It is well-know women have ticking biological clocks, and that older women run the risk of conceiving children with birth defects. However, it now appears men have a shelf life on their reproductive capacities as well. Although the change is slow in men, as they age their sperm count decreases and their sperm become less active.

Researchers found that since 1980, men between the ages of 35 and 49 have been having 40 percent more children then before, and the number of children from men under 30 has decreased as well.

CBS news reported that the study was funded by the National Institute of Environmental Health Sciences, part of the National Institutes of Health, and the U.S. Environmental Protection Agency.