknowledged that hard-shelled eggs were a revolutionary development for survival, this research offers a new perspective.
The team suggests that extended embryo retention—where a mother carries her young before giving birth—was a protective advantage. In other words, giving birth to live chickens may have been safer than laying eggs.
Professor Michael Benton of the University of Bristol explained: “Before amniotes, early tetrapods were largely amphibious. They needed to live near water to feed and breed, similar to modern frogs and salamanders. When amniotes emerged around 320 million years ago, they evolved waterproof skin and other mechanisms to break free from a life tied to water, with the amniotic egg playing a crucial role.”
He added, “Our research, along with others in recent years, has essentially thrown out the textbook model of the ‘reptile egg.'”
Project leader Professor Baoyu Jiang noted, “This traditional view has been challenged. Biologists have observed that many lizards and snakes can switch between laying eggs and giving live birth. Live-bearing lizards, in particular, can revert to laying eggs more easily than previously thought.”
So, the debate may not be fully settled, but it seems we’re getting closer to cracking the mystery. Could the chicken have come first after all?
What’s your take?