Researchers have revealed that the last common factor among humans, insects and algae is Luca.

The Last Universal Common Ancestor of every living thing on Earth was subject to a study by evolutionary biologists, who have now published a detailed genetic profile of the organism, writes Joseph Dussault for The Christian Science Monitor.

Archaea Bacteria Eukaryotes LUCA
Image source: Wikimedia Commons

Luca the subject of new study

A study into the ancient precursor was published Monday in Nature Microbiology, providing an insight into how and where the organism could have lived.

On Earth there are three basic kinds of living organisms: bacteria, eukaryotes and archaea. Every plant and animal is a eukaryote, while bacteria and archaea are single-celled, asexual organisms that do not have a nucleus or organelles, but do possess genetic and biochemical backgrounds of their own.

Scientists believe that all three groups share an ancestor in Luca, a single-celled organism that was alive approximately 4 billion years ago. Researchers previously believed that Luca diverged into archaea and bacteria, while eukaryotes arrived later.

Last Universal Common Ancestor may have lived in deep-sea vents

However further study into the physiology and habitat of Luca has now been carried out by a group of evolutionary biologists. The team was led by William Martin of Heinrich Heine University in Germany, and started work on a genetic profile of Luca.

The team were able to identify 355 protein-coding genes in both bacteria and archaea that are likely to have originated in Luca. One of the genes is only found in extremophile microbes and codes for an enzyme known as reverse gyrase.

“I was flabbergasted at the result,” Martin told The New York Times. “I couldn’t believe it.”

The genes found by the team suggest that Luca lived in hot vents deep under the world’s oceans, and would have metabolized hydrogen gas for energy. According to some scientists, life itself would have originated in a similar environment.

How did life on Earth begin?

Martin has now argued that far from being just a common ancestor, Luca may in fact be one of the first organisms to have lived on Earth. This feeds into another puzzling question for scientists: how did life suddenly develop from non-living organic materials?

One school of thought suggests that a “primordial soup” of basic chemicals and warm water was responsible for the first living organisms, while researchers from Cornell University suggested that life may have come about in clay.

According to John Sutherland, a chemist at the University of Cambridge, ultraviolet light is an essential energy source for the chemical reactions needed to spark the creation of life. Given that ultraviolet light comes from the sun, life must have begun in pools on land.

Sutherland says that Luca may have lived in deep-sea vents, but life on Earth probably started far earlier.

“We didn’t set out with a preferred scenario,” Sutherland told The New York Times. “We deduced the scenario from the chemistry.”

Scientists now need to conduct further research in order to get to the bottom of the mystery. The branches of the trees of life are complicated to unravel and it is not yet clear whether Luca is the Last Universal Common Ancestor or one of the oldest organisms on the planet.

The subject continues to fascinate scientists and observers alike, and the latest findings are a step towards unpacking the mystery of how life on Earth began.