Women's biological time clock has long been known, with older women having an increased risk of miscarriage and of producing children with genetic defects such as Down Syndrome, according to Forbes.
Researchers say, men also have biological time clock. Men seem to have a gradual rather than an abrupt change in fertility and in the potential ability to produce viable, healthy offspring.
Both men and women have been postponing parenthood in recent years. Since 1980, the researchers said, birth rates have increased 40 percent for men aged 35 to 49, while there has been a decline in births involving men under 30.
The same team had previously found that as men age their sperm count declines and their sperm becomes less active.
The study was primarily funded by several grants from the National Institute of Environmental Health Sciences, part of the National Institutes of Health, and the U.S. Environmental Protection Agency, CBS News reports.
The Russian missile cruiser Varyag, which is currently staying in the waters of the Mediterranean Sea, blocked the US Navy aircraft carrier strike group in the Adriatic Sea