For decades, scientists have believed that LUCA (Last Universal Common Ancestor) was the starting point of all life on Earth. This single-celled organism, thought to have lived around 4.2 billion years ago, is considered the root of the evolutionary tree from which bacteria, plants, animals, and humans evolved.
However, a groundbreaking new study published in Cell Genomics suggests that LUCA was not the beginning of life. Instead, it was the survivor of a much older and more complex biological world, inheriting essential genetic machinery from long-lost ancestors known as “pre-LUCA” organisms.
Unlocking Life’s Earliest Genetic Roots
Because fossils from four billion years ago do not exist, researchers from MIT and Oberlin College turned to genetic clues embedded in all living organisms today. They focused on “universal paralogs”—rare duplicated genes that appear in every branch of life.
These duplicated genes must have existed before the major branches of life diverged, meaning they predate LUCA. Scientists describe them as the buried roots of the evolutionary tree, revealing that a diverse and productive ecosystem of primitive cells existed before our universal ancestor emerged.
According to the researchers, this ancient world likely consisted of early cells exchanging DNA and developing complex biological systems, long before modern life took shape.
A Surprisingly Complex Beginning of Life
The study also found that these ancient genes were not minor or redundant. Instead, they powered some of the most fundamental processes of life, including:
- Protein factories: Ancient enzymes responsible for linking amino acids and building proteins
- Cell security systems: Proteins that helped maintain and protect cell membranes
The researchers explained that “genetics is written by the victors”—many early life forms went extinct, but the most efficient genetic systems survived and became the foundation of all life today.
Rewriting the Story of Life on Earth
This discovery suggests that the genetic code and biological complexity did not emerge suddenly with LUCA, but developed gradually in an even earlier era of primitive organisms. It paints a picture of life’s origin as far older, more sophisticated, and more evolutionary competitive than scientists previously believed.
The findings could reshape how researchers study the origin of life on Earth and even guide the search for life on other planets.