LUCA, the ‘Common Ancestor’ of All Living Things, Has Fascinated Us for Years. What Scientists Didn’t Know Is That It Was So Ancient

For centuries, scientists searched for the “missing link” almost obsessively, anxiously, as if finding it was the crowning achievement of human evolution.

However, the search proved to be useless, absurd, and meaningless. A complete waste of time.

Now, researchers are focused on finding LUCA, or the last universal common ancestor, and this search actually makes sense. In fact, a team of experts has just discovered an incredible piece of information: its “birthday.”

What is LUCA? LUCA represents more than just an organism. It’s a concept rooted in Charles Darwin’s evolutionary ideas and serves as the foundation of the vast phylogenetic tree that encompasses all life on Earth. LUCA marks the starting point of evolution and is thus responsible for all biodiversity.

This means that although LUCA isn’t the “first living being” to have existed, it dates far enough back in time to have given rise to all current life forms, including the simplest bacteria we know.

What do we know about LUCA? Well, the truth is that experts know very little. But for practical purposes, you can imagine LUCA as the “least common multiple” of terrestrial life. Scientists think LUCA was likely a single-celled organism that thrived in extreme conditions and was primitive but self-sufficient. They also believe that LUCA would have required an aquatic environment to survive and probably wasn’t the only living organism on the planet.

Can we learn more about LUCA? It’s challenging. First, researchers haven’t been able to find identifiable organic remains from 4 billion years ago, which is the time they estimate when LUCA would’ve existed. Even if scientists found remains, they might be so degraded that a detailed study would be impossible.

As a result, scientists have been gathering genes from various bacteria, archaea, animals, plants, and fungi to create a computational model of this common ancestor.

How experts found LUCA’s origins. Recently, an international team of researchers led by the University of Bristol traced back the “tree of life” to pinpoint the emergence of LUCA with unprecedented accuracy. They determined that LUCA appeared 4.2 billion years ago, just 400 million years after the formation of the Earth.

A big surprise. This discovery was surprising even to the researchers themselves. Sandra Álvarez-Carretero, one of the study's co-authors and a researcher at the School of Earth Sciences in Bristol, stated, “We did not expect LUCA to be so old, within just hundreds of millions of years of the Earth formation. However, our results fit with modern views on the habitability of early Earth.”

Moreover, this finding is significant because it helps explain the vast diversity between different ancient organisms, such as archaea and prokaryotes.

The surprises don't end there. Davide Pisani, who was also involved in the study, explained that “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.”

400 million years after Earth formed, the world was already as we know it: Millions of living things were struggling to survive to see another day. And that is fantastic.

Image | CDC| Camilo Jiménez

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