For decades, most of the focus on genetic risks in childbirth has centered around maternal age. But groundbreaking new research now shows that a father’s age may be just as important — and possibly even more impactful — when it comes to passing on harmful genetic mutations to children.
A large-scale study published in New Scientist reveals that older men are far more likely to pass on disease-causing mutations through their sperm, increasing the risk of autism, developmental disorders, and even cancer in their offspring. The reason lies in a process scientists are calling “selfish sperm.”
What Is “Selfish Sperm”?
As men age, the stem cells responsible for producing sperm continue dividing throughout life. Over time, some of these cells pick up random genetic changes, or mutations. Most of these mutations are harmless — but a few can actually give certain sperm-producing cells a growth advantage.
These mutated cells start multiplying faster than normal ones, eventually dominating sperm production. This means that as men grow older, a larger percentage of their sperm carries potentially harmful mutations — the so-called “selfish” ones that prioritize their own replication over the health of future generations.
Shocking New Numbers
The study’s findings are striking. Among men in their early 30s, roughly 1 in 50 sperm carried a harmful genetic mutation. By age 70, that figure had climbed to nearly 1 in 20.
This isn’t simply a gradual, age-related increase — it’s an exponential rise, suggesting that these selfish mutations spread aggressively over time. Researchers say this steep jump in mutation load could help explain why the risks of certain conditions, like autism spectrum disorders and rare childhood cancers, increase with a father’s age.
Which Genes Are Affected?
Using advanced genome sequencing, scientists identified more than 40 genes that can be influenced by these selfish mutations. Many of these genes are critical for brain development and cell growth control — the same biological systems involved in autism and cancer.
One example is the FGFR2 gene, which is linked to craniosynostosis, a serious skull-development disorder, as well as certain cancers. Another is the PTPN11 gene, associated with Noonan syndrome and leukemia. Mutations like these can arise naturally, but the study shows they become much more common as men age.
Lifestyle Factors Play a Smaller Role
Interestingly, while unhealthy habits such as smoking and drinking are known to increase mutation rates in other parts of the body — particularly in blood cells — the research found that sperm cells are largely protected from environmental damage.
That means the key driver behind the rise in sperm mutations isn’t lifestyle or diet, but age itself. Each year, sperm stem cells divide again and again, and with every division comes a small chance of mutation. Over decades, those chances add up.
Why This Matters
This discovery could reshape how we think about reproductive health and family planning. For a long time, society has placed emphasis on a woman’s biological clock — but science now shows that men have one too, even if it ticks more quietly.
While the absolute risk of a child developing a serious disorder due to paternal mutations remains relatively low, the cumulative effect at the population level could be significant. As more people choose to have children later in life, understanding and communicating these risks becomes increasingly important.
Doctors and genetic counselors may soon start discussing paternal age more openly when advising couples trying to conceive. It could also inspire new fertility tests or genetic screenings designed specifically to detect harmful sperm mutations before conception.
A New View of Fatherhood and Genetics
The study’s authors stress that age-related risks don’t mean older fathers shouldn’t have children. Rather, this research provides vital insight into how male fertility and genetics evolve over time — knowledge that can help families make more informed decisions.
It also highlights a fascinating paradox: the same biological mechanisms that keep sperm production going for decades may, in the end, become the very source of genetic danger.
In the words of one researcher, “Nature designed sperm to keep producing, but not necessarily to keep producing perfectly.”
Source:
Le Page, M. (2025, October 8). Selfish sperm see older fathers pass on more disease-causing mutations. New Scientist.