For decades, scientists have largely agreed on one prevailing theory about the origins of life on Earth: the RNA world hypothesis.
This idea suggests that RNA—the simpler molecular cousin of DNA—was the first self-replicating molecule and laid the groundwork for the emergence of complex life.
But new research from the Scripps Research Institute in California is turning that assumption on its head.
According to the study, RNA alone may not have been able to sustain the evolution of life.
Instead, scientists now propose that RNA and DNA might have formed at the same time, working together from the very beginning.
If this turns out to be true, it would fundamentally alter our understanding of how life originated—not just on Earth, but potentially across the universe.
The Classic RNA World Hypothesis—And Its Flaws
The RNA world hypothesis has dominated the conversation about the origins of life for years.
According to this theory, around 3.8 billion years ago, RNA molecules self-assembled in Earth’s primordial soup.
These molecules were believed to be the first self-replicators, capable of encoding genetic information and catalyzing chemical reactions.
Over time, RNA is thought to have given rise to DNA, which eventually became the blueprint for all life as we know it.
The theory is compelling, but it has one major flaw: RNA is chemically unstable.
Unlike DNA, which forms a stable double helix, RNA is more fragile and susceptible to breaking down.
It’s difficult to imagine how RNA alone could have sustained life long enough to transition into the more resilient DNA-based system we see today.
That’s where the new research comes in.
Scientists at Scripps tested whether RNA and DNA could have coexisted in early life forms—and what they found might rewrite biology textbooks.
Partners from the Beginning?
Led by chemist Ramanarayanan Krishnamurthy, the team at Scripps set out to test a critical assumption of the RNA world hypothesis: Could RNA have naturally evolved into DNA by forming chimera strands—hybrids of the two molecules?
To find out, the researchers created synthetic RNA-DNA hybrids in the lab and tested their stability. The results were surprising:
- RNA-DNA chimeras were highly unstable, making it unlikely that they could have sustained life.
- The blended strands experienced a drastic drop in thermal stability, meaning they would have fallen apart quickly in Earth’s early environment.
- Instead of naturally transitioning into DNA, RNA would have been more likely to self-destruct or revert to pure RNA molecules.
“We were surprised to see a very deep drop in what we would call the ‘thermal stability’,” Krishnamurthy explained. This means that early RNA-DNA hybrids would have struggled to replicate, casting doubt on the idea that RNA alone could have given rise to DNA.
What If DNA Was Always There?
For years, the dominant narrative has been that RNA came first, and DNA evolved later.
But what if we’ve been thinking about it all wrong?
Krishnamurthy and his colleagues now propose an alternate hypothesis: RNA and DNA co-evolved together, rather than one emerging from the other.
In this scenario, both molecules formed simultaneously from similar ingredients in Earth’s early environment.
This idea makes a lot of sense when you consider another key point: Even in today’s cells, RNA and DNA don’t mix well.
If RNA nucleotides mistakenly join a DNA strand, cellular enzymes rush in to correct the mistake.
If RNA and DNA struggled to interact even billions of years ago, how could RNA have smoothly transitioned into DNA in the first place?
The Need for a New Model
The implications of this research are profound.
If RNA and DNA coexisted from the beginning, it would mean:
- Life may have had a more complex start than we assumed—not a single RNA-based world, but a mixed system from the very beginning.
- The origins of life may be more common than we think. If both RNA and DNA can form under natural conditions, this increases the likelihood of finding life on other planets.
- Scientists need to rethink prebiotic chemistry—the study of how life’s building blocks formed. Many experiments have focused solely on RNA, but this research suggests we should be looking at RNA and DNA together.
According to David Deamer, a biochemist from the University of California, Santa Cruz, who was not involved in the study, this shift in perspective could be “a game-changer for understanding how life began.”
What Comes Next?
Of course, this isn’t the end of the debate.
Scientists still need to determine exactly how RNA and DNA could have formed together—and whether they could have worked together to kickstart life.
Future research will likely focus on:
- Finding natural chemical pathways that allow both RNA and DNA to form under prebiotic conditions.
- Examining other possible self-replicating molecules that might have played a role.
- Testing this hypothesis in more complex simulations of early Earth’s environment.
Krishnamurthy himself acknowledges that more work is needed, but he remains optimistic.
“Even if you believe in an RNA-only world, you have to believe in something that existed with RNA to help it move forward,” he says.
“Why not think of RNA and DNA rising together?”
A New Era of Understanding Life’s Origins
This study presents a bold challenge to one of the most widely accepted ideas in biology.
While the RNA world hypothesis has dominated scientific thought for decades, new evidence suggests it may not tell the whole story.
Instead, RNA and DNA may have co-evolved, working in tandem from the start.
If this theory holds up, it could completely change how we search for life beyond Earth.
If both RNA and DNA can form under natural conditions, life might be far more common in the universe than we ever imagined.
One thing is certain: we are still uncovering the secrets of how life began, and every new discovery brings us closer to the truth.
