The chicken or the egg? We may finally know which came first

The complex web of life holds countless mysteries and its origins inspire endless queries. The question of which came first – the chicken or the egg – is a classic example.

This biological conundrum has been debated for centuries, perplexing philosophers, biologists, and curious minds alike.

But, we might finally be close an answer, thanks to an unexpected source – a single-celled species discovered just a mere four years ago.

The chicken or the egg?

The name of this remarkable species is Chromosphaera perkinsii. In an expedition around Hawaii in 2017, scientists discovered the species in marine sediments.

Surprisingly, the first signs of its presence on Earth trace back to over a billion years ago. This is well before the emergence of the first animals, let alone chickens or their eggs.

This long timeline of existence has allowed C. perkinsii to bear witness to some of the most monumental shifts in life as we know it.

Multicellular structures

A team of researchers at the University of Geneva (UNIGE), led by Professor Omaya Dudin, has been studying C. perkinsii. They have made a striking observation – this unicellular species forms multicellular structures that are eerily similar to animal embryos.

In the grand story of evolution, the transition from solitary, unicellular life forms (like yeast or bacteria) to complex, multicellular organisms (like animals) is a significant chapter.

This turns out to be a complex process, which starts with a single cell, the egg, and develops into complex beings. And believe it or not, this embryonic development process is remarkably similar across varied animal species.

The roots of multicellularity

Upon observing C. perkinsii, the UNIGE team made a startling discovery. Once these cells reach their maximum size, they divide without any further growth.

The result? Multicellular colonies. These colonies, which resemble a chicken egg structure, persist for a substantial part of their life cycle and bear a striking resemblance to the early stages of animal embryonic development.

So, does this mean that the researchers have stumbled onto the roots of multicellularity?

“Although C. perkinsii is a unicellular species, this behavior shows that multicellular coordination and differentiation processes are already present in the species, well before the first animals appeared on Earth,” said Professor Dudin.

Threads of evolution

Not only are the cells’ divisions and the three-dimensional structure they form similar to the early stages of animal embryonic development, but their genetic activity is in sync with it too.

In collaboration with Dr. John Burns at the Bigelow Laboratory for Ocean Sciences, the UNIGE team noticed intriguing similarities between the genetic activity within these colonies and that observed in animal embryos.

This implies that the complex genetic programs governing multicellular development, like those seen in the chicken and egg, may have already been in place over a billion years ago.

The chicken and egg mystery

Marine Olivetta, the first author of the study and a laboratory technician at the Department of Biochemistry in the UNIGE Faculty of Science, emphasized the significance of C. perkinsii.

“It’s fascinating, a species discovered very recently allows us to go back in time more than a billion years,” said Olivetta.

The profoundly interesting take-away from the study is that either the principle of embryonic development existed before animals, or multicellular development mechanisms evolved separately in C. perkinsii.

This discovery could shed a whole new light on a long-standing scientific debate concerning 600 million-year-old fossils that resemble embryos and could challenge certain traditional conceptions of multicellularity.

Chicken, egg, or C. perkinsii?

So, did the chicken come first, or the egg? According to the UNIGE team, it’s possible that the building blocks of female reproductive cells, or eggs, appeared long before chickens evolved.

Nature, therefore, could have possessed the genetic tools to create eggs long before chickens came along.

This unassuming, single-celled species might just have handed us a key piece of the evolutionary puzzle, improving our understanding of the origins of life.

New perspective on evolution

Life is a complex tapestry woven with the threads of countless organisms – each contributing to the multitude of species that inhabit our planet today.

The discovery of C. perkinsii and its fascinating developmental mechanisms challenges our conventional take on evolution, pushing us to rethink and reassess.

Who knows what other secrets are hidden within the depths of our vast oceans? Only time and relentless scientific pursuit will tell.

The study is published in the journal Nature.

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