New understanding suggests LUCA, the last common ancestor of all life, emerged earlier than previously believed

The organisms that gave rise to all life on Earth evolved much earlier than previously thought – just a few hundred million years after Earth formed – and may have been more sophisticated than previous assessments had suggested.

The DNA of all living organisms today is E. coli There are many similarities in the evolution leading up to the blue whale, suggesting that we can trace our origins back to a universal common ancestor, LUCA, billions of years ago. While many efforts have been made to understand LUCA, studies taking a broader approach have revealed surprising results.

“What we're trying to do is bring together representatives from different disciplines to develop a comprehensive understanding of when LUCA existed and what its biological characteristics were,” he said. Philip Donahue At the University of Bristol, UK.

Genes that are currently present in all major lineages of life may have been passed down uninterrupted from LUCA, which could help us understand what genes our ancient ancestors had. By studying how these genes changed over time, we should be able to estimate when LUCA lived.

In reality, this is a lot more complicated than it sounds, as genes are lost, gained, and swapped between branches. Donohue says the team created a complex model that took this into account, to work out which genes were present in LUCA. “We've found a much more sophisticated organism than many have previously claimed,” he says.

The researchers estimate that 2,600 protein-coding genes come from LUCA, up from previous estimates of as few as 80. The team also concludes that LUCA lived around 4.2 billion years ago, much older than other estimates and surprisingly close to the formation of Earth 4.5 billion years ago. “This suggests that the evolution of life may have been simpler than previously claimed, because evolution happened so quickly,” Donohue says.

The earlier date is largely due to the team's improved methodology, but also because, unlike others, they don't assume that LUCA could have existed only after the Late Heavy Bombardment, when Earth was hit so hard by space debris that any new life that emerged could have been wiped out. Based on rocks returned from the Moon, the period has been put at 3.8 billion years ago, but there's a lot of uncertainty around that number, Donohue says.

Their reconstruction suggests that LUCA had genes that protected it from ultraviolet damage, which leads them to believe that it likely lived on the ocean's surface. Other genes suggest that LUCA fed on hydrogen, which is consistent with previous findings. The team speculates that LUCA may have been part of an ecosystem with other types of primitive cells that are now extinct. “I think it's extremely naive to think that LUCA existed on its own,” Donohue says.

“I think this is compelling from an evolutionary perspective.” Greg Fournier “LUCA is not the beginning of the story of life, but merely the state of the last common ancestor that we can trace back to using genomic data,” say researchers from the Massachusetts Institute of Technology.

The results also suggest that LUCA had a primitive version of the bacterial defense system known as CRISPR to fight viruses. “Even 4.2 billion years ago, our earliest ancestors were fighting viruses,” the team members say. Edmund Moodyalso at the University of Bristol.

Peering into the distant past is fraught with uncertainty, and Donohue is the first to admit that his team may have missed the mark. “We've almost certainly got it all wrong,” he says. “What we're trying to do is push the envelope and create the first attempt to synthesize all of the relevant evidence.”

“This won't be the last word,” he said, “and it won't be our last word on this subject, but we think it's a good start.”

Patrick Forter Researchers at the Institut Pasteur in Paris, France, who coined the term LUCA, also believe that the organism did not live in isolation. “But the claim that LUCA lived before the Late Heavy Bombardment 3.9 billion years ago seems to me completely unrealistic,” says Forterre. “I'm convinced that their strategy for determining the age and gene content of LUCA has several flaws.”