Children of older fathers are likely to be less mentally agile than those of young fathers, a study suggest.

John McGrath, a psychiatrist and epidemiologist at the Queensland Brain Institute at the University of Queensland in Australia, carried out a cognitive function tests that includes IQ tests, discrimination and perception tests and concentration tests on 33,437 kids at four months, four years, and seven years. The children of 20-year-old fathers had an average IQ of 106.8 while those of 50-year-old fathers had an average IQ of 100.7.

But children with older mothers had better cognitive functions. Since women are born with ova that they will use their whole life, the quality of the ova is not affected by age. However, since men make sperm throughout their life, they develop more DNA mutations, negatively affecting the development of their children¡¯s brain, McGrath said.