Bioengineer Narendra Singh of the University of Washington in Seattle and his colleagues compared the sperm of men of different ages. Sure enough, sperm in men older than 35 had more DNA damage than that from younger men. And although unhealthy sperm are supposed to commit cell suicide, some of the sperm they looked at had lost that ability to "take one for the team"—meaning they'd be around to fertilize an egg. "This may lead to offspring with defective DNA, which may translate to mental and physical defects," Singh says.
Can men prevent this damage? No, but they may be able to mitigate it. There are factors within men's control that can accelerate adverse effects: alcohol, smoking, drugs and environmental pollution—even coffee consumption. So avoid them, says Singh.
Still, even after correcting for various lifestyle factors, the DNA of sperm are increasingly damaged with advancing age.
"The question is, can we reverse the [male] biological clock?" asks Fisch, who is studying various ways to keep sperm healthy.
Perhaps Bridget Jones's Uncle Geoffrey and Aunt Una should have chastised her love interest, Mark Darcy, too, for procrastinating procreation. That "tick-tock, tick-tock," it would seem, applies to both sexes.