Probably the most debatable topic after the origin of life is the chicken-egg conundrum. Scientists are always in a fix when they have to answer which came first. This is very tricky but can be answered if we look back with scientific evidence.
To understand this, we need to find out what chicken is and how it evolved. We will have to take a step ahead and delve deeper into evolutionary biology to find out how the chickens evolved as domestic birds and the eggs alongside. Let us answer what is chicken first to begin this discussion.
We all know that birds are not the only species that lay eggs in the animal kingdom. There are many other species that use this method to give birth to a new generation. Chickens are one such species that lay eggs.
Chicken is considered a domestic fowl that we have brought closer to the human civilisations thousands of years ago. When humans started to shift their occupation from hunting and gathering to agriculture, we befriended many animals and settled down in particular favourable locations.
It is then that early humans saw the use of jungle fowls as potential egg machines. They could be domesticated and reared for meat and eggs. This was a good way to avoid risking life for hunting. Now, we can surely find a hint of where and when the chickens arrived in the world.
Well, this is not the case actually. We might have usurped the chicken population with our methods but the existence of chicken dates back way before our domestication.
The mating of two ancient fowls or proto chickens resulted in the genetic mutation and the formation of a modern chicken. It is a way of natural selection where the jungle fowls are considered the prehistoric father of the domestic chickens.
A question arises while discussing the evolution of chicken. What is proto chicken? Well, proto means primitive. It means this term is used to depict the primitive form of fowls as the ancestors of modern chicken. A jungle fowl differs in size from chickens. Their scientific name is Gallus gallus. On the other hand, the scientific name of chicken is Gallus gallus domesticus.
Most of the chicken species we rear originated from the red jungle fowl. Over years of domestication and breeding, we have developed this form of domesticated fowl or chicken. This is the evolution of chicken we need to understand before going to the discussion of eggs.
Let us discuss an egg from the perspective of chickens or fowls to find out the answer to the long-debated chicken-egg question.
Eggs are a vessel where an embryo develops after the mating of chickens. When a male and a female chicken mate, the union of the gametes results in the formation of an egg. Before the evolution of an egg to give birth to young ones, animals relied on a medium such as water for gamete union or fertilisation.
The development of eggs offered a better way to secure a union of gametes, the formation of a zygote and its secured growth. An egg is thus the development of a shell around a zygote inside a female chicken. Wait! Have we concluded the chicken-egg debate? Not yet!
An egg is formed when a hard covering of calcium carbonate forms on the embryo inside. All the chicken species we know follow the same evolutionary process and lay eggs to secure the young ones.
Here is some trivia to confuse us all. Eggs existed when the reptiles ruled the earth. In fact, we have found evidence that eggs were laid by vertebrate animals 370 million years ago. They are the ancestors of reptiles and birds. Does this mean the eggs are first? Well, it is an evolutionary feature that a major part of the reptilian and avian species follows. The process is the same, if you see the ‘how do chickens mate’ diagram, you will understand how eggs form inside a female chicken.
Egg or Chicken, Who is First?
We are still beating the bush and could not find a conclusion related to this topic. Well, here is something that will stop the itch in our brains.
Eggs form when a soft calcium carbonate shell is formed over the embryo. This shell hardens when it comes in contact with the atmosphere. It is formed with the help of a protein called the Ovocleidin-17 (OC-17). This protein is only found in the chicken species. It develops in the ovary of a female chicken and without it, no eggs will be able to sustain.
You will be surprised to know that OC-17 speeds up the process of shell formation in 24 hours. This is why we witness most chicken species lay eggs on a daily basis. This is why hens can develop eggs from scratch within a day.
Without this protein, it will be practically impossible to develop sustainable eggs. This protein is only found in chicken sources. From this, we can conclude that chickens are first, not eggs.
We can find eggs in reptiles and other avian species. If we debate on the fowl species only then it has to be the chicken first arriving. An egg will only form when two proto chickens mated and gave birth to the first chicken.
Similarly, an egg can only form when two chickens mate. Hence, there have to be two chickens involved to lay an egg. So, the chicken arrived earlier when compared to their eggs. Remember, we have considered the chicken eggs only and not the eggs of all species.