Illustration showing how LUCA could have been attacked by a virus
scientific graphic design
The organisms that gave rise to all life on Earth may have evolved much earlier than once thought, just a few hundred million years after the planet formed, and may have been more sophisticated than previous estimates suggest.
The DNA inside every organism alive today is Escherichia coli There are many similarities with the blue whale, suggesting that they can all be traced back to the last universal common ancestor, LUCA, billions of years ago. There has been a lot of effort to understand LUCA, but now a study that takes a broader approach has produced some surprising results.
“What we’ve tried to do is bring together people from different disciplines to get a holistic understanding of when LUCA existed and what its biology was,” he said. Philip Donohue From the University of Bristol, UK.
Genes found today in all major areas of life could have been passed down uninterrupted from LUCA, allowing us to figure out what genes our ancient ancestors had. By looking at how these genes changed over time, we can estimate when LUCA lived.
In reality, this is much trickier than it sounds, because genes are lost, gained, and swapped between branches. Donohue says the team built complex models that take this into account to figure out which genes are present in LUCA. “We’ve created an organism that is much more sophisticated than many people have claimed in the past,” he says.
The researchers estimate that as many as 2,600 protein-coding genes could have originated from LUCA, compared with some previous estimates of just 80. The team also concluded that LUCA lived around 4.2 billion years ago—much earlier than other estimates and surprisingly close to the time when Earth formed, 4.5 billion years ago. “This suggests that evolving life may have been simpler than people previously assumed, because it happened so early,” Donoghue says.
This earlier date is partly due to what the team says is an improved methodology, but unlike others, the researchers do not assume that LUCA could only have existed after a late bombardment, when Earth was bombarded by space debris, possibly wiping out any budding lifeforms. That period has been estimated at 3.8 billion years ago, based on rocks brought back from the moon, but there is a lot of uncertainty about that figure, Donoghue says.
The researchers believe that LUCA most likely lived on the ocean surface because its reconstruction contained genes that protect it from UV damage. Other genes suggest that LUCA fed on hydrogen, which is consistent with previous studies. The team speculates that LUCA may have been part of some other kind of primordial cell ecosystem that died out. “I think it’s extremely naive to think that LUCA could have existed on its own,” Donoghue says.
“I find this fascinating from an evolutionary perspective,” he said. Greg Fournier From the Massachusetts Institute of Technology. “LUCA is not the beginning of the story of life, but rather the last shared ancestral state that can be traced back using genomic data.”
The results also suggest that LUCA had a primitive version of a bacterial defense system known as CRISPR to fight viruses. “Even 4.2 billion years ago, our earliest ancestors were fighting viruses,” the team member said. Edmund MoodyAlso at the University of Bristol.
Looking back deep into the past is fraught with uncertainty, and Donohue is the first to admit that his team may have missed the mark. “We’re almost certainly all wrong,” he says. “What we’re trying to do is push the boundaries and make the first attempt to integrate all the relevant evidence.”
“It won’t be the last word,” he says. “It won’t be the last word on this topic. But I think it’s a good start.”
Patrick Pottere Researchers at the Pasteur Institute in Paris, France, who coined the term LUCA, also don’t think the organism lived in isolation. “But the idea that LUCA lived before the 3.9 billion-year bombardment seems completely unrealistic to me,” says Porter. “I’m sure there are some flaws in their strategy for determining the age and genetic content of LUCA.”
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