Scientists Find One Common Ancestor to All Present Living Beings
The origin and evolution of life on Earth, have been an intriguing topic for researchers worldwide. According to experts, the common ancestor of all living organisms, the Last Universal Common Ancestor (LUCA), emerged billions of years ago, Science Alert reported.
A recent study published in Nature explores the nature of this being and its impact on the evolution of the early earth system. LUCA was not the first form of life on Earth. It was from LUCA that all present living organisms have descended.
There is a lot of contention in the scientific community regarding LUCA's age. The earliest fossil evidence indicating life on Earth was around 3.4 billion years old. Certain studies though estimate the age to be close to the birth of Earth, 4.5 billion years ago.
Experts have contested the latter belief, citing the time it takes to establish the genetic code and DNA replication machinery in an organism.
For decades, scientists have been trying to understand the nature of LUCA to gain more ideas about how life evolved on Earth and reached the present state.
In the study published in Nature, a team of researchers applied a combination of scientific methods to reconstruct LUCA's genome and showcase how the gene construction shaped the organism's life.
The researchers acquired a sample of genomes from different groups of bacteria and archaea, as per the study. They were able to access a set of 700 genomes, curated for a separate 2022 study.
The genes were then separated into different families to understand their function concerning modern organisms. Thereafter, these families were used to formulate phylogenetic trees (sort of a family tree) to understand how different species went through evolution over time.
The research team built a set of 57 genes they found common in all 700 organisms in their study. According to the experts, if these genes were found in all the organisms, this implies that they have not changed much over the last few billion years.
The 57 genes were then used by the scientists to create a species tree, to show the Darwinian relationship of the different organisms, in the study. The phylogenetic trees and species trees were combined using modeling rates of gene duplication, gene transfer, and loss.
The combination allowed the researchers to estimate how likely it was for different gene families to be present in LUCA.
The reconstruction of LUCA's genomes helped researchers get a deeper understanding of the organism's metabolism, Science Alert reported. The analysis caused the experts to conclude that LUCA was a complex organism with a small genome, similar to modern bacteria and archaea.
The researchers found no evidence of a mechanism for processes like photosynthesis (which some bacteria use) or nitrogen fixation, a chemical process some modern bacteria and archaea use to stay alive, in LUCA, as per the study.
The study also focussed on estimating LUCA's age on Earth, Science Alert reported. To fulfill this objective, researchers used genes that they believed were duplicated before LUCA, along with information regarding fossils.
The typical process to create evolutionary timelines involves obtaining the phylogeny (evolutionary tree) of the concerned species, combining it with homologous (similar) genes, and tracing the common ancestor. In the next step, the experts would need to find a group of species that are distantly related to the concerned species, to find the root of phylogeny.
Applying this process for LUCA is difficult because, in this situation, the concerned species does not have any distantly related species, Science Alert reported. To overcome this drawback, the researchers in the study used paralogous genes, which in the past had been traced back to LUCA.
Paralogous genes are associated with each other, through the process of gene duplication. This phenomenon usually happens when a species gets split into two, each carrying with them, its copy of duplicated genes.
This slight adjustment, allowed the researchers to go through with the process, and they estimated LUCA to have roamed the planet around 4.2 billion years ago, as per the study. This finding implies that things like genetic code, protein translation, and life, must have evolved at a fast pace, and started right after the Earth was formed.