A British bioethicist has called for all 18-year-olds to freeze their sperm in case they plan on having children later in life.
The sperm of older men contain a greater number of mutations that can put their children at an increased risk of suffering genetic disorders, said Dr Kevin Smith, of Abertay University in Dundee.
He believes that earlier fatherhood should be promoted to young men and that the NHS should support sperm banking to avoid the risk of "gradually reducing human fitness in the long term".
Writing in the Journal of Medical Ethics, he said: "If demographic trends towards later fatherhood continue, this will likely lead to more children suffering from genetic disorders."
However, Dr Allan Pacey, a professor of andrology at the University of Sheffield, told the BBC the suggestion was "one of the most ridiculous suggestions I have heard in a long time."
He said that the majority of sperm doesn't freeze very well and described the risks from later fatherhood as "really quite small".