A recent discovery by scientists at the University of Geneva suggests that, long before the existence of animals or dinosaurs, nature was capable of creating an egg precursor.
The first forms of life on Earth were organisms composed of a single cell. In 2017, a single-cell organism dating back more than a billion years (Chromosphaera perkinsii) was discovered in seabed sediments near Hawaii. How multicellular organisms, such as animals and human beings, evolved after single-celled organisms is still a matter of considerable scientific uncertainty. All higher forms of life, including animals and human beings, also begin with a cell (the ovum), then divide and develop into complex structures: this is known as embryonic development, which also takes place inside an eggcel.
Swiss researchers have studied this billion-year-old single-cell organism and have published that it can divide and form multicellular structures. This behaviour suggests that a primitive form of multicellular development, such as that which occurs in an egg, existed billions of years ago, before the first animals appeared on Earth.
These discoveries imply that the ‘concept’ of an egg, or an embryonic structure in which an organism develops, was present in nature long before the existence of chickens and other birds. The egg can therefore be considered a universal principle of life.

But that still doesn’t give us an egg, just the processes that take place inside it. The evolution of the egg itself dates back 500 million years. Even then, fish laid their larvae in a protective sac containing an egg yolk.

This primitive egg allowed the offspring to develop outside the mother’s body. Hard-shelled eggs appeared later, when reptiles and then dinosaurs laid leathery eggs around 350 million years ago, before evolving into chalky, hard-shelled eggs. All this happened long before the appearance of birds, let alone chickens.

By contrast, the modern chicken (Gallus gallus domesticus) is relatively young. Genetic research shows that the domestic chicken was born around 3,600 years ago, probably as a result of cross-breeding and selection from the bankiva hen, an Asian bird species.

In the world of evolutionary biology, the situation is therefore relatively straightforward: eggs appeared long before the first chicken on Earth.