New Research Uncovers All Humans Share a Common Ancestor— And it’s Not Adam

By: Alyssa Miller | Last updated: Sep 11, 2024

Diversity is often hailed as the essence of beauty—an observation that is readily apparent when we consider the vibrant array of flowers, animals, landscapes, and humans that populate our world.

Yet, this remarkable diversity wasn’t always the norm. In fact, all life on Earth traces its lineage back to a singular origin.

The True Ancestor Humans: LUCA

Contrary to popular beliefs—like those found in biblical texts—the progenitor of all living organisms wasn’t named God or Adam but is known as LUCA.

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LUCA diagram

Source: New Scientist

LUCA stands for “Last Universal Common Ancestor,” a term used by scientists to describe a fundamental, primitive organism from which all life has descended.

How We Are Related to LUCA

Modern life evolved from LUCA from various sources. These sources include amino acids used to build proteins in all cellular organisms, the shared energy currency, the presence of cellular machinery, and DNA’s purpose of storing information.

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A photograph of a family hiking in the forest

Source: Wikimedia

This is what makes all organisms that function under these sources related.

The Ancient Root of All Life

This tiny, rudimentary life form is considered the root of the entire tree of life, encompassing everything from the tiniest bacteria to the most massive creatures that have ever existed.

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An up-close photograph of a purple bacterium

Source: Wikimedia

Recent research, however, has revealed that LUCA’s existence may date back even further than previously thought

New Findings Suggest LUCA Predates Earlier Estimates

For a long time, scientists estimated that LUCA emerged approximately 4 billion years ago—around 600 million years after the Earth was formed.

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A photograph of Earth

Source: Wikimedia

But new findings, detailed in a recent study published in Nature Ecology & Evolution, suggest that LUCA might have appeared even earlier.

Discovering LUCA’s Age in Ancient Bones

According to Live Science, “[T]he researchers counted the mutations that have occurred over time across the genomes and within 57 genes shared by all 700 organisms, using estimated mutation rates to back-calculate when LUCA lived.”

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Human leg bones in a crossed pattern.

Wellcome Images/Wikimedia Commons

The team then moved on to the next stage of determining a more accurate estimate of LUCA’s age.

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Dating LUCA

Scientist Edmund Moody and his colleagues from the University of Bristol compared all the genes in the genomes of living species in a new study, counting the mutations that have occurred in their sequences over time.

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Close-up photograph of a high-tech microscope in a lab

Source: Christopher Furlong/Getty Images

Since these organisms all come from LUCA, the time of separation can reveal how old LUCA is.

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Finding LUCA’s Age

While LUCA was previously believed to be 3.9 billion years old, researchers were able to refine this estimate using fossils that contained traces of ancient life. One of these fossils contained 3.48-billion-year-old microbial mats.

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Screenshot of a YouTube video showing the encysting of a microscopic Euglenid

Source: ProtistLabFilms/YouTube

These ancient fossils provided the team with insights into early Earth’s atmospheric conditions and helped them estimate LUCA’s age.

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The Evolution of LUCA

“The evolutionary history of genes is complicated by their exchange between lineages,” Dr. Moody said. “We have to use complex evolutionary models to reconcile the evolutionary history of genes with the genealogy of species.”

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A photograph of two researchers working in their lab

Source: Wikimedia

“We did not expect LUCA to be so old, within just hundreds of millions of years of Earth formation,” said Dr. Sandra Álvarez-Carretero, also from the University of Bristol. “However, our results fit with modern views on the habitability of early Earth.”

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Comparing LUCA to Ancient Bacteria

Researchers have compared LUCA’s origins by analyzing the genes of 700 living species of bacteria and archaea—microbes similar to bacteria that often live in extreme environments.

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A scientist is pictured examining a test sample using a microscope

Source: Freepik

Scientists believe these organisms are the oldest life forms, with eukaryotes evolving from a union of the two cell types.

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Looking Closer

By remodeling the physiological characteristics of modern living species, the study’s authors were able to work out the biology of LUCA.

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Scientist examining a sample under a microscope

Source: Freepik

“One of the real advantages here is applying the gene-tree species-tree reconciliation approach to such a diverse dataset representing the primary domains of life Archaea and Bacteria,” said University of Bristol’s Dr. Tom Williams.

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Genetic Analysis

To achieve this, they employed a technique that involved analyzing genetic data from modern species and tracking the mutations that have accumulated since these species diverged from their common ancestor—LUCA.

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A close-up photo of a genetic sequence

Source: Sangharsh Lohakare/Unsplash

By applying a genetic equation to estimate the separation time between species, the team concluded that LUCA may have been around as early as 400 million years after Earth’s formation.

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Not Too Different From Modern Organisms 

“Our study showed that LUCA was a complex organism, not too different from modern prokaryotes,” said University of Bristol’s Professor Davide Pisani. Prokaryotes are microscopic single-celled organisms that do not have a distinct nucleus with a membrane or specialized organelles.

