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Space & Astronomy
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Unraveling the Myth: How Spaceflight Changes Gene Expression, Not an Astronaut's Core DNA
Contrary to viral headlines, Scott Kelly's DNA did not permanently change after a year in space. The myth stems from NASA's Twins Study, which found significant changes in his *gene expression*—how genes turn on and off—most of which reverted upon his return to Earth.
In 2018, a headline went viral: after a year in space, astronaut Scott Kelly’s DNA had been permanently altered, and he was no longer the identical twin of his brother, Mark. It was a tantalizing story that captured the public imagination, suggesting that space travel could fundamentally rewrite our genetic code. The truth, however, is far more nuanced and scientifically fascinating. While Scott Kelly underwent a battery of incredible biological changes, his core DNA blueprint remains unchanged.
The Perfect Experiment: The NASA Twins Study
The source of this myth was one of the most ambitious human studies ever conducted: The NASA Twins Study. For 340 days, Scott Kelly orbited Earth aboard the International Space Station while his identical twin brother, former astronaut Mark Kelly, remained on the ground. This provided a perfect, single-variable experiment. With identical genomes, scientists could directly compare the brothers to isolate the specific effects of long-duration spaceflight on the human body.
Gene Expression: The Software to DNA's Hardware
The confusion arose from a misunderstanding between fundamental DNA and gene expression. Think of your DNA as the hardware of a computer—the permanent, underlying code that makes you who you are. Gene expression, on the other hand, is the software. It’s the process of genes being turned “on” or “off” in response to environmental factors like diet, stress, and, in Scott's case, microgravity and space radiation. Your hardware doesn't change, but the programs you run on it can. The study found that thousands of Scott's genes changed their expression levels while he was in space. This is not a mutation; it's adaptation. His body was simply running different genetic “software” to cope with the extreme environment.
What Really Changed in Space?
The study revealed a host of physiological shifts, many of which reverted to normal shortly after Scott's return to Earth. While the vast majority—over 90%—of his gene expression changes returned to their pre-flight baseline, a small fraction did not. These persistent changes offer critical clues for safeguarding future astronauts on long journeys to Mars and beyond.
Key Findings of the Twins Study
- Telomere Dynamics: In a surprising twist, the protective caps at the ends of Scott’s chromosomes, called telomeres, actually lengthened in space. On Earth, telomeres typically shorten as we age. However, upon his return, they rapidly shortened back to and even beyond his pre-flight levels.
- DNA Damage: As expected, Scott experienced a higher level of chromosome aberrations due to increased radiation exposure. This underscores a known risk of spaceflight, but it is not the same as his entire genetic code being rewritten. His body's DNA repair mechanisms were still active.
- The Immune System: Researchers observed that Scott's immune system responded appropriately in space, even reacting as expected to a flu vaccine administered in orbit.
- Cognitive Effects: Upon returning, Scott experienced a slight decrease in cognitive speed and accuracy, which largely returned to normal over the next six months.
Ultimately, Scott Kelly is still very much an identical twin to Mark. The Twins Study didn't reveal a man mutated by the cosmos but rather a testament to the human body's remarkable plasticity. The viral myth, while incorrect, inadvertently highlighted a profound truth: space travel challenges the human body down to the genetic level, not by changing our fundamental code, but by forcing it to adapt in ways we are only just beginning to understand.