Have scientists solved the chicken or egg problem?

Scientists have made a discovery that may finally answer the age-old question: Which came first, the chicken or the egg? A recent study from the University of Geneva suggests that the egg came first, as reported by the New York Post. The findings, published in the journal Nature, indicate that developmental processes similar to those of animal embryos existed long before the first animals appeared around 800 million years ago.

The research centers on a unicellular organism called Chromosphaera Perkinsii, discovered in marine sediments near Hawaii in 2017. This organism, which has existed for over a billion years, shows that structures akin to embryos existed before the emergence of multicellular animals. "It's fascinating, a species discovered very recently allows us to go back in time more than a billion years," said biochemist Marine Olivetta from the University of Geneva, who led the study.

Upon reaching its maximum size, Chromosphaera Perkinsii divides into clusters of smaller cells, forming structures with distinct types of cells—a behavior typically associated with multicellular organisms. The cell cluster formed by this microbe closely resembles an animal embryo in its earliest stage, known as a blastula. This resemblance has led scientists to propose that it may serve as a model for understanding the origins of multicellularity, according to Science Times.

Researchers were surprised to find that these multicellular colonies persist for approximately one-third of the organism's life cycle, a phenomenon they define as "surprising" for this type of organism, according to The Independent. "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," explained Omaya Dudin, a researcher from the Swiss Federal Institute of Technology.

Unicellular life forms like yeast or some bacteria appeared on the planet long before multicellular organisms like animals, which developed from a single egg cell into complex beings, according to Delfi Mokslas. The embryo development process in animals follows very particular stages known to be remarkably similar between animal species. Scientists have long suspected that the processes of embryo development and multicellularity evolved much earlier, long before animals appeared.

One of the great unresolved enigmas in biology is how evolution progressed from unicellular organisms to multicellular ones, and exactly how this transition occurred is still very poorly understood, according to The Independent.

These multicellular colonies comprise at least two distinct types of cells, which is considered extraordinary for a unicellular life form. "Chromosphaera Perkinsii exhibits multicellular coordination and differentiation processes, phenomena previously thought exclusive to animals," explained Dudin, as reported by Science Times. These findings challenge previous assumptions about the timeline of evolutionary development and suggest that the genetic programs allowing complex multicellular development could have existed much earlier than previously thought.

This article was written in collaboration with generative AI company Alchemiq