Men should freeze some of their sperm at 18 to reduce the risk of having a disabled child, an expert said yesterday.
The chance of fathering a child with disorders such as autism and schizophrenia increases the older a man gets, possibly because sperm deteriorates with age.
Dr Kevin Smith, a bioethicist at Abertay University in Dundee, warned that if nothing was done there would be a gradual reduction of "human fitness in the long term". However, fertility doctors said the idea was "crackers" and accused him of promoting an unnecessarily artificial approach to parenthood.
They also claimed the risks were small and did not kick in until men were past 45.
Writing in the Journal of Medical Ethics, Dr Smith said: "Earlier fatherhood is desirable in terms of maximising genetic integrity.