The age-old question of whether the egg or the chicken came first has been surprisingly answered by researchers at the University of Geneva.
According to the study, published in “Nature”, the egg, or more precisely the genetic mechanisms which make embryonic development possible, preceded the appearance of the first animals.
A discovery born from the marine abysses
It all started in 2017, with the discovery of a single-celled organism called “Chromosphaera perkinsii” in marine sediments near Hawaii.
Neither animal nor plant, this protozoan has a fascinating characteristic: it can differentiate into two distinct types of cells, a behavior surprisingly close to that observed in the embryonic development of multicellular organisms.
“We were able to demonstrate that this organism, although unicellular, presents genetic mechanisms similar to those which allow embryonic development in animals”explains Omaya Dudin, professor in the biochemistry department at UNIGE. “This proves that these tools already existed about a billion years ago, long before the first animals set foot on this planet.”
The unclear origins of embryogenesis
Embryogenesis, the process allowing a single egg cell (zygote) to give rise to a complex organism, is today a pillar of the animal kingdom.
But this study calls into question the idea that this mechanism originated with animals, around 600 million years ago. On the contrary, researchers suggest that it appeared much earlier, in primitive unicellular organisms.
A major step forward in understanding evolution
The results obtained with “Chromosphaera perkinsii” show that the ability to coordinate cells and initiate multicellular development was already written in the genome of certain organisms a billion years ago.
These discoveries prompt us to reconsider the evolution of multicellular organisms. Primitive cell colonies, like those observed in “Chromosphaera perkinsii”, appear to have served as an experimental laboratory for the processes that would later lead to the appearance of the first animals.
The egg, a scientific metaphor?
Beyond the famous chicken-and-egg question, this research highlights a fascinating truth: the fundamental mechanisms of life, such as embryogenesis, existed long before complex life forms. The egg, as a metaphor for evolutionary potential, thus preceded the chicken, building a bridge between the distant past of unicellular organisms and the present of multicellular animals. A true revolution in our understanding of the history of life.
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