SCIENTIFIC AMERICAN ARTICLE NAILS THE GENETIC MALE BIOLOGICAL CLOCK

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"Fisch and his colleagues have also found that the children of women over 35 whose babies' fathers were also of that age were more likely to have Down's syndrome than offspring whose fathers were younger."

"In other studies, older men were more likely to father children with mental illness or other deficits. Roughly 11 children out of a thousand conceived by men over age 50 developed schizophrenia compared with under three children out of a thousand for fathers under 20 in one study from the Archives of General Psychiatry. And the children of men 40 years or older were nearly six times more likely to have autism spectrum disorders than kids begot by men under 30."

"So do men's sperm get staler over time? To maintain sperm levels, cells known as germ cells must continue dividing. After all, men find ways to dispose of sperm—ahem—and once ejaculated they only survive for several days. By the age of 50, these germ cells will have divided 840 times. Each one of those divisions is an opportunity for something to go wrong. "There's more of a chance to have genetic abnormalities the more the cells divide," Fisch says. In sperm these mutations dot the genes with changes in the basic structure of the DNA—and can lead to problems in the resulting offspring."