The common ancestor of all living things today is deciphered

2024-08-27 15:32:12

“The Bush of the Living”, description from the project “The Great Tree of Life” by Laetoli Production ( LAETOLI PRODUCTION/SAMBA SOUSSOKO

From trees to humans, from elephants to the smallest bacteria, all living things today have a common ancestor, a small cell that the scientific community called LUCA, from last universal common father (“the last universal ancestor”).

But LUCA is not the origin of life. It is the oldest species that we can go back to, by analyzing the genes of current living organisms. A great challenge for scientists, genealogists of these lives. An international team proposes a reconstruction of the LUCA genome, and a new dating, work published in July in the journal Science Nature Ecology and Evolution.

“According to our estimation, this LUCA is a complex organism”says Edmund Moody, researcher in evolutionary biology at the Paleobiology Group at the University of Bristol, United Kingdom, and first author of the research. Your genome will have plans for 2,600 proteins. The number is higher than previous estimates.

Common core

To reach this number, the authors first created a database from the genomes of prokaryotes, the unicellular organisms of the modern world, such as bacteria. Then they used a new algorithm. “It allows, for each gene family, to establish a probability that is present in the LUCA gene”explains Tom Williams, co-author, professor at the University of Bristol.

“If we have a concept of phylogeny [la généalogie] species, this method makes it possible to reconstruct the evolutionary situation for each species.specified Vincent Daubin, CNRS research director at the Laboratory of Biometrics and Evolutionary Biology, in Villeurbanne (Rhône), who worked on the method but did not participate in the research.

Imagine a tree. It’s LUCA the base of your trunk. And all species currently grow leaves. The researchers also made a tree for each gene to understand its history. And they removed such genes from current prokaryotes already present in LUCA.

Genes are passed down to offspring, from roots to leaves. But they can also spread between species, outside, between the branches of the tree. “This new method makes it possible to detect horizontal movement”, continued phylogeneticist.

“Uncertainties”

“These horizontal transfers are difficult to detect, especially when they are old. The risk is to overestimate the number of genes present in LUCA”nuance Purificacion Lopez-Garcia, research director at the Laboratory of Ecology, Systematics and Evolution at Paris-Saclay University. The scientist pointed out “great uncertainties” of research.