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Two researchers pictured working from their desk

Source: Freepik

Dr. Pisani continued: “… but what is really interesting is that it’s clear it possessed an early immune system, showing that even by 4.2 billion years ago, our ancestor was engaging in an arms race with viruses.”

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Life Amidst Earth’s Fiery Beginnings

This new timeframe places LUCA squarely within the Hadean Eon, a tumultuous period named after Hades, the Greek god of the underworld.

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The edge of the Darvaza crater.

Source: Hellbus/Wikimedia

The Hadean Eon, which also draws from the Hebrew word for “hell,” was characterized by extreme conditions, including a molten surface, relentless volcanic eruptions, and frequent asteroid impacts.

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LUCA Thrived in the Ocean

The team also determined where LUCA thrived before evolving into modern life. Although the analysis did not pinpoint LUCA’s exact habitat, it suggested that LUCA lived in a shallow, warm ocean environment.

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Waves Crash Along Coast In San Diego

Source: Kevin Carter/Getty Images

The findings also indicated that LUCA likely tolerated extreme temperatures and “breathed” without oxygen.

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Surviving the Extreme

The fact that LUCA managed to survive in such a harsh environment is remarkable.

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The Door to Hell creator seen at night.

Source: flydime/Wikimedia

The researchers were keen to understand how this early ancestor endured these brutal conditions.

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LUCA's Primitive Immunity

Their investigation revealed that, despite LUCA’s simplicity as a prokaryote—a single-celled organism lacking a nucleus and membrane-bound organelles—it likely possessed a primitive immune system.

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Close-up photograph of single-celled organisms under a microscope

Source: iStock

This early immune system would have enabled LUCA to fend off the primordial viruses that were pervasive at the time.

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Early Microbial Ecosystems and Recycling

Tim Lenton, a co-author of the study from the University of Exeter, noted, “It’s clear that LUCA was exploiting and changing its environment, but it is unlikely to have lived alone.”

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A photograph of microbes

Source: Wikimedia

“Its waste would have been food for other microbes, like methanogens, that would have helped to create a recycling ecosystem.”

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Creating a Recycling Ecosystem

“It’s clear that LUCA was exploiting and changing its environment, but it is unlikely to have lived alone,” said Dr. Tim Lenton, a researcher at the University of Exeter.

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A close up of microbes on the ocean floor

Source: Australian Institute of Marine Science

The researchers believe that LUCA’s waste would have been food for other microbes that existed around the time, like methanogens, encouraging a recycling ecosystem that depended on each organism.

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Ongoing Research

Although LUCA remains the oldest known common ancestor, the path from this primordial life form to the complex organisms we see today is still a subject of ongoing research.

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A photograph of a scientist in a lab

Source: Wikimedia

Scientists continue to delve into our primordial past to uncover the intricate processes that led to the evolution of complex life and the remarkable diversity that defines our world today.

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Unraveling the Evolution from LUCA to Modern Diversity

Further exploration is needed to fully understand how life evolved from its earliest beginnings.

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A massive amount of people seen in New York City in the evening.

Source: Jakub Hałun/Wikimedia Commons

Additionally, this research will help clarify how these early forms of life gave rise to the extraordinary variety of organisms we see today.

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Detailed Insights into LUCA and Early Earth

The research not only pushes back the timeline of LUCA’s existence but also provides fascinating insights into its characteristics and the conditions of early Earth.

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A photograph of the Earth from space

Source: Alexander Gerst/ESA via Getty Images

An international team of researchers from the UK, Netherlands, Hungary, and Japan undertook the challenge of pinpointing LUCA’s exact appearance on Earth.

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Life on Early Earth

“The findings and methods employed in this work will also inform future studies that look in more detail into the subsequent evolution of prokaryotes in light of Earth history, including the lesser studied Archaea with their methanogenic representatives,” said Professor Anja Spang, a researcher at the Royal Netherlands Institute for Sea Research.

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A photograph of the Earth from space

Source: Wikimedia

The research demonstrates how the ecosystem of the time was able to establish an early version of Earth.

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The Theory of Evolution and Natural Selection

Darwin developed a theory, often described as the theory of evolution by natural selection, which recognizes that all living organisms on Earth today trace back to one or a few “original progenitors.”

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A photograph of a researcher writing at his desk

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Although common ancestry and natural selection are logically independent, they are interconnected. Natural selection has eliminated cells, proteins, and everything else that could not sustain life or produce offspring.

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Theories That Play Into Each Other

In On the Origin of Species, Darwin noted: “…adaptive characters, although of the utmost importance to the welfare of the being, are almost valueless to the systematist.”

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Opened book on a wooden table

Source: Freepik

He continued: “One might expect natural selection to cause the torpedo shape to evolve in large aquatic predators, whether or not they have a common ancestor. This is why adaptive similarity is almost valueless to the systematist who is trying to reconstruct patterns of common ancestry.”

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Finding a Common Link

Understanding natural selection is essential for discovering and interpreting evidence about common ancestry. The process of natural selection is driven by environmental conditions and can occur even if two species do not share a common ancestor.

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A photograph of to researchers looking at test results on screens

Source: Freepik

However, every living organism must have originated from something. Contrary to certain beliefs, modern humans did not come into existence as they are today.

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Life Like LUCA Could Be Elsewhere

“Our work draws together data and methods from multiple disciplines, revealing insights into early Earth and life that could not be achieved by any one discipline alone,” said University of Bristol’s Professor Philip Donoghue.

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A researcher is pictured smiling at her desk

Source: Wikimedia

“This suggests that life may be flourishing on Earth-like biospheres elsewhere in the Universe.”

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10 Planets That Could Host Life

Currently, ten planets could closely resemble Earth, supporting life like LUCA and eventually a future species like humans.

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A group of people sitting outdoors together and looking at a view.

Source: Roberto Nickson/Unsplash

According to Space, a potentially life-friendly planet must be relatively small and orbit in the habitable or “Goldilocks” zone of its star. This would allow water to exist in liquid form on the world’s surface.

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Gliese 667Cc

One planet that could potentially support life like LUCA is 22 light-years from Earth and is at least 4.5 times as massive as Earth, according to NASA’s Jet Propulsion Laboratory.

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More details This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system.

Source: Wikimedia Commons

Known as Gliese 667Cc, the planet completes one orbit around its host start in 28 days, but the star is a red dwarf, and is considerably cooler than the sun. However, the planet’s proximity to the sun could cause life to be baked by flares from the red dwarf.

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Kepler-22b

Kepler-22b is located 600 light-years away and is considerably larger than Earth. Dubbed the “super-Earth,” it is unclear if the planet is rocky, liquid, or gaseous.

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An artist rendition of Kepler-22b

Source: NASA

Kepler-22b’s orbits a G-class star, which is smaller and colder than Earth’s, in 290 days, which is pretty similar to Earth’s 365.

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Kepler-69c

Located about 2,700 light-years away, Kepler-69c, which is 70 percent larger than Earth, is located in a habitable zone, but researchers are unsure about its composition.

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The artist's concept depicts Kepler-69c, a super-Earth-size planet in the habitable zone of a star like our sun, located about 2,700 light-years from Earth in the constellation Cygnus.Kepler-69c, is 70 percent larger than the size of Earth, and is the smallest yet found to orbit in the habitable zone of a sun-like star.

Source: NASA

However, Kepler-69c’s host star is about 80 percent as luminous as the sun, which makes the planet habitable by some sort of life.

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Kepler-62F

This planet is about 40% larger than Earth and orbits a star that is much cooler than our sun. NASA notes that the planet orbits its star in 267 days. Despite these differences, the planet is in the habitable zone.

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Astronaut photograph of the two blobs of light on October 30, 2021. The two lights are the moon (top right) and a lightning storm (bottom middle) seen from the ISS.

Source: Johnson Space Center

Kepler-62F lies about 1,200 light-years away. Due to its large size, it is possible that the planet is potentially rocky and may hold oceans.

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Kepler-186F

Appearing to be about 10% larger than Earth, Kepler0186F rotates around its star just on the edge of the habitable zone. The planet receives just a third of its energy from its star, which is significantly less than what Earth gets from the sun.

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X-Shaped Structure Detected at Center of Our Milky Way Galaxy

Source: @dailygalaxy/X

The planet’s star is a red dwarf, which makes the planet far less than Earth’s true twin.

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Kepler-442B

Despite being only 33% larger than Earth, this planet orbits its star every 112 days. Time does fly by on this planet, yet it orbits in the habitable zone.

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A photograph of several stars in space

Source: Wikimedia

One study from the Monthly Notices of the Royal Astronomical Society in 2021 found that the planet receives enough light to sustain a large biosphere, increasing the likelihood of the planet’s ability to create photosynthesis.

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Kelper-452B

Discovered in 2015, the near-Earth-size planet orbits around a star the size of the sun, according to NASA.

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A photograph of several large and bright stars in space

Source: Wikimedia

At 1.6 times the size of Earth, Kepler-452b has a “better than even chance” of being rocky, its discoverers have said.

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Kepler-1649C

Scientists discovered Kepler-1649C after reanalyzing data from NASA’s Kepler Space Telescope. The planet looked to be in similar size to Earth and orbited its star in the habitable zone.

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A photograph of Earth from space

Source: Wikimedia

During the initial data collection from the telescope, a computer algorithm misidentified the astronomical body, according to NASA, but in 2020 it was discovered to be a planet.

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