LUCA: Meet your oldest ancestor

When we think about ancestry, most of us picture family trees that stretch back a few hundred years, or haplogroups, that can stretch tens of thousands. But what if we zoomed out - way out - to 4 billion years ago? Scientists have identified a fascinating figure at the base of life’s tree: LUCA, the Last Universal Common Ancestor. LUCA isn’t a single creature, or even a specific species, but rather a hypothetical organism that links all life forms, from humans like you or I, through to the tiniest microbes, through a shared genetic legacy.

Luca’s World

A lot has been hypothesised about LUCA’s daily life in the early days of existence. It likely thrived in extreme environments, such as the hydrothermal vents on the ocean floor, where magma and seawater collide to create toxic plumes. These vents would have offered the hydrogen gas that LUCA used for energy, a necessity in a world that was (as yet) devoid of oxygen. Its genetic traits suggest that it was an extremophile, similar to some modern bacteria and archaea that still live in these conditions today.

By analysing thousands of genomes from modern microbes, scientists have identified 355 gene families shared across bacteria and archaea, pointing to Luca as their source. These genes include those for basic survival, like making proteins and maintaining a cell membrane, forming a molecular blueprint for life as we know it.

A Debate on Origins

While many scientists agree that LUCA lived near hydrothermal vents, others argue that life’s origins may lie elsewhere. Some point to “warm little ponds” on land, where sunlight and chemical reactions might have sparked the earliest life forms. It’s possible that life began in multiple places, with global events - like asteroid bombardments - reshaping the planet and concentrating life into environments like deep-sea vents.

Why LUCA Matters

LUCA’s story is more than a scientific curiosity - it’s a reminder that all life is interconnected. Every creature on Earth, from ancient microbes to modern humans, carries a piece of this ancient organism in its DNA. By studying LUCA, scientists aren’t just uncovering the origins of life; they’re also piecing together how life adapted, thrived, and diversified into the millions of species we see today.

Learning about LUCA invites us to reflect on our shared biological heritage, offering a profound perspective on how far life has come since its earliest days in Earth’s most extreme environments. Whether life began in deep-sea vents, sunlit ponds, or elsewhere, LUCA reminds us that our roots are deeper - and more connected - than we might ever imagine.