Future mothers aren't the only ones who need to mind the time: A recent study suggests would-be papas have a biological clock too, and it starts ticking at age 35.

Researchers at the University of Washington have found that men in their mid-30s experience a precipitous drop in fertility, according to urologist Dr. Narendra Singh.

"Above 35, there's an increase in the DNA damage in sperm cells," Singh said in a telephone interview. "They get worse and worse over time and are being malformed, and once they become bad, we cannot get rid of them."

The study goes against conventional wisdom -- as well as many high-profile examples -- that men can have children later in life than women. Tony Randall, for example, famously fathered a child when he was 77.

And despite the new study, other reproductive specialists aren't ready to back Singh's findings.

"Does the fact that a man's producing more abnormal sperm in his 40s than in his 20s affect his chances of having an abnormal baby?" Dr. Stewart McCallum, a professor of urology at Stanford University Medical Center, asked. "We can't say that."

The study comes not long after new research into women's reproductive systems sparked a furor when it was found that female fertility declines dramatically after age 35. For weeks, the media focused on female roles at home and in the workplace as women's biological clocks seemed to be ticking louder than ever.

Unlike women, who are born with all their eggs, men generate a tremendous number of sperm cells every day. Naturally, some of them are defective, but men have a quality-control system, whereby bad cells self-destruct -- or at least they're supposed to.

The disturbing part of Singh's study shows that the quality-control system for sperm cells breaks down as men age. That means a larger percentage of sperm never make it to the ovum, and the ones that do are more likely to cause genetic problems that can result in miscarriage or birth defects, according to Singh.

Singh and his colleagues, Dr. Charles Muller and Dr. Richard Berger, conducted their research on 60 volunteers between the ages of 22 and 60, all with healthy sperm counts.

Men shouldn't panic, Singh said, but they should be aware of the new information if they want to have families.

"They should try not to worry about it, but they should do something for it," he said. "Like have a good lifestyle, avoid some kinds of environmental exposure to pesticides and pollutants in the atmosphere, have good nutrition. The second thing they can do is get married early and produce babies early."

However, some experts say Singh's numbers don't necessarily mean men become notably less fertile as they age.

"As we age, we do lose some of that ability to select out the bad cells, but men still have the ability to replenish their supply," McCallum said.

McCallum added that the sheer number of sperm cells keeps the odds in most men's favor.

"I don't think this study would impact most couples substantially," he said. "Will I tell a 40-year-old to stop trying to have children with his 32-year-old partner? No."

Instead of creating baby hysteria among would-be fathers, the study seemed not to faze most men.

Tater Read, a 28-year-old Queens, N.Y., high-school teacher, said his only real concern about his own fertility was the opposite of fear, in fact.

"My worry is that I may get my girlfriend pregnant, and I am not ready to start a family," he said.

In Montreux, Switzerland, Thierry Choinard, a product manager for a Web company, said he wasn't concerned that he hadn't had any children at age 36.

"I don't think about it that often. I think that when the time comes I will have the choice," he said. "I don't smoke, I lead a pretty healthy life. I don't see any reason why I would be infertile just because I'm 36.

"My guys can swim," he added confidently.

If anything, Read said, Singh's study didn't highlight how biologically unsuitable many men are for fatherhood, but how unready they are in other ways.

"Most of us aren't ready to have children financially and emotionally until we're well into our 30s," he said.