Scientists crack which came first - the chicken or the egg

Embryonic development may have existed before the evolution of animals, scientists say. Getty Images

The question of which came first, the chicken or the egg, has puzzled people for centuries. But scientists may have finally solved the mystery. Nature possessed the tools to create eggs long before it made chickens, according to a new study.

It is believed the first life forms to appear on Earth were composed of a single cell, evolving over time to become more complex. But the process of how that happened is not well understood.

To look into this, a team from the University of Geneva studied Chromosphaera perkinsii, a single-celled species that was discovered in 2017 in marine sediments around Hawaii. It separated from the animal evolutionary line more than a billion years ago, making it a good case study to probe the evolutionary process that led to multicellularity – or life forms made of multiple cells.

The scientists discovered that Chromosphaera perkinsii, once they reach their maximum size, divide without growing any further – forming multicellular colonies with a three-dimensional structure that looks similar to the early stages of animal embryonic development.

That means embryonic development might have existed before the evolution of animals, meaning the egg came before the chicken, they say.

These colonies persist for around a third of their life cycle and included at least two different cell types, which scientists describe as a “surprising phenomenon” for the type of organism. That suggests the process governing complex multicellular development was already present more than a billion years ago, the researchers said.

“It’s fascinating, a species discovered very recently allows us to go back in time more than a billion years,” said Marine Olivetta, a laboratory technician at the Department of Biochemistry in the Unige Faculty of Science and first author of the study.

She said the study demonstrates that either the principle of embryonic development existed before animals, or multicellular development mechanisms evolved separately in C. perkinsii.

‘‘Although C. perkinsii is a unicellular species, this behaviour shows that multicellular co-ordination and differentiation processes are already present in the species, well before the first animals appeared on Earth’’, said Omaya Dudin, who led the research.