Older men are more likely than young ones to father a child who develops autism or schizophrenia, because of random mutations that become more numerous with advancing paternal age

Research provides support for the argument that the surging autism diagnoses rate over recent decades is attributable in part to increasing average age of fathers, which could account for as many as 20% to 30%. The risk of chromosomal abnormalities, such as Down syndrome, increases for older mothers. Researchers have found that the average child born to a 20-year-old father had 25 random mutations that could be traced to paternal genetic material. The number increased steadily by two mutations a year, reaching 65 mutations for offspring of 40-year-old men.