12 hours ago
Men are losing the Y chromosome: What it means for men's health and aging
For years, we've been taught that men have one X and one Y chromosome, with the Y carrying the vital gene that initiates male development. But now, scientists are sounding the alarm: the Y chromosome is slowly disappearing.
Unlike the X, which holds hundreds of genes, the Y has lost most of its genetic content over millions of years. Some researchers predict it could vanish entirely in about 11 million years. While that may seem far away, evidence suggests the effects of Y chromosome loss are already showing up in men today — especially in how they age and stay healthy. The complete study is published in the journal
Cell
.
How Y chromosome is fading in men
Compared to its counterpart, the X chromosome, which carries around 900 genes, the Y is tiny and holds just about 55 genes.
Genetic studies show that over millions of years, the Y chromosome has been steadily losing genes. Researchers estimate that if this trend continues, the Y could disappear completely in roughly 11 million years. That might sound far off, but clues from both animals and humans suggest the effects may already be happening — and they're not just theoretical.
Men already losing Y chromosomes in their cells
Long before the chromosome disappears from the species, many men are already starting to lose it in some of their cells.
Starting around age 50, some bone marrow cells begin to misplace the Y chromosome during cell division. These Y-less cells multiply, especially in the blood. By the time a man reaches 80, about 4 in 10 have a significant amount of blood cells missing the Y — a condition known as "mosaic loss of Y," or LOY.
A long-term study in Sweden tracked over 1,100 older men and found that those with LOY had higher risks of cancer, heart disease, and Alzheimer's, and died an average of 5.5 years earlier than those without the condition.
Why losing the Y matters to the immune system
One of the genes on the Y chromosome, called UTY, helps regulate the immune system. When it's gone, certain immune cells stop working the way they should. Some start producing more scar tissue, while others become weaker and less able to fight cancer.
In lab tests, mice without the Y chromosome developed faster-growing tumors and more heart damage. In humans, tumors that lack the Y — especially in the bladder — tend to be more dangerous.
But there's a twist: these same tumors also respond better to a specific cancer treatment called checkpoint inhibitors. It's a reminder that biology often works in unexpected ways.
Results of the research done on rodents
Some rodent species, like the Japanese spiny rat and certain mole voles, have already lost their Y chromosomes completely — and yet, they still manage to produce male offspring. In 2022, scientists discovered that a copy of DNA near a gene called SOX9 can take over the job of turning on male development, even without the usual Y-linked trigger.
This finding suggests that evolution can find workarounds. If the Y disappears in humans one day, it's possible that a new system could emerge to take its place.
What can men do to prevent the Y chromosome loss
While we can't stop evolution, we can slow down the loss of the Y chromosome in our own bodies. Things like smoking, air pollution, and exposure to toxic chemicals speed up DNA damage, including Y chromosome loss. Quitting smoking, avoiding environmental toxins, and leading a healthy lifestyle — with regular exercise, nutritious food, and good sleep — may help preserve more Y-bearing cells.
Some drugs used to treat lung disease are being tested to see if they can prevent the heart damage linked to Y loss. And as medical tests become more advanced and affordable, men might soon be able to get a 'Y-loss score' during regular checkups, much like cholesterol levels.
A story of evolution and urgency
The shrinking Y chromosome sits at a strange crossroads between slow evolutionary change and urgent medical challenges. On one hand, nature seems to have a backup plan for the far future.
On the other hand, individual men today are already feeling the consequences in their health.
It's a perfect example of how evolution and medicine don't always share the same timeline. Evolution cares about passing on genes, not about living into your 80s. But for doctors and patients, the immediate risks matter more.
Even though the idea of the Y chromosome disappearing sounds alarming, there's no need for panic. Evolution is adaptable, and medical science is catching up fast. For now, the most practical advice is simple: stay healthy, avoid harmful chemicals, and pay attention to new research.
The complete study is published in the journal
Cell
.
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