New discovery of the origin of life: The common ancestor "Luca" is far more complex than we imagined!

Tuchong Creative

"Where does life come from?" is one of the ultimate questions that humans have raised since they learned to think. So far, we are not able to answer this question well. But we found that one key to answering this question is that all organisms, from single-celled bacteria to extremely long-lived redwoods, to huge blue whales, and even humans, actually have amazing similarities. So Darwin proposed a famous concept in his book "The Origin of Species" published in 1859 - that is, "all things have the same origin", that is, all organisms that have ever lived on Earth have a common ancestor.

In 1999, biologist Patrick Fortelle first combined the initials of the words "Last Common Ancestor" and named this hypothetical ancestral organism "LUCA". As the root of the tree of life, Luca later differentiated into life systems including bacteria, archaea and eukaryotes. Since then, countless scientists have embarked on the road to find the "real body" of Luca.

On July 12, 2024, a new study published in the journal Nature Ecology & Evolution took scientists one step further on this path. They found that Luca appeared earlier than previously estimated and had a more complex structure.

The team compared the genomes of 350 archaea and 350 bacteria to find commonalities and to determine which features arose first. They tracked the evolutionary patterns of individual genes and gene families in these archaea and bacteria, respectively, and by comparing the evolutionary history of individual genes with that of species genes, they were able to better explore which genes were duplicated, lost, or experienced horizontal gene transfer.

Based on the above methods, the research team made several important inferences about the origin of life.

First, the common ancestor of life, Luca, appeared about 4.2 billion years ago, which is much earlier than the previously thought 3.8 billion years ago. We know that the Earth was formed about 4.6 billion years ago, which means that the earliest life forms appeared soon after the Earth was formed. This shows that the environment where life originated may be simpler than previously thought.

Secondly, Luca has a very large genome. How large is it? Studies have shown that Luca's genome contains at least 2.5 million base pairs and encodes 2,600 proteins. This is much more complex than previously estimated and is almost as complex as existing prokaryotes.

So how did Luca survive on the early Earth? Scientists have discovered that Luca feeds on hydrogen and carbon dioxide. In an era before the evolution of photosynthetic organs, hydrogen is equivalent to "chemical sunlight", providing an endless supply of energy for Luca's own metabolism, and its metabolic products (such as methane) can become nutrients for other life. So scientists believe that this chemical hydrogen cycle system can support a simple ecosystem, and Luca was not the only life form at the time, but other life forms had become extinct and were unable to leave offspring.

The study also showed that Luca has a gene in his body that resists viral invasion, indicating that life may have the ability or potential to fight viruses shortly after its birth.

Scientists have also found genes in Luca's body that can protect it from ultraviolet damage, which indicates that Luca may not live in deep-sea hydrothermal vents, but may live in surface waters, where they can capture carbon dioxide and hydrogen from the atmosphere to support themselves. On the other hand, they also have an enzyme commonly found in thermophilic bacteria, reverse gyrase, which means that Luca may also thrive around submarine volcanic vents.

Such seemingly contradictory research results are not uncommon in the exploration of the origin of early life. Some scientists also believe that due to the effect of gravity, a large number of asteroids and meteorites bombarded the surface of the earth 3.8 billion years ago, so this period is called the "heavy bombardment period". Under the violent and frequent impacts, liquid water could not exist on the surface of the earth, so early life could not appear.

Since we cannot travel back in time to the time when life was created and witness the scene with our own eyes, it is not difficult to understand such contradictory research conclusions. Moreover, life with only a tiny structure like Luca cannot form fossils in the long geological activities and leave conclusive evidence. We can only use the existing biological and technical means to make speculations as close to the truth as possible. The results of this study are just the beginning. Although it brings together data and methods from multiple disciplines, it seems that we have only got a small piece of the huge puzzle of the origin of life. We still have a long way to go in exploring the ultimate question of mankind: "Where does life come from?"

This article is a work supported by the Science Popularization China Creation Cultivation Program. Author: Liu Sen

Reviewer: Liang Qianjin, Professor of School of Life Sciences, Beijing Normal University

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.