Which came first, the chicken or the egg? It depends on how you think about it, but the egg came first evolutionarily. Chickens were domesticated about 10,000 years ago and eggs evolved about 350 million years ago. This is one of those questions where the point is not the answer, but the thought process along the way. It is a good opportunity to learn about eggs and about chickens.
Hard shell eggs probably evolved about 350 million years ago, although it is difficult to know for sure because they don’t fossilize very well. Before that, eggs only had a very thin membrane. The first life on Earth was bacteria and it lived in the seas. Over hundreds of millions of years, it evolved into complex life and this lived in the oceans as well. Fish and other animals that live in the sea lay eggs that don’t have a hard shell. Fish eggs are contained inside a jelly-like substance that keeps the consistency of the eggs. Fish don’t need hard shells because of several reasons. The pressure of the water keeps the shape of the egg, the eggs are not in danger of drying out, they lay a lot of eggs and the survivability of single eggs is not a concern, they would use too much energy and resources making hard shells, and hard-shelled eggs would probably sink in the water. When organisms started coming out of the water, this began to change. A lot of amphibians come out of the water to live and feed, but they go back to the water to lay their eggs. They still lay soft eggs because they are in the water. However, that means they cannot move very far from the water.
Reptiles were probably the first lifeforms to evolve eggs with a shell. Their eggs have a leathery, rubbery covering that means they can be laid on land. The shell protects them and stops them from drying out. At the same time, the inside of the egg evolved as well. They developed three sections, called the chorion, amnion, and allantois. These contain all of the nutrients and fluids that the embryo will need. They also store all of the waste products that the embryo produces. They provide more cushioning and they help filter the oxygen that comes in through the shell. All of this meant that eggs could be laid anywhere and, so long as they were kept warm and safe, they would hatch into babies. All of this appears to have happened about 350 million years ago. The dinosaurs all laid eggs and birds, which are the descendants of dinosaurs, lay eggs.
So, what about chickens? The chickens that we breed today are vastly different to the first chickens that were domesticated. They have been bred to be bigger, to have more meat, or to lay more and bigger eggs. The first chickens were domesticated by humans roughly 10,000 years ago. These were red junglefowl, not the chickens that we know today. They probably started living near humans because they could get grain and other types of food from us. As with any other domesticated animal, the animal got things from us and we got things from the animal. In this case eggs, and much later, meat. Red jungle fowl are much smaller than chickens and they have a lot more color. After these first chickens, they were selectively bred to create more chicken like chickens. To make the first chicken, two junglefowl would have to be mated. There is no way of knowing when that was. There is no way to know when the junglefowl became the chicken that we know today. It could have been close to 10,000 years ago, or it might have been a lot closer. Archaeologists have found that the red junglefowl was probably domesticated somewhere in South East Asia and then it spread around the world over the next few thousand years. They have found a lot of chicken bones in places that grow rice and it appears that the chicken spread around the world along with rice farming. So, when the first chicken came out of its egg is unknown, but it would have been a junglefowl egg that it came out of, so, probably, the chicken came first.
If this is all correct, then eggs evolved almost 350 million years before the chicken evolved, so eggs came first. Chickens were then bred from red junglefowl, so the chicken came before the egg. And this is what I learned today.
Photo by Alison Burrell: https://www.pexels.com/photo/brown-hen-near-white-egg-on-nest-195226/
Sources
https://brainly.com/question/37958759
https://theconversation.com/curious-kids-what-came-first-the-chicken-or-the-egg-211917
https://www.science.org.au/curious/earth-environment/which-came-first-chicken-or-egg
https://en.wikipedia.org/wiki/Fetal_membranes
https://en.wikipedia.org/wiki/Red_junglefowl
https://www.science.org/content/article/how-wild-jungle-fowl-became-chicken