People have been arguing for a long time about which came first, the chicken or the egg. You would need a chicken to lay the egg, but the chicken also comes from the egg. Luckily, the scientists know the answer to this riddle. To answer that, it would be good to know a little about the story behind the eggs and the chickens.
A lot of different animals lay eggs. An egg is an organic cell that is grown by an animal to carry a potential fertilized egg (zygote). You have probably heard that reptiles and birds lay eggs, but also monotremes lay eggs. They are the only mammals that lay eggs and feed their infants with milk. But there are also some animals you maybe haven’t thought about who also lay eggs. These are, for example, arthropods, vertebrates, and molluscs, but their eggs are covered with soft shells, and they have to lay them in water. Reptile, bird, and monotreme (for example, platypus) eggs are laid out on the side of the water. Their eggs are protected with a hardshell or flexible shell. Eggs are usually laid in nests, which are kept at a favourable temperature until they hatch. Some embryos even have an egg tooth. It’s a tooth that the embryo uses for breaking the eggshell. The largest egg is from a whale shark. The measurements are 30 cm x 14 cm x 9 cm. The largest bird egg is from an ostrich, it weighed 2.6 kg.
Domesticated chicken, also called Gallus domesticus, evolved from its wild ancestor, the red junglefowl. The male chicken is called a rooster, and the female one is called a hen. Chickens that are domesticated for their meat are called broilers. Chickens are the most common domestic animals. In 2018, the chicken population was around 24 billion. It is postulated that chickens were first domesticated around 10,000 years ago in Southeast Asia. DNA results also showed that the domesticated chicken diverged from its ancestors, maybe 58 000 years ago. Scientists have done DNA research to find out where the chickens originated, and the results show that the chickens evolved from red and green junglefowl. A large part of the evolution of chickens is also due to artificial selection.
Chickens and other birds evolved from small carnivorous dinosaurs. In 1860, palaeontologists discovered the first bird. It is called the Archaeopteryx. This fossil had feathers on its arms and tail. But it has teeth, birds that are living right now don’t have teeth. It also had a tail. Based on that discovery, this fossil had some similarities to birds, and some of them were similar to reptiles.
The first eggs came from amniotes, and they are more than millions of years old. The first animals had to lay their eggs in the water, because otherwise the sun would dry them up. The egg developed over time, and it now has three extra membranes inside. They are called the chorion, amnion, and allantois. Each membrane has a different function, but because of these layers, the egg had all-in-one life support.
When animals started to lay eggs, it opened up a new world for them. They were now able to also occupy the land. And also, with an improved egg, the animals had even more opportunities. We can’t say when it exactly happened because we simply don’t have egg fossils. Amniotes lived around 312 million years ago. Today’s mammals, reptiles, and birds all evolved from the first amniote. Now that we know that the first chicken evolved around 58 000 years ago, it is safe to say that the egg came first.
Sources:
https://en.wikipedia.org/wiki/Egg
https://www.discoverwildlife.com/animal-facts/birds/what-bird-laid-the-biggest-egg
https://en.wikipedia.org/wiki/Chicken
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873279/
https://evolution.berkeley.edu/what-are-evograms/the-origin-of-birds/
https://www.science.org.au/curious/earth-environment/which-came-first-chicken-or-egg