The last universal common ancestor (LUCA) is the hypothesized common ancestor from which all modern cellular life, from single celled organisms like bacteria to the gigantic redwood trees — as well as us humans — descend. As such, our understanding of LUCA impacts our understanding of the early evolution of life on Earth.
Probabilistic estimates of metabolic networks from modern life that were present in LUCA. Image credit: Moody et al., doi: 10.1038/s41559-024-02461-1.
LUCA is the node on the tree of life from which the fundamental prokaryotic domains (Archaea and Bacteria) diverge.
Modern life evolved from LUCA from various different sources: the same amino acids used to build proteins in all cellular organisms, the shared energy currency (ATP), the presence of cellular machinery like the ribosome and others associated with making proteins from the information stored in DNA, and even the fact that all cellular life uses DNA itself as a way of storing information.
In new research, University of Bristol scientist Edmund Moody and his colleagues compared all the genes in the genomes of living species, counting the mutations that have occurred within their sequences over time since they shared an ancestor in LUCA.
The time of separation of some species is known from the fossil record and so the team used a genetic equivalent of the familiar equation used to calculate speed in physics to work out when LUCA existed, arriving at the answer of 4.2 billion years ago — just 400 million years after the formation of Earth and our Solar System.
“The evolutionary history of genes is complicated by their exchange between lineages,” Dr. Moody said.
“We have to use complex evolutionary models to reconcile the evolutionary history of genes with the genealogy of species.”
“We did not expect LUCA to be so old, within just hundreds of millions of years of Earth formation,” said Dr. Sandra Álvarez-Carretero, also from the University of Bristol.
“However, our results fit with modern views on the habitability of early Earth.”
The study authors also worked out the biology of LUCA by modeling the physiological characteristics of living species back through the genealogy of life to LUCA.
“One of the real advantages here is applying the gene-tree species-tree reconciliation approach to such a diverse dataset representing the primary domains of life Archaea and Bacteria,” said University of Bristol’s Dr. Tom Williams.
“This allows us to say with some confidence and assess that level of confidence on how LUCA lived.”
“Our study showed that LUCA was a complex organism, not too different from modern prokaryotes, but what is really interesting is that it’s clear it possessed an early immune system, showing that even by 4.2 billion years ago, our ancestor was engaging in an arms race with viruses,” said University of Bristol’s Professor Davide Pisani.
“It’s clear that LUCA was exploiting and changing its environment, but it is unlikely to have lived alone,” said Dr. Tim Lenton, a researcher at the University of Exeter.
“Its waste would have been food for other microbes, like methanogens, that would have helped to create a recycling ecosystem.”
“The findings and methods employed in this work will also inform future studies that look in more detail into the subsequent evolution of prokaryotes in light of Earth history, including the lesser studied Archaea with their methanogenic representatives,” said Professor Anja Spang, a researcher at the Royal Netherlands Institute for Sea Research.
“Our work draws together data and methods from multiple disciplines, revealing insights into early Earth and life that could not be achieved by any one discipline alone,” said University of Bristol’s Professor Philip Donoghue.
“It also demonstrates just how quickly an ecosystem was established on early Earth.”
“This suggests that life may be flourishing on Earth-like biospheres elsewhere in the Universe.”
The research is described in a paper published today in the journal Nature Ecology & Evolution.
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E.R.R. Moody et al. The nature of the last universal common ancestor and its impact on the early Earth system. Nat Ecol Evol, published online July 12, 2024; doi: 10.1038/s41559-024-02461-1
This article is a version of a press-release provided by the University of Bristol.