A team of scientists has shown that ctenophores, jellyfish-like creatures, are the oldest relatives of today’s wide range of animals, placing that critical moment in evolution more than 700 million years ago, in a study published Wednesday in Nature. got to know.
The research, led by the Monterey Bay Aquarium Research Institute (MBARI, USA), aimed to put an end to a debate that has divided the scientific community for more than a century, as another hypothesis suggested that evolution was caused by Porifera. It started from Also known as sea sponge.
For this work, the experts analyzed clusters of genes that are always found together on the same chromosome, whether in humans, rodents, molluscs or corals, until they discovered that ctenophores are similar to “all other animals”. There are so-called “sister groups”. , , they reveal in a statement.
This discovery of genetic links will help, they emphasize, to understand how key features of animal anatomy have evolved over time, such as the nervous or digestive systems.
“We have developed a new way to look as far back as possible for the origins of animal life. We can go back almost a billion years and look at the evolution of animals,” says Darin Schultz, MBARI alumnus and now researcher at the University of Vienna (Austria). turned to genetics to get the clearest evidence for the earliest events.”
Experts recall that while all genes are arranged in sequences on chromosomes and their location can change over time, changes in the links between genes on a particular chromosome “are rare and largely irreversible.”
So far, however, researchers have focused only on similarities in “sequencing of individual genes” to address questions about “old animal relationships”.
Instead, Schultz and his team looked at relationships between genes on specific chromosomes, which tend to persist over time.
Thus, he identified patterns now present in a wide variety of animals, links that he traced back to the “starting point of evolution”.
Using these data, the researchers found “strong evidence” showing that ctenophores represent “a unique lineage” whose ancestors “split before the common ancestor of all other animals.”
This event can be described, they specify, as “a genetic fork” that occurred “hundreds of millions of years” in the “path of evolution”.
“A single-celled being, the progenitor of all animals, walked that road with two of its offspring. One of them, which would become today’s ctenophores, took one path and as it evolved, the genes on its chromosomes remained in a specific order and changed little.
In contrast, the “second son” followed the other path, until he “became the sea sponge and all the other animals as we know them today.”
