File this under we-are-all-connected: three billion years ago, life on Earth may have been a global mega-organism called LUCA, from which all living things today are descended. Can we get an artist’s rending of this colossal being? New Scientist writes:
ONCE upon a time, 3 billion years ago, there lived a single organism called LUCA. It was enormous: a mega-organism like none seen since, it filled the planet’s oceans before splitting into three and giving birth to the ancestors of all living things on Earth today.
This strange picture is emerging from efforts to pin down the last universal common ancestor – not the first life that emerged on Earth but the life form that gave rise to all others.
The latest results suggest LUCA was the result of early life’s fight to survive, attempts at which turned the ocean into a global genetic swap shop for hundreds of millions of years. Cells struggling to survive on their own exchanged useful parts with each other without competition – effectively creating a global mega-organism.
It was around 2.9 billion years ago that LUCA split into the three domains of life: the single-celled bacteria and archaea, and the more complex eukaryotes that gave rise to animals and plants (see timeline). It’s hard to know what happened before the split. Hardly any fossil evidence remains from this time, and any genes that date that far back are likely to have mutated beyond recognition.
That isn’t an insuperable obstacle to painting LUCA’s portrait, says Gustavo Caetano-Anollés of the University of Illinois at Urbana-Champaign. While the sequence of genes changes quickly, the three-dimensional structure of the proteins they code for is more resistant to the test of time. So if all organisms today make a protein with the same overall structure, he says, it’s a good bet that the structure was present in LUCA.