The children of older fathers scored lower than the offspring of younger fathers on I.Q. tests and a range of other cognitive measures at 8 months old, 4 years old and 7 years old, according to a study released Monday that added to a growing body of evidence suggesting risks to postponing fatherhood.

The study is the first to show that the children of older fathers do not perform as well on cognitive tests at young ages. Although the differences in scores were slight and usually off by just a few points on average, the study’s authors called the findings “unexpectedly startling."

“The older the dads were, the slightly worse the children were doing,” said Dr. John J. McGrath, the paper’s senior author and a professor of psychiatry at the Queensland Brain Institute in Brisbane, Australia. “The findings fit in a straight line, suggesting there may be some steady beat of mutations happening in the dad’s sperm.”

Earlier studies have found a higher incidence of schizophrenia and autism among the offspring of men who were in their mid-to-late 40s or older when they had children. A study published in 2005 reported that 16-year-olds and 17-year-olds with older fathers scored lower on nonverbal I.Q. tests, as did the offspring of teenage fathers.