The Roots
Every biology textbook draws the tree of life the same way. At the base, a single trunk: LUCA, the Last Universal Common Ancestor, the organism from which every living thing on Earth descends. Bacteria, archaea, eukaryotes — all branches from that one trunk, roughly four billion years ago.
LUCA is where evolutionary biology begins. It is the deepest node we can reach with phylogenetic methods, the furthest point to which we can trace the branching of genomes. Below LUCA, the methods run out. The fossil record doesn't extend that far. The molecular clock loses its calibration. We hit bedrock.
Except the bedrock has fossils in it.
The Genes That Were Already Old
In a perspective published in Cell Genomics, Aaron Goldman (Oberlin College), Greg Fournier (MIT), and Betül Kaçar (University of Wisconsin–Madison) draw attention to a class of genes they call universal paralogs — and argue that these genes are our only window into the period of evolution before LUCA existed.
A paralog is a gene that has been duplicated within a genome. Humans carry eight hemoglobin genes, for example, all descended from a single ancestral globin gene that was copied roughly 800 million years ago. Each copy drifted, specialised, found its own niche. This is ordinary evolutionary business.
Universal paralogs are not ordinary. These are gene families that appear in at least two copies in the genomes of virtually every living organism on Earth — bacteria, archaea, and eukaryotes alike. Their ubiquity means one thing: the original duplication happened before the tree of life branched. Before LUCA. These genes were already doubled, already diverging, already specialised, when the organism we call the ancestor of all life was itself still young.
LUCA inherited them.
The First Two Trades
Here is what strikes me most. When Goldman and colleagues reviewed every known universal paralog, they found that every single one falls into one of two functional categories: making proteins or moving molecules across membranes.
These are not random functions. These are the two most fundamental things a cell does. Translation — reading genetic instructions and assembling proteins — is the core act of biological information processing. Membrane transport — selectively moving molecules in and out — is the core act of biological boundary maintenance. One builds the machinery. The other defines the self.
Before LUCA, before the trunk of the tree of life, life had already specialised in exactly these two directions. The first two trades.
A Functioning Ghost
This is not merely inference. Goldman's lab at Oberlin has reconstructed one of these ancient proteins — a universal paralog involved in inserting newly made proteins into cell membranes. Using standard methods of ancestral sequence reconstruction, they built the protein that would have existed before the duplication, before LUCA, before the tree.
It works. The reconstructed protein still attaches to membranes. It still interacts with the ribosome, the molecular machine that builds proteins. A ghost from before the beginning of recorded evolution, and it is functional.
"The history of these universal paralogs," says Fournier, "is the only information we will ever have about these earliest cellular lineages, and so we need to carefully extract as much knowledge as we can from them."
Only a handful of universal paralogs are currently known. Many more may exist but remain undetectable — obscured by billions of years of sequence divergence, gene loss, and horizontal gene transfer. The signal degrades. The palimpsest fades. But what remains is legible, and what it says is: the starting line was already behind us.
The Thread
This is the tenth piece in what has become a recurring observation across very different fields. The 3D genome was organised before the embryo "woke up." The episodic and semantic memory systems turned out to share the same neural room. The genetic code turned out to be polysemous. Ice Age marks turned out to encode structured information 35,000 years before writing.
Every time we look more carefully at a boundary — between order and chaos, between origin and inheritance, between the first chapter and what came before — the boundary dissolves. There was always something there already.
LUCA is the trunk. But the roots go deeper. And they were already doing the only two things that matter: building, and deciding what gets in.
Source: Goldman, A.D., Fournier, G.P. & Kaçar, B. (2026). Universal paralogs provide a window into evolution before the last universal common ancestor. Cell Genomics. DOI: 10.1016/j.xgen.2026.101140