In “The science ticket of the weekend”, we are looking for the oldest animal lineage, a billion years ago, therefore, ours. We thought the sponge was our first cousin. But no, our first cousin looks like a gelatinous jellyfish.
Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, turn it up time today of almost a billion years, with a scientific discovery that tells another story of our evolution.
franceinfo: A team of researchers has just discovered the first animal that separated from our branch, in the tree of life?
Mathilde Fontez: Yes, researchers have a name for this species, they call it the “sister of all animals”. We can also say that it is our first cousin – like the chimpanzee is one of our last cousins. It is a separation in the tree of life, which is much studied, because it marked a fracture, very early, in evolution.
800 million years ago, when multi-celled organisms appeared, they separated: on the one hand, evolved all animals, including us. And on the other, very different animals, like sponges. And precisely, until then, we thought that it was an ancestor of the sponge that had marked this separation. That she formed the oldest line.
But today, an international team, led by Darrin Schultz, from the University of Vienna shows that no, it’s not the sponge! This first cousin is an animal called ctenophore: it looks a bit like a gelatinous jellyfish, they have fine tentacles, called combs, with which they move.
How did the researchers find out about this? Go back in time to this point?
by genetic studies. There had already been clues for ten years. These ctenophores had shown even more distant genetics than that of the sponges of other animals. This had sown doubt. But biologically, it was really hard to believe: sponges are ideal candidates as an ultra-primitive species, because they are very simple organisms: they don’t have muscle cells, they don’t have nerve cells.
While the ctenophores, nothing to do: they are predators, rather complex animals. It was logical to think that they had evolved afterwards. What makes the difference today is a new genetic approach: a more global study of genes, their distribution on the chromosomes. All this tends to prove that the ctenophores were the first to split from the main line.
Does that make it the oldest animal lineage?
Yes ! And it rewrites the tree of life. For these ctenophores to be so old, the neuronal cells, for example, must have formed earlier: 100 million years earlier than previously thought, according to the researchers. This first separation tells another story of our own evolution